PEP-8 long lines and dunders (#245)

This patch massively reformats the whole codebase mainly wrapping
long lines and eliminating dundered private attributes.

88 files changed, 3846 insertions, 2308 deletions

diff --git a/examples/hlapi/v1arch/asyncio/agent/ntforg/default-v1-trap.py b/examples/hlapi/v1arch/asyncio/agent/ntforg/default-v1-trap.py
index d63332f9..dfaefc62 100644
--- a/examples/hlapi/v1arch/asyncio/agent/ntforg/default-v1-trap.py
+++ b/examples/hlapi/v1arch/asyncio/agent/ntforg/default-v1-trap.py
@@ -21,6 +21,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/examples/hlapi/v1arch/asyncio/agent/ntforg/multiple-notifications-at-once.py b/examples/hlapi/v1arch/asyncio/agent/ntforg/multiple-notifications-at-once.py
index f81c909d..3b6f7513 100644
--- a/examples/hlapi/v1arch/asyncio/agent/ntforg/multiple-notifications-at-once.py
+++ b/examples/hlapi/v1arch/asyncio/agent/ntforg/multiple-notifications-at-once.py
@@ -18,6 +18,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/examples/hlapi/v1arch/asyncio/manager/cmdgen/getbulk-to-eom.py b/examples/hlapi/v1arch/asyncio/manager/cmdgen/getbulk-to-eom.py
index c0532c09..e3043239 100644
--- a/examples/hlapi/v1arch/asyncio/manager/cmdgen/getbulk-to-eom.py
+++ b/examples/hlapi/v1arch/asyncio/manager/cmdgen/getbulk-to-eom.py
@@ -18,6 +18,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-concurrent-queries-over-ipv4-and-ipv6.py b/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-concurrent-queries-over-ipv4-and-ipv6.py
index f0e14ae5..0a496bd6 100644
--- a/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-concurrent-queries-over-ipv4-and-ipv6.py
+++ b/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-concurrent-queries-over-ipv4-and-ipv6.py
@@ -18,6 +18,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-sequential-queries.py b/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-sequential-queries.py
index 3ce3c232..12f7a142 100644
--- a/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-sequential-queries.py
+++ b/examples/hlapi/v1arch/asyncio/manager/cmdgen/multiple-sequential-queries.py
@@ -18,6 +18,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/examples/hlapi/v1arch/asyncio/manager/cmdgen/v1-get.py b/examples/hlapi/v1arch/asyncio/manager/cmdgen/v1-get.py
index 5659a3a5..ba54d1bd 100644
--- a/examples/hlapi/v1arch/asyncio/manager/cmdgen/v1-get.py
+++ b/examples/hlapi/v1arch/asyncio/manager/cmdgen/v1-get.py
@@ -16,6 +16,7 @@ Functionally similar to:
 
 """#
 import asyncio
+
 from pysnmp.hlapi.v1arch.asyncio import *
 
 
diff --git a/pysnmp/cache.py b/pysnmp/cache.py
index f4b8796e..55521f96 100644
--- a/pysnmp/cache.py
+++ b/pysnmp/cache.py
@@ -10,36 +10,41 @@
 
 class Cache(object):
     def __init__(self, maxSize=256):
-        self.__maxSize = maxSize
-        self.__size = 0
-        self.__chopSize = maxSize // 10
-        self.__chopSize = self.__chopSize and self.__chopSize or 1
-        self.__cache = {}
-        self.__usage = {}
+        self._maxSize = maxSize
+        self._size = 0
+        self._chopSize = maxSize // 10
+        self._chopSize = self._chopSize or 1
+        self._cache = {}
+        self._usage = {}
 
     def __contains__(self, k):
-        return k in self.__cache
+        return k in self._cache
 
     def __getitem__(self, k):
-        self.__usage[k] += 1
-        return self.__cache[k]
+        self._usage[k] += 1
+        return self._cache[k]
 
     def __len__(self):
-        return self.__size
+        return self._size
 
     def __setitem__(self, k, v):
-        if self.__size >= self.__maxSize:
-            usageKeys = sorted(self.__usage, key=lambda x, d=self.__usage: d[x])
-            for _k in usageKeys[:self.__chopSize]:
-                del self.__cache[_k]
-                del self.__usage[_k]
-            self.__size -= self.__chopSize
-        if k not in self.__cache:
-            self.__size += 1
-            self.__usage[k] = 0
-        self.__cache[k] = v
+        if self._size >= self._maxSize:
+            usageKeys = sorted(
+                self._usage, key=lambda x, d=self._usage: d[x])
+
+            for _k in usageKeys[:self._chopSize]:
+                del self._cache[_k]
+                del self._usage[_k]
+
+            self._size -= self._chopSize
+
+        if k not in self._cache:
+            self._size += 1
+            self._usage[k] = 0
+
+        self._cache[k] = v
 
     def __delitem__(self, k):
-        del self.__cache[k]
-        del self.__usage[k]
-        self.__size -= 1
+        del self._cache[k]
+        del self._usage[k]
+        self._size -= 1
diff --git a/pysnmp/carrier/asyncio/base.py b/pysnmp/carrier/asyncio/base.py
index 4ee21ead..65be62ed 100644
--- a/pysnmp/carrier/asyncio/base.py
+++ b/pysnmp/carrier/asyncio/base.py
@@ -35,5 +35,5 @@ from pysnmp.carrier.base import AbstractTransport
 
 
 class AbstractAsyncioTransport(AbstractTransport):
-    PROTO_TRANSPORT_DISPATCHER = AsyncioDispatcher
     """Base Asyncio Transport, to be used with AsyncioDispatcher"""
+    PROTO_TRANSPORT_DISPATCHER = AsyncioDispatcher
diff --git a/pysnmp/carrier/asyncio/dgram/base.py b/pysnmp/carrier/asyncio/dgram/base.py
index ae5ab3a7..be91a983 100644
--- a/pysnmp/carrier/asyncio/dgram/base.py
+++ b/pysnmp/carrier/asyncio/dgram/base.py
@@ -57,27 +57,38 @@ class DgramAsyncioProtocol(asyncio.DatagramProtocol, AbstractAsyncioTransport):
     def __init__(self, sock=None, sockMap=None, loop=None):
         self._writeQ = []
         self._lport = None
+
         if loop is None:
             loop = asyncio.get_event_loop()
+
         self.loop = loop
 
     def datagram_received(self, datagram, transportAddress):
         if self._cbFun is None:
             raise error.CarrierError('Unable to call cbFun')
+
         else:
             self.loop.call_soon(self._cbFun, self, transportAddress, datagram)
 
     def connection_made(self, transport):
         self.transport = transport
+
         debug.logger & debug.FLAG_IO and debug.logger('connection_made: invoked')
+
         while self._writeQ:
             outgoingMessage, transportAddress = self._writeQ.pop(0)
-            debug.logger & debug.FLAG_IO and debug.logger('connection_made: transportAddress %r outgoingMessage %s' %
-                                                          (transportAddress, debug.hexdump(outgoingMessage)))
+
+            debug.logger & debug.FLAG_IO and debug.logger(
+                'connection_made: transportAddress %r outgoingMessage %s' % (
+                    transportAddress, debug.hexdump(outgoingMessage)))
+
             try:
-                self.transport.sendto(outgoingMessage, self.normalizeAddress(transportAddress))
+                self.transport.sendto(
+                    outgoingMessage, self.normalizeAddress(transportAddress))
+
             except Exception:
-                raise error.CarrierError(';'.join(traceback.format_exception(*sys.exc_info())))
+                raise error.CarrierError(
+                    ';'.join(traceback.format_exception(*sys.exc_info())))
 
     def connection_lost(self, exc):
         debug.logger & debug.FLAG_IO and debug.logger('connection_lost: invoked')
@@ -89,14 +100,17 @@ class DgramAsyncioProtocol(asyncio.DatagramProtocol, AbstractAsyncioTransport):
             c = self.loop.create_datagram_endpoint(
                 lambda: self, local_addr=iface, family=self.SOCK_FAMILY
             )
+
             # Avoid deprecation warning for asyncio.async()
             if IS_PYTHON_344_PLUS:
               self._lport = asyncio.ensure_future(c)
+
             else: # pragma: no cover
               self._lport = getattr(asyncio, 'async')(c)
 
         except Exception:
             raise error.CarrierError(';'.join(traceback.format_exception(*sys.exc_info())))
+
         return self
 
     def openServerMode(self, iface):
@@ -104,36 +118,48 @@ class DgramAsyncioProtocol(asyncio.DatagramProtocol, AbstractAsyncioTransport):
             c = self.loop.create_datagram_endpoint(
                 lambda: self, local_addr=iface, family=self.SOCK_FAMILY
             )
+
             # Avoid deprecation warning for asyncio.async()
             if IS_PYTHON_344_PLUS:
               self._lport = asyncio.ensure_future(c)
+
             else: # pragma: no cover
               self._lport = getattr(asyncio, 'async')(c)
+
         except Exception:
             raise error.CarrierError(';'.join(traceback.format_exception(*sys.exc_info())))
+
         return self
 
     def closeTransport(self):
         if self._lport is not None:
             self._lport.cancel()
+
         if self.transport is not None:
             self.transport.close()
+
         AbstractAsyncioTransport.closeTransport(self)
 
     def sendMessage(self, outgoingMessage, transportAddress):
-        debug.logger & debug.FLAG_IO and debug.logger('sendMessage: %s transportAddress %r outgoingMessage %s' % (
-            (self.transport is None and "queuing" or "sending"),
-            transportAddress, debug.hexdump(outgoingMessage)
-        ))
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'sendMessage: %s transportAddress %r outgoingMessage '
+            '%s' % (self.transport is None and "queuing" or "sending",
+                    transportAddress, debug.hexdump(outgoingMessage)))
+
         if self.transport is None:
             self._writeQ.append((outgoingMessage, transportAddress))
+
         else:
             try:
-                self.transport.sendto(outgoingMessage, self.normalizeAddress(transportAddress))
+                self.transport.sendto(
+                    outgoingMessage, self.normalizeAddress(transportAddress))
+
             except Exception:
-                raise error.CarrierError(';'.join(traceback.format_exception(*sys.exc_info())))
+                raise error.CarrierError(
+                    ';'.join(traceback.format_exception(*sys.exc_info())))
 
     def normalizeAddress(self, transportAddress):
         if not isinstance(transportAddress, self.ADDRESS_TYPE):
             transportAddress = self.ADDRESS_TYPE(transportAddress)
+
         return transportAddress
diff --git a/pysnmp/carrier/asyncio/dispatch.py b/pysnmp/carrier/asyncio/dispatch.py
index cb9f2020..2fd7d86e 100644
--- a/pysnmp/carrier/asyncio/dispatch.py
+++ b/pysnmp/carrier/asyncio/dispatch.py
@@ -34,24 +34,29 @@ import platform
 import sys
 import traceback
 
-from pysnmp.carrier.base import AbstractTransportDispatcher
-from pysnmp.error import PySnmpError
-
 try:
     import asyncio
+
 except ImportError:
     import trollius as asyncio
 
+from pysnmp.carrier.base import AbstractTransportDispatcher
+from pysnmp.error import PySnmpError
+
 IS_PYTHON_344_PLUS = platform.python_version_tuple() >= ('3', '4', '4')
 
+
 class AsyncioDispatcher(AbstractTransportDispatcher):
     """AsyncioDispatcher based on asyncio event loop"""
 
     def __init__(self, *args, **kwargs):
         AbstractTransportDispatcher.__init__(self)
+
         self.__transportCount = 0
+
         if 'timeout' in kwargs:
             self.setTimerResolution(kwargs['timeout'])
+
         self.loopingcall = None
         self.loop = kwargs.pop('loop', asyncio.get_event_loop())
 
@@ -65,25 +70,32 @@ class AsyncioDispatcher(AbstractTransportDispatcher):
         if not self.loop.is_running():
             try:
                 self.loop.run_forever()
+
             except KeyboardInterrupt:
                 raise
+
             except Exception:
-                raise PySnmpError(';'.join(traceback.format_exception(*sys.exc_info())))
+                raise PySnmpError(
+                    ';'.join(traceback.format_exception(*sys.exc_info())))
 
     def registerTransport(self, tDomain, transport):
         if self.loopingcall is None and self.getTimerResolution() > 0:
             # Avoid deprecation warning for asyncio.async()
             if IS_PYTHON_344_PLUS:
-              self.loopingcall = asyncio.ensure_future(self.handle_timeout())
-            else: # pragma: no cover
-              self.loopingcall = getattr(asyncio, 'async')(self.handle_timeout())
+                self.loopingcall = asyncio.ensure_future(self.handle_timeout())
+
+            else:
+                self.loopingcall = getattr(asyncio, 'async')(self.handle_timeout())
+
         AbstractTransportDispatcher.registerTransport(
             self, tDomain, transport
         )
+
         self.__transportCount += 1
 
     def unregisterTransport(self, tDomain):
         t = AbstractTransportDispatcher.getTransport(self, tDomain)
+
         if t is not None:
             AbstractTransportDispatcher.unregisterTransport(self, tDomain)
             self.__transportCount -= 1
diff --git a/pysnmp/carrier/asyncore/base.py b/pysnmp/carrier/asyncore/base.py
index f7b1af9e..3fa13290 100644
--- a/pysnmp/carrier/asyncore/base.py
+++ b/pysnmp/carrier/asyncore/base.py
@@ -24,17 +24,21 @@ class AbstractSocketTransport(asyncore.dispatcher, AbstractTransport):
     # noinspection PyUnusedLocal
     def __init__(self, sock=None, sockMap=None):
         asyncore.dispatcher.__init__(self)
+
         if sock is None:
             if self.SOCK_FAMILY is None:
                 raise error.CarrierError(
                     'Address family %s not supported' % self.__class__.__name__
                 )
+
             if self.SOCK_TYPE is None:
                 raise error.CarrierError(
                     'Socket type %s not supported' % self.__class__.__name__
                 )
+
             try:
                 sock = socket.socket(self.SOCK_FAMILY, self.SOCK_TYPE)
+
             except socket.error as exc:
                 raise error.CarrierError('socket() failed: %s' % exc)
 
@@ -43,9 +47,16 @@ class AbstractSocketTransport(asyncore.dispatcher, AbstractTransport):
                     bsize = sock.getsockopt(socket.SOL_SOCKET, b)
                     if bsize < self.BUFFER_SIZE:
                         sock.setsockopt(socket.SOL_SOCKET, b, self.BUFFER_SIZE)
-                        debug.logger & debug.FLAG_IO and debug.logger('%s: socket %d buffer size increased from %d to %d for buffer %d' % (self.__class__.__name__, sock.fileno(), bsize, self.BUFFER_SIZE, b))
+                        debug.logger & debug.FLAG_IO and debug.logger(
+                            '%s: socket %d buffer size increased from %d to %d '
+                            'for buffer %d' % (
+                                self.__class__.__name__, sock.fileno(),
+                                bsize, self.BUFFER_SIZE, b))
+
             except Exception as exc:
-                debug.logger & debug.FLAG_IO and debug.logger('%s: socket buffer size option mangling failure for buffer: %s' % (self.__class__.__name__, exc))
+                debug.logger & debug.FLAG_IO and debug.logger(
+                    '%s: socket buffer size option mangling failure for buffer: '
+                    '%s' % (self.__class__.__name__, exc))
 
         # The socket map is managed by the AsyncoreDispatcher on
         # which this transport is registered. Here we just prepare
@@ -54,6 +65,7 @@ class AbstractSocketTransport(asyncore.dispatcher, AbstractTransport):
 
         sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
         sock.setblocking(0)
+
         self.set_socket(sock)
 
     def __hash__(self):
@@ -61,16 +73,6 @@ class AbstractSocketTransport(asyncore.dispatcher, AbstractTransport):
 
     # The following two methods are part of base class so here we overwrite
     # them to separate socket management from dispatcher registration tasks.
-    # These two are just for dispatcher registration.
-    def add_channel(self, map=None):
-        if map is not None:
-            map[self._fileno] = self
-            self.connected = True
-
-    def del_channel(self, map=None):
-        if map is not None and self._fileno in map:
-            del map[self._fileno]
-            self.connected = False
 
     def registerSocket(self, sockMap=None):
         self.add_channel(sockMap)
@@ -84,6 +86,18 @@ class AbstractSocketTransport(asyncore.dispatcher, AbstractTransport):
 
     # asyncore API
 
+    # The first two methods are just for dispatcher registration
+
+    def add_channel(self, map=None):
+        if map is not None:
+            map[self._fileno] = self
+            self.connected = True
+
+    def del_channel(self, map=None):
+        if map is not None and self._fileno in map:
+            del map[self._fileno]
+            self.connected = False
+
     def handle_close(self):
         raise error.CarrierError('Transport unexpectedly closed')
 
diff --git a/pysnmp/carrier/asyncore/dgram/base.py b/pysnmp/carrier/asyncore/dgram/base.py
index e456da20..06453096 100644
--- a/pysnmp/carrier/asyncore/dgram/base.py
+++ b/pysnmp/carrier/asyncore/dgram/base.py
@@ -47,16 +47,20 @@ class DgramSocketTransport(AbstractSocketTransport):
         if iface is not None:
             try:
                 self.socket.bind(iface)
+
             except socket.error as exc:
-                raise error.CarrierError(
-                    'bind() for %s failed: %s' % (iface is None and "<all local>" or iface, exc))
+                raise error.CarrierError('bind() for %s failed: %s' % (
+                    iface is None and "<all local>" or iface, exc))
+
         return self
 
     def openServerMode(self, iface):
         try:
             self.socket.bind(iface)
+
         except socket.error as exc:
             raise error.CarrierError('bind() for %s failed: %s' % (iface, exc))
+
         return self
 
     def enableBroadcast(self, flag=1):
@@ -64,30 +68,47 @@ class DgramSocketTransport(AbstractSocketTransport):
             self.socket.setsockopt(
                 socket.SOL_SOCKET, socket.SO_BROADCAST, flag
             )
+
         except socket.error as exc:
-            raise error.CarrierError('setsockopt() for SO_BROADCAST failed: %s' % exc)
-        debug.logger & debug.FLAG_IO and debug.logger('enableBroadcast: %s option SO_BROADCAST on socket %s' % (flag and "enabled" or "disabled", self.socket.fileno()))
+            raise error.CarrierError('setsockopt() for SO_BROADCAST '
+                                     'failed: %s' % exc)
+
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'enableBroadcast: %s option SO_BROADCAST on '
+            'socket %s' % (flag and "enabled" or "disabled", self.socket.fileno()))
+
         return self
 
     def enablePktInfo(self, flag=1):
         if (not hasattr(self.socket, 'sendmsg') or
                 not hasattr(self.socket, 'recvmsg')):
-            raise error.CarrierError('sendmsg()/recvmsg() interface is not supported by this OS and/or Python version')
+            raise error.CarrierError(
+                'sendmsg()/recvmsg() interface is not supported by this OS '
+                'and/or Python version')
 
         try:
             if self.socket.family == socket.AF_INET:
                 self.socket.setsockopt(socket.SOL_IP, socket.IP_PKTINFO, flag)
 
             if self.socket.family == socket.AF_INET6:
-                self.socket.setsockopt(socket.SOL_IPV6, socket.IPV6_RECVPKTINFO, flag)
+                self.socket.setsockopt(
+                    socket.SOL_IPV6, socket.IPV6_RECVPKTINFO, flag)
 
         except socket.error as exc:
-            raise error.CarrierError('setsockopt() for %s failed: %s' % (self.socket.family == socket.AF_INET6 and "IPV6_RECVPKTINFO" or "IP_PKTINFO", exc))
+            raise error.CarrierError(
+                'setsockopt() for %s failed: '
+                '%s' % (self.socket.family == socket.AF_INET6 and
+                        "IPV6_RECVPKTINFO" or "IP_PKTINFO", exc))
 
         self._sendto = sockmsg.getSendTo(self.ADDRESS_TYPE)
         self._recvfrom = sockmsg.getRecvFrom(self.ADDRESS_TYPE)
 
-        debug.logger & debug.FLAG_IO and debug.logger('enablePktInfo: %s option %s on socket %s' % (self.socket.family == socket.AF_INET6 and "IPV6_RECVPKTINFO" or "IP_PKTINFO", flag and "enabled" or "disabled", self.socket.fileno()))
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'enablePktInfo: %s option %s on socket '
+            '%s' % (self.socket.family == socket.AF_INET6 and "IPV6_RECVPKTINFO"
+                    or "IP_PKTINFO", flag and "enabled" or "disabled",
+                    self.socket.fileno()))
+
         return self
 
     def enableTransparent(self, flag=1):
@@ -96,25 +117,34 @@ class DgramSocketTransport(AbstractSocketTransport):
                 self.socket.setsockopt(
                     socket.SOL_IP, socket.IP_TRANSPARENT, flag
                 )
+
             if self.socket.family == socket.AF_INET6:
                 self.socket.setsockopt(
                     socket.SOL_IPV6, socket.IPV6_TRANSPARENT, flag
                 )
 
         except socket.error as exc:
-            raise error.CarrierError('setsockopt() for IP_TRANSPARENT failed: %s' % exc)
+            raise error.CarrierError('setsockopt() for IP_TRANSPARENT '
+                                     'failed: %s' % exc)
 
         except OSError:
-            raise error.CarrierError('IP_TRANSPARENT socket option requires superuser priveleges')
+            raise error.CarrierError('IP_TRANSPARENT socket option requires '
+                                     'superuser privileges')
+
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'enableTransparent: %s option IP_TRANSPARENT on socket '
+            '%s' % (flag and "enabled" or "disabled", self.socket.fileno()))
 
-        debug.logger & debug.FLAG_IO and debug.logger('enableTransparent: %s option IP_TRANSPARENT on socket %s' % (flag and "enabled" or "disabled", self.socket.fileno()))
         return self
 
     def sendMessage(self, outgoingMessage, transportAddress):
         self.__outQueue.append(
             (outgoingMessage, self.normalizeAddress(transportAddress))
         )
-        debug.logger & debug.FLAG_IO and debug.logger('sendMessage: outgoingMessage queued (%d octets) %s' % (len(outgoingMessage), debug.hexdump(outgoingMessage)))
+
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'sendMessage: outgoingMessage queued (%d octets) %s' % (
+                len(outgoingMessage), debug.hexdump(outgoingMessage)))
 
     def normalizeAddress(self, transportAddress):
         if not isinstance(transportAddress, self.ADDRESS_TYPE):
@@ -134,6 +164,7 @@ class DgramSocketTransport(AbstractSocketTransport):
             return '0.0.0.0', 0
 
     # asyncore API
+
     def handle_connect(self):
         pass
 
@@ -142,40 +173,58 @@ class DgramSocketTransport(AbstractSocketTransport):
 
     def handle_write(self):
         outgoingMessage, transportAddress = self.__outQueue.pop(0)
-        debug.logger & debug.FLAG_IO and debug.logger('handle_write: transportAddress %r -> %r outgoingMessage (%d octets) %s' % (transportAddress.getLocalAddress(), transportAddress, len(outgoingMessage), debug.hexdump(outgoingMessage)))
+
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'handle_write: transportAddress %r -> %r outgoingMessage (%d '
+            'octets) %s' % (transportAddress.getLocalAddress(), transportAddress,
+                            len(outgoingMessage), debug.hexdump(outgoingMessage)))
+
         if not transportAddress:
-            debug.logger & debug.FLAG_IO and debug.logger('handle_write: missing dst address, loosing outgoing msg')
+            debug.logger & debug.FLAG_IO and debug.logger(
+                'handle_write: missing dst address, loosing outgoing msg')
             return
+
         try:
-            self._sendto(
-                self.socket, outgoingMessage, transportAddress
-            )
+            self._sendto(self.socket, outgoingMessage, transportAddress)
+
         except socket.error as exc:
             if exc.args[0] in SOCK_ERRORS:
-                debug.logger & debug.FLAG_IO and debug.logger('handle_write: ignoring socket error %s' % exc)
+                debug.logger & debug.FLAG_IO and debug.logger(
+                    'handle_write: ignoring socket error %s' % exc)
+
             else:
-                raise error.CarrierError('sendto() failed for %s: %s' % (transportAddress, exc))
+                raise error.CarrierError(
+                    'sendto() failed for %s: %s' % (transportAddress, exc))
 
     def readable(self):
-        return 1
+        return True
 
     def handle_read(self):
         try:
             incomingMessage, transportAddress = self._recvfrom(self.socket, 65535)
+
             transportAddress = self.normalizeAddress(transportAddress)
+
             debug.logger & debug.FLAG_IO and debug.logger(
-                'handle_read: transportAddress %r -> %r incomingMessage (%d octets) %s' % (transportAddress, transportAddress.getLocalAddress(), len(incomingMessage), debug.hexdump(incomingMessage)))
+                'handle_read: transportAddress %r -> %r incomingMessage (%d '
+                'octets) %s' % (transportAddress, transportAddress.getLocalAddress(),
+                                len(incomingMessage), debug.hexdump(incomingMessage)))
+
             if not incomingMessage:
                 self.handle_close()
                 return
+
             else:
                 self._cbFun(self, transportAddress, incomingMessage)
                 return
+
         except socket.error as exc:
             if exc.args[0] in SOCK_ERRORS:
-                debug.logger & debug.FLAG_IO and debug.logger('handle_read: known socket error %s' % exc)
+                debug.logger & debug.FLAG_IO and debug.logger(
+                    'handle_read: known socket error %s' % exc)
                 SOCK_ERRORS[exc.args[0]] and self.handle_close()
                 return
+
             else:
                 raise error.CarrierError('recvfrom() failed: %s' % exc)
 
diff --git a/pysnmp/carrier/asyncore/dgram/udp6.py b/pysnmp/carrier/asyncore/dgram/udp6.py
index 75d348d6..3207c6ff 100644
--- a/pysnmp/carrier/asyncore/dgram/udp6.py
+++ b/pysnmp/carrier/asyncore/dgram/udp6.py
@@ -22,17 +22,18 @@ class Udp6SocketTransport(DgramSocketTransport):
 
     def normalizeAddress(self, transportAddress):
         if '%' in transportAddress[0]:  # strip zone ID
-            ta = self.ADDRESS_TYPE((transportAddress[0].split('%')[0],
-                                    transportAddress[1],
-                                    0,  # flowinfo
-                                    0))  # scopeid
+            ta = self.ADDRESS_TYPE(
+                (transportAddress[0].split('%')[0], transportAddress[1], 0, 0))
+
         else:
-            ta = self.ADDRESS_TYPE((transportAddress[0],
-                                    transportAddress[1], 0, 0))
+            ta = self.ADDRESS_TYPE(
+                (transportAddress[0], transportAddress[1], 0, 0))
 
         if (isinstance(transportAddress, self.ADDRESS_TYPE) and
                 transportAddress.getLocalAddress()):
+
             return ta.setLocalAddress(transportAddress.getLocalAddress())
+
         else:
             return ta.setLocalAddress(self.getLocalAddress())
 
diff --git a/pysnmp/carrier/asyncore/dgram/unix.py b/pysnmp/carrier/asyncore/dgram/unix.py
index 0f68f962..b5233844 100644
--- a/pysnmp/carrier/asyncore/dgram/unix.py
+++ b/pysnmp/carrier/asyncore/dgram/unix.py
@@ -9,6 +9,7 @@ import random
 
 try:
     from socket import AF_UNIX
+
 except ImportError:
     AF_UNIX = None
 
@@ -33,14 +34,20 @@ class UnixSocketTransport(DgramSocketTransport):
         if iface is None:
             # UNIX domain sockets must be explicitly bound
             iface = ''
+
             while len(iface) < 8:
                 iface += chr(random.randrange(65, 91))
                 iface += chr(random.randrange(97, 123))
-            iface = os.path.sep + 'tmp' + os.path.sep + 'pysnmp' + iface
+
+            iface = os.path.join(os.path.sep, 'tmp', 'pysnmp', iface)
+
         if os.path.exists(iface):
             os.remove(iface)
+
         DgramSocketTransport.openClientMode(self, iface)
+
         self._iface = iface
+
         return self
 
     def openServerMode(self, iface):
@@ -50,8 +57,10 @@ class UnixSocketTransport(DgramSocketTransport):
 
     def closeTransport(self):
         DgramSocketTransport.closeTransport(self)
+
         try:
             os.remove(self._iface)
+
         except OSError:
             pass
 
diff --git a/pysnmp/carrier/asyncore/dispatch.py b/pysnmp/carrier/asyncore/dispatch.py
index 897fdd0c..3f448471 100644
--- a/pysnmp/carrier/asyncore/dispatch.py
+++ b/pysnmp/carrier/asyncore/dispatch.py
@@ -16,7 +16,8 @@ from pysnmp.error import PySnmpError
 
 class AsyncoreDispatcher(AbstractTransportDispatcher):
     def __init__(self):
-        self.__sockMap = {}  # use own map for MT safety
+        # use own map for MT safety
+        self.__sockMap = {}
         AbstractTransportDispatcher.__init__(self)
 
     def getSocketMap(self):
@@ -25,13 +26,14 @@ class AsyncoreDispatcher(AbstractTransportDispatcher):
     def setSocketMap(self, sockMap=socket_map):
         self.__sockMap = sockMap
 
-    def registerTransport(self, tDomain, t):
-        AbstractTransportDispatcher.registerTransport(self, tDomain, t)
-        t.registerSocket(self.__sockMap)
+    def registerTransport(self, transportDomain, transport):
+        AbstractTransportDispatcher.registerTransport(
+            self, transportDomain, transport)
+        transport.registerSocket(self.__sockMap)
 
-    def unregisterTransport(self, tDomain):
-        self.getTransport(tDomain).unregisterSocket(self.__sockMap)
-        AbstractTransportDispatcher.unregisterTransport(self, tDomain)
+    def unregisterTransport(self, transportDomain):
+        self.getTransport(transportDomain).unregisterSocket(self.__sockMap)
+        AbstractTransportDispatcher.unregisterTransport(self, transportDomain)
 
     def transportsAreWorking(self):
         for transport in self.__sockMap.values():
@@ -43,9 +45,12 @@ class AsyncoreDispatcher(AbstractTransportDispatcher):
             try:
                 loop(timeout or self.getTimerResolution(),
                      use_poll=True, map=self.__sockMap, count=1)
+
             except KeyboardInterrupt:
                 raise
 
             except Exception:
-                raise PySnmpError('poll error: %s' % ';'.join(format_exception(*exc_info())))
+                raise PySnmpError(
+                    'poll error: %s' % ';'.join(format_exception(*exc_info())))
+
             self.handleTimerTick(time())
diff --git a/pysnmp/carrier/base.py b/pysnmp/carrier/base.py
index 12dfc86b..518f304b 100644
--- a/pysnmp/carrier/base.py
+++ b/pysnmp/carrier/base.py
@@ -53,6 +53,7 @@ class AbstractTransportDispatcher(object):
     def _cbFun(self, incomingTransport, transportAddress, incomingMessage):
         if incomingTransport in self.__transportDomainMap:
             transportDomain = self.__transportDomainMap[incomingTransport]
+
         else:
             raise error.CarrierError(
                 'Unregistered transport %s' % (incomingTransport,)
@@ -62,6 +63,7 @@ class AbstractTransportDispatcher(object):
             recvId = self.__routingCbFun(
                 transportDomain, transportAddress, incomingMessage
             )
+
         else:
             recvId = None
 
@@ -69,6 +71,7 @@ class AbstractTransportDispatcher(object):
             self.__recvCallables[recvId](
                 self, transportDomain, transportAddress, incomingMessage
             )
+
         else:
             raise error.CarrierError(
                 'No callback for "%r" found - loosing incoming event' % (recvId,)
@@ -81,6 +84,7 @@ class AbstractTransportDispatcher(object):
             raise error.CarrierError(
                 'Data routing callback already registered'
             )
+
         self.__routingCbFun = routingCbFun
 
     def unregisterRoutingCbFun(self):
@@ -92,6 +96,7 @@ class AbstractTransportDispatcher(object):
             raise error.CarrierError(
                 'Receive callback %r already registered' % (recvId is None and '<default>' or recvId,)
             )
+
         self.__recvCallables[recvId] = recvCb
 
     def unregisterRecvCbFun(self, recvId=None):
@@ -101,38 +106,44 @@ class AbstractTransportDispatcher(object):
     def registerTimerCbFun(self, timerCbFun, tickInterval=None):
         if not tickInterval:
             tickInterval = self.__timerResolution
+
         self.__timerCallables.append(TimerCallable(timerCbFun, tickInterval))
 
     def unregisterTimerCbFun(self, timerCbFun=None):
         if timerCbFun:
             self.__timerCallables.remove(timerCbFun)
+
         else:
             self.__timerCallables = []
 
-    def registerTransport(self, tDomain, transport):
-        if tDomain in self.__transports:
+    def registerTransport(self, transportDomain, transport):
+        if transportDomain in self.__transports:
             raise error.CarrierError(
-                'Transport %s already registered' % (tDomain,)
+                'Transport %s already registered' % (transportDomain,)
             )
+
         transport.registerCbFun(self._cbFun)
-        self.__transports[tDomain] = transport
-        self.__transportDomainMap[transport] = tDomain
 
-    def unregisterTransport(self, tDomain):
-        if tDomain not in self.__transports:
+        self.__transports[transportDomain] = transport
+        self.__transportDomainMap[transport] = transportDomain
+
+    def unregisterTransport(self, transportDomain):
+        if transportDomain not in self.__transports:
             raise error.CarrierError(
-                'Transport %s not registered' % (tDomain,)
+                'Transport %s not registered' % (transportDomain,)
             )
-        self.__transports[tDomain].unregisterCbFun()
-        del self.__transportDomainMap[self.__transports[tDomain]]
-        del self.__transports[tDomain]
+
+        self.__transports[transportDomain].unregisterCbFun()
+
+        del self.__transportDomainMap[self.__transports[transportDomain]]
+        del self.__transports[transportDomain]
 
     def getTransport(self, transportDomain):
         if transportDomain in self.__transports:
             return self.__transports[transportDomain]
+
         raise error.CarrierError(
-            'Transport %s not registered' % (transportDomain,)
-        )
+            'Transport %s not registered' % (transportDomain,))
 
     def sendMessage(self, outgoingMessage, transportDomain,
                     transportAddress):
@@ -140,10 +151,10 @@ class AbstractTransportDispatcher(object):
             self.__transports[transportDomain].sendMessage(
                 outgoingMessage, transportAddress
             )
+
         else:
-            raise error.CarrierError(
-                'No suitable transport domain for %s' % (transportDomain,)
-            )
+            raise error.CarrierError('No suitable transport domain for '
+                                     '%s' % (transportDomain,))
 
     def getTimerResolution(self):
         return self.__timerResolution
@@ -151,6 +162,7 @@ class AbstractTransportDispatcher(object):
     def setTimerResolution(self, timerResolution):
         if timerResolution < 0.01 or timerResolution > 10:
             raise error.CarrierError('Impossible timer resolution')
+
         self.__timerResolution = timerResolution
         self.__timerDelta = timerResolution * 0.05
 
@@ -173,6 +185,7 @@ class AbstractTransportDispatcher(object):
     def jobStarted(self, jobId, count=1):
         if jobId in self.__jobs:
             self.__jobs[jobId] += count
+
         else:
             self.__jobs[jobId] = count
 
@@ -191,6 +204,7 @@ class AbstractTransportDispatcher(object):
         for tDomain in list(self.__transports):
             self.__transports[tDomain].closeTransport()
             self.unregisterTransport(tDomain)
+
         self.__transports.clear()
         self.unregisterRecvCbFun()
         self.unregisterTimerCbFun()
@@ -207,7 +221,8 @@ class AbstractTransportAddress(object):
         return self._localAddress
 
     def clone(self, localAddress=None):
-        return self.__class__(self).setLocalAddress(localAddress is None and self.getLocalAddress() or localAddress)
+        return self.__class__(self).setLocalAddress(
+            localAddress is None and self.getLocalAddress() or localAddress)
 
 
 class AbstractTransport(object):
@@ -221,9 +236,8 @@ class AbstractTransport(object):
 
     def registerCbFun(self, cbFun):
         if self._cbFun:
-            raise error.CarrierError(
-                'Callback function %s already registered at %s' % (self._cbFun, self)
-            )
+            raise error.CarrierError('Callback function %s already registered '
+                                     'at %s' % (self._cbFun, self))
         self._cbFun = cbFun
 
     def unregisterCbFun(self):
diff --git a/pysnmp/carrier/sockmsg.py b/pysnmp/carrier/sockmsg.py
index e36bc85a..6249b79d 100644
--- a/pysnmp/carrier/sockmsg.py
+++ b/pysnmp/carrier/sockmsg.py
@@ -21,11 +21,13 @@ from pysnmp import debug
 
 if sys.version_info[:2] < (3, 3):
     def getRecvFrom(addressType):
-        raise error.CarrierError('sendmsg()/recvmsg() interface is not supported by this OS and/or Python version')
+        raise error.CarrierError('sendmsg()/recvmsg() interface is not '
+                                 'supported by this OS and/or Python version')
 
 
     def getSendTo(addressType):
-        raise error.CarrierError('sendmsg()/recvmsg() interface is not supported by this OS and/or Python version')
+        raise error.CarrierError('sendmsg()/recvmsg() interface is not '
+                                 'supported by this OS and/or Python version')
 
 else:
     import ctypes
@@ -82,13 +84,13 @@ else:
                 if anc[0] == socket.SOL_IP and anc[1] == socket.IP_PKTINFO:
                     addr = in_pktinfo.from_buffer_copy(anc[2])
                     addr = ipaddress.IPv4Address(memoryview(addr.ipi_addr).tobytes())
-                    _to = (str(addr), s.getsockname()[1])
+                    _to = str(addr), s.getsockname()[1]
                     break
 
                 elif anc[0] == socket.SOL_IPV6 and anc[1] == socket.IPV6_PKTINFO:
                     addr = in6_pktinfo.from_buffer_copy(anc[2])
                     addr = ipaddress.ip_address(memoryview(addr.ipi6_addr).tobytes())
-                    _to = (str(addr), s.getsockname()[1])
+                    _to = str(addr), s.getsockname()[1]
                     break
 
             debug.logger & debug.FLAG_IO and debug.logger(
diff --git a/pysnmp/carrier/twisted/dgram/base.py b/pysnmp/carrier/twisted/dgram/base.py
index c752e580..eddd5a76 100644
--- a/pysnmp/carrier/twisted/dgram/base.py
+++ b/pysnmp/carrier/twisted/dgram/base.py
@@ -18,8 +18,9 @@ class DgramTwistedTransport(DatagramProtocol, AbstractTwistedTransport):
     # Twisted Datagram API
 
     def datagramReceived(self, datagram, transportAddress):
-        if self._cbFun is None:
+        if not self._cbFun:
             raise error.CarrierError('Unable to call cbFun')
+
         else:
             # Callback fun is called through callLater() in attempt
             # to make Twisted timed calls work under high load.
@@ -27,11 +28,16 @@ class DgramTwistedTransport(DatagramProtocol, AbstractTwistedTransport):
 
     def startProtocol(self):
         debug.logger & debug.FLAG_IO and debug.logger('startProtocol: invoked')
+
         while self._writeQ:
             outgoingMessage, transportAddress = self._writeQ.pop(0)
-            debug.logger & debug.FLAG_IO and debug.logger('startProtocol: transportAddress %r outgoingMessage %s' % (transportAddress, debug.hexdump(outgoingMessage)))
+            debug.logger & debug.FLAG_IO and debug.logger(
+                'startProtocol: transportAddress %r outgoingMessage '
+                '%s' % (transportAddress, debug.hexdump(outgoingMessage)))
+
             try:
                 self.transport.write(outgoingMessage, transportAddress)
+
             except Exception as exc:
                 raise error.CarrierError('Twisted exception: %s' % exc)
 
@@ -39,11 +45,17 @@ class DgramTwistedTransport(DatagramProtocol, AbstractTwistedTransport):
         debug.logger & debug.FLAG_IO and debug.logger('stopProtocol: invoked')
 
     def sendMessage(self, outgoingMessage, transportAddress):
-        debug.logger & debug.FLAG_IO and debug.logger('startProtocol: %s transportAddress %r outgoingMessage %s' % ((self.transport is None and "queuing" or "sending"), transportAddress, debug.hexdump(outgoingMessage)))
-        if self.transport is None:
+        debug.logger & debug.FLAG_IO and debug.logger(
+            'startProtocol: %s transportAddress %r outgoingMessage '
+            '%s' % ((self.transport is None and "queuing" or "sending"),
+                    transportAddress, debug.hexdump(outgoingMessage)))
+
+        if not self.transport:
             self._writeQ.append((outgoingMessage, transportAddress))
+
         else:
             try:
                 self.transport.write(outgoingMessage, transportAddress)
+
             except Exception as exc:
                 raise error.CarrierError('Twisted exception: %s' % exc)
diff --git a/pysnmp/carrier/twisted/dgram/udp.py b/pysnmp/carrier/twisted/dgram/udp.py
index 10cf946f..2057c97d 100644
--- a/pysnmp/carrier/twisted/dgram/udp.py
+++ b/pysnmp/carrier/twisted/dgram/udp.py
@@ -26,24 +26,30 @@ class UdpTwistedTransport(DgramTwistedTransport):
     def openClientMode(self, iface=None):
         if iface is None:
             iface = ('', 0)
+
         try:
             self._lport = reactor.listenUDP(iface[1], self, iface[0])
+
         except Exception as exc:
             raise error.CarrierError(exc)
+
         return self
 
     def openServerMode(self, iface):
         try:
             self._lport = reactor.listenUDP(iface[1], self, iface[0])
+
         except Exception as exc:
             raise error.CarrierError(exc)
+
         return self
 
     def closeTransport(self):
         if self._lport is not None:
-            d = self._lport.stopListening()
-            if d:
-                d.addCallback(lambda x: None)
+            deferred = self._lport.stopListening()
+            if deferred:
+                deferred.addCallback(lambda x: None)
+
             DgramTwistedTransport.closeTransport(self)
 
 
diff --git a/pysnmp/carrier/twisted/dgram/unix.py b/pysnmp/carrier/twisted/dgram/unix.py
index 6ce3cde2..2d5aa195 100644
--- a/pysnmp/carrier/twisted/dgram/unix.py
+++ b/pysnmp/carrier/twisted/dgram/unix.py
@@ -26,13 +26,16 @@ class UnixTwistedTransport(DgramTwistedTransport):
     def openClientMode(self, iface=''):
         try:
             self._lport = reactor.connectUNIXDatagram(iface, self)
+
         except Exception as exc:
             raise error.CarrierError(exc)
+
         return self
 
     def openServerMode(self, iface):
         try:
             self._lport = reactor.listenUNIXDatagram(iface, self)
+
         except Exception as exc:
             raise error.CarrierError(exc)
 
@@ -40,9 +43,10 @@ class UnixTwistedTransport(DgramTwistedTransport):
 
     def closeTransport(self):
         if self._lport is not None:
-            d = self._lport.stopListening()
-            if d:
-                d.addCallback(lambda x: None)
+            deferred = self._lport.stopListening()
+            if deferred:
+                deferred.addCallback(lambda x: None)
+
         DgramTwistedTransport.closeTransport(self)
 
 
diff --git a/pysnmp/carrier/twisted/dispatch.py b/pysnmp/carrier/twisted/dispatch.py
index 77f5c168..ace0f6a4 100644
--- a/pysnmp/carrier/twisted/dispatch.py
+++ b/pysnmp/carrier/twisted/dispatch.py
@@ -28,9 +28,12 @@ class TwistedDispatcher(AbstractTransportDispatcher):
 
     def __init__(self, *args, **kwargs):
         AbstractTransportDispatcher.__init__(self)
+
         self.__transportCount = 0
+
         if 'timeout' in kwargs:
             self.setTimerResolution(kwargs['timeout'])
+
         self.loopingcall = task.LoopingCall(
             lambda self=self: self.handleTimerTick(time.time())
         )
@@ -44,22 +47,27 @@ class TwistedDispatcher(AbstractTransportDispatcher):
                 raise
 
             except Exception:
-                raise PySnmpError('reactor error: %s' % ';'.join(traceback.format_exception(*sys.exc_info())))
+                raise PySnmpError('reactor error: %s' % ';'.join(
+                    traceback.format_exception(*sys.exc_info())))
 
     # jobstarted/jobfinished might be okay as-is
 
-    def registerTransport(self, tDomain, transport):
+    def registerTransport(self, transportDomain, transport):
         if not self.loopingcall.running and self.getTimerResolution() > 0:
             self.loopingcall.start(self.getTimerResolution(), now=False)
+
         AbstractTransportDispatcher.registerTransport(
-            self, tDomain, transport
+            self, transportDomain, transport
         )
+
         self.__transportCount += 1
 
-    def unregisterTransport(self, tDomain):
-        t = AbstractTransportDispatcher.getTransport(self, tDomain)
-        if t is not None:
-            AbstractTransportDispatcher.unregisterTransport(self, tDomain)
+    def unregisterTransport(self, transportDomain):
+        transport = AbstractTransportDispatcher.getTransport(
+            self, transportDomain)
+        if transport:
+            AbstractTransportDispatcher.unregisterTransport(
+                self, transportDomain)
             self.__transportCount -= 1
 
         # The last transport has been removed, stop the timeout
diff --git a/pysnmp/debug.py b/pysnmp/debug.py
index f6e69c79..e0e53607 100644
--- a/pysnmp/debug.py
+++ b/pysnmp/debug.py
@@ -43,14 +43,20 @@ class Printer(object):
     def __init__(self, logger=None, handler=None, formatter=None):
         if logger is None:
             logger = logging.getLogger('pysnmp')
+
         logger.setLevel(logging.DEBUG)
+
         if handler is None:
             handler = logging.StreamHandler()
+
         if formatter is None:
             formatter = logging.Formatter('%(asctime)s %(name)s: %(message)s')
+
         handler.setFormatter(formatter)
         handler.setLevel(logging.DEBUG)
+
         logger.addHandler(handler)
+
         self.__logger = logger
 
     def __call__(self, msg):
@@ -64,7 +70,7 @@ if hasattr(logging, 'NullHandler'):
     NullHandler = logging.NullHandler
 
 else:
-    # Python 2.6 and older
+    # Python 2.6
     class NullHandler(logging.Handler):
         def emit(self, record):
             pass
@@ -75,33 +81,42 @@ class Debug(object):
 
     def __init__(self, *flags, **options):
         self._flags = FLAG_NONE
+
         if options.get('printer') is not None:
             self._printer = options.get('printer')
+
         elif self.DEFAULT_PRINTER is not None:
             self._printer = self.DEFAULT_PRINTER
+
         else:
             if 'loggerName' in options:
                 # route our logs to parent logger
                 self._printer = Printer(
                     logger=logging.getLogger(options['loggerName']),
-                    handler=NullHandler()
-                )
+                    handler=NullHandler())
+
             else:
                 self._printer = Printer()
+
         self('running pysnmp version %s' % __version__)
-        for f in flags:
-            inverse = f and f[0] in ('!', '~')
-            if inverse:
-                f = f[1:]
+
+        for flag in flags:
+            negate = flag and flag[0] in ('!', '~')
+            if negate:
+                flag = flag[1:]
+
             try:
-                if inverse:
-                    self._flags &= ~FLAG_MAP[f]
+                if negate:
+                    self._flags &= ~FLAG_MAP[flag]
+
                 else:
-                    self._flags |= FLAG_MAP[f]
+                    self._flags |= FLAG_MAP[flag]
+
             except KeyError:
-                raise error.PySnmpError('bad debug flag %s' % f)
+                raise error.PySnmpError('bad debug flag %s' % flag)
 
-            self('debug category \'%s\' %s' % (f, inverse and 'disabled' or 'enabled'))
+            self('debug category "%s" '
+                 '%s' % (flag, negate and 'disabled' or 'enabled'))
 
     def __str__(self):
         return 'logger %s, flags %x' % (self._printer, self._flags)
@@ -128,5 +143,5 @@ def setLogger(l):
 
 def hexdump(octets):
     return ' '.join(
-        ['%s%.2X' % (n % 16 == 0 and ('\n%.5d: ' % n) or '', x)
-         for n, x in zip(range(len(octets)), octs2ints(octets))])
+        '%s%.2X' % (n % 16 == 0 and ('\n%.5d: ' % n) or '', x)
+        for n, x in zip(range(len(octets)), octs2ints(octets)))
diff --git a/pysnmp/entity/config.py b/pysnmp/entity/config.py
index 0ae87c0b..57e8704f 100644
--- a/pysnmp/entity/config.py
+++ b/pysnmp/entity/config.py
@@ -77,9 +77,13 @@ PRIV_SERVICES = {
 def __cookV1SystemInfo(snmpEngine, communityIndex):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
-    snmpCommunityEntry, = mibBuilder.importSymbols('SNMP-COMMUNITY-MIB', 'snmpCommunityEntry')
+    snmpEngineID, = mibBuilder.importSymbols(
+        '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+    snmpCommunityEntry, = mibBuilder.importSymbols(
+        'SNMP-COMMUNITY-MIB', 'snmpCommunityEntry')
+
     tblIdx = snmpCommunityEntry.getInstIdFromIndices(communityIndex)
+
     return snmpCommunityEntry, tblIdx, snmpEngineID
 
 
@@ -91,6 +95,7 @@ def addV1System(snmpEngine, communityIndex, communityName,
 
     if contextEngineId is None:
         contextEngineId = snmpEngineID.syntax
+
     else:
         contextEngineId = snmpEngineID.syntax.clone(contextEngineId)
 
@@ -101,10 +106,13 @@ def addV1System(snmpEngine, communityIndex, communityName,
         (snmpCommunityEntry.name + (8,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpCommunityEntry.name + (1,) + tblIdx, communityIndex),
         (snmpCommunityEntry.name + (2,) + tblIdx, communityName),
-        (snmpCommunityEntry.name + (3,) + tblIdx, securityName is not None and securityName or communityIndex),
+        (snmpCommunityEntry.name + (3,) + tblIdx, (
+                securityName is not None and securityName or
+                communityIndex)),
         (snmpCommunityEntry.name + (4,) + tblIdx, contextEngineId),
         (snmpCommunityEntry.name + (5,) + tblIdx, contextName),
         (snmpCommunityEntry.name + (6,) + tblIdx, transportTag),
@@ -117,6 +125,7 @@ def addV1System(snmpEngine, communityIndex, communityName,
 def delV1System(snmpEngine, communityIndex):
     (snmpCommunityEntry, tblIdx,
      snmpEngineID) = __cookV1SystemInfo(snmpEngine, communityIndex)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpCommunityEntry.name + (8,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
@@ -126,17 +135,23 @@ def delV1System(snmpEngine, communityIndex):
 def __cookV3UserInfo(snmpEngine, securityName, securityEngineId):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+    snmpEngineID, = mibBuilder.importSymbols(
+        '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
     if securityEngineId is None:
         snmpEngineID = snmpEngineID.syntax
+
     else:
         snmpEngineID = snmpEngineID.syntax.clone(securityEngineId)
 
-    usmUserEntry, = mibBuilder.importSymbols('SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+    usmUserEntry, = mibBuilder.importSymbols(
+        'SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+
     tblIdx1 = usmUserEntry.getInstIdFromIndices(snmpEngineID, securityName)
 
-    pysnmpUsmSecretEntry, = mibBuilder.importSymbols('PYSNMP-USM-MIB', 'pysnmpUsmSecretEntry')
+    pysnmpUsmSecretEntry, = mibBuilder.importSymbols(
+        'PYSNMP-USM-MIB', 'pysnmpUsmSecretEntry')
+
     tblIdx2 = pysnmpUsmSecretEntry.getInstIdFromIndices(securityName)
 
     return snmpEngineID, usmUserEntry, tblIdx1, pysnmpUsmSecretEntry, tblIdx2
@@ -147,24 +162,29 @@ def addV3User(snmpEngine, userName,
               privProtocol=USM_PRIV_NONE, privKey=None,
               securityEngineId=None,
               securityName=None):
+
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
     if securityName is None:
         securityName = userName
 
     (snmpEngineID, usmUserEntry, tblIdx1,
-     pysnmpUsmSecretEntry, tblIdx2) = __cookV3UserInfo(snmpEngine, userName, securityEngineId)
+     pysnmpUsmSecretEntry, tblIdx2) = __cookV3UserInfo(
+        snmpEngine, userName, securityEngineId)
 
     # Load augmenting table before creating new row in base one
-    pysnmpUsmKeyEntry, = mibBuilder.importSymbols('PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
+    pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+        'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
 
     # Load clone-from (may not be needed)
-    zeroDotZero, = mibBuilder.importSymbols('SNMPv2-SMI', 'zeroDotZero')
+    zeroDotZero, = mibBuilder.importSymbols(
+        'SNMPv2-SMI', 'zeroDotZero')
 
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (usmUserEntry.name + (13,) + tblIdx1, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (usmUserEntry.name + (2,) + tblIdx1, userName),
         (usmUserEntry.name + (3,) + tblIdx1, securityName),
@@ -180,9 +200,11 @@ def addV3User(snmpEngine, userName,
         hashedAuthPassphrase = AUTH_SERVICES[authProtocol].hashPassphrase(
             authKey and authKey or null
         )
+
         localAuthKey = AUTH_SERVICES[authProtocol].localizeKey(
             hashedAuthPassphrase, snmpEngineID
         )
+
     else:
         raise error.PySnmpError('Unknown auth protocol %s' % (authProtocol,))
 
@@ -190,9 +212,11 @@ def addV3User(snmpEngine, userName,
         hashedPrivPassphrase = PRIV_SERVICES[privProtocol].hashPassphrase(
             authProtocol, privKey and privKey or null
         )
+
         localPrivKey = PRIV_SERVICES[privProtocol].localizeKey(
             authProtocol, hashedPrivPassphrase, snmpEngineID
         )
+
     else:
         raise error.PySnmpError('Unknown priv protocol %s' % (privProtocol,))
 
@@ -211,6 +235,7 @@ def addV3User(snmpEngine, userName,
         (pysnmpUsmSecretEntry.name + (4,) + tblIdx2, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (pysnmpUsmSecretEntry.name + (1,) + tblIdx2, userName),
         (pysnmpUsmSecretEntry.name + (2,) + tblIdx2, authKey),
@@ -225,10 +250,12 @@ def delV3User(snmpEngine,
               securityEngineId=None):
     (snmpEngineID, usmUserEntry, tblIdx1, pysnmpUsmSecretEntry,
      tblIdx2) = __cookV3UserInfo(snmpEngine, userName, securityEngineId)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (usmUserEntry.name + (13,) + tblIdx1, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (pysnmpUsmSecretEntry.name + (4,) + tblIdx2, 'destroy'),
         snmpEngine=snmpEngine
@@ -272,6 +299,7 @@ def __cookTargetParamsInfo(snmpEngine, name):
 
     snmpTargetParamsEntry, = mibBuilder.importSymbols('SNMP-TARGET-MIB', 'snmpTargetParamsEntry')
     tblIdx = snmpTargetParamsEntry.getInstIdFromIndices(name)
+
     return snmpTargetParamsEntry, tblIdx
 
 
@@ -279,10 +307,13 @@ def __cookTargetParamsInfo(snmpEngine, name):
 def addTargetParams(snmpEngine, name, securityName, securityLevel, mpModel=3):
     if mpModel == 0:
         securityModel = 1
+
     elif mpModel in (1, 2):
         securityModel = 2
+
     elif mpModel == 3:
         securityModel = 3
+
     else:
         raise error.PySnmpError('Unknown MP model %s' % mpModel)
 
@@ -292,6 +323,7 @@ def addTargetParams(snmpEngine, name, securityName, securityLevel, mpModel=3):
         (snmpTargetParamsEntry.name + (7,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpTargetParamsEntry.name + (1,) + tblIdx, name),
         (snmpTargetParamsEntry.name + (2,) + tblIdx, mpModel),
@@ -323,28 +355,36 @@ def __cookTargetAddrInfo(snmpEngine, addrName):
 def addTargetAddr(snmpEngine, addrName, transportDomain, transportAddress,
                   params, timeout=None, retryCount=None, tagList=null,
                   sourceAddress=None):
+
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    (snmpTargetAddrEntry, snmpSourceAddrEntry,
+    (snmpTargetAddrEntry,
+     snmpSourceAddrEntry,
      tblIdx) = __cookTargetAddrInfo(snmpEngine, addrName)
 
     if transportDomain[:len(SNMP_UDP_DOMAIN)] == SNMP_UDP_DOMAIN:
         SnmpUDPAddress, = mibBuilder.importSymbols('SNMPv2-TM', 'SnmpUDPAddress')
         transportAddress = SnmpUDPAddress(transportAddress)
+
         if sourceAddress is None:
             sourceAddress = ('0.0.0.0', 0)
+
         sourceAddress = SnmpUDPAddress(sourceAddress)
+
     elif transportDomain[:len(SNMP_UDP6_DOMAIN)] == SNMP_UDP6_DOMAIN:
         TransportAddressIPv6, = mibBuilder.importSymbols('TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
         transportAddress = TransportAddressIPv6(transportAddress)
+
         if sourceAddress is None:
             sourceAddress = ('::', 0)
+
         sourceAddress = TransportAddressIPv6(sourceAddress)
 
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpTargetAddrEntry.name + (9,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpTargetAddrEntry.name + (1,) + tblIdx, addrName),
         (snmpTargetAddrEntry.name + (2,) + tblIdx, transportDomain),
@@ -362,6 +402,7 @@ def addTargetAddr(snmpEngine, addrName, transportDomain, transportAddress,
 def delTargetAddr(snmpEngine, addrName):
     (snmpTargetAddrEntry, snmpSourceAddrEntry,
      tblIdx) = __cookTargetAddrInfo(snmpEngine, addrName)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpTargetAddrEntry.name + (9,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
@@ -372,18 +413,23 @@ def addTransport(snmpEngine, transportDomain, transport):
     if snmpEngine.transportDispatcher:
         if not transport.isCompatibleWithDispatcher(snmpEngine.transportDispatcher):
             raise error.PySnmpError(
-                'Transport %r is not compatible with dispatcher %r' % (transport, snmpEngine.transportDispatcher))
+                'Transport %r is not compatible with dispatcher %r' % (
+                    transport, snmpEngine.transportDispatcher))
+
     else:
         snmpEngine.registerTransportDispatcher(
             transport.PROTO_TRANSPORT_DISPATCHER()
         )
+
         # here we note that we have created transportDispatcher automatically
         snmpEngine.setUserContext(automaticTransportDispatcher=0)
 
     snmpEngine.transportDispatcher.registerTransport(transportDomain, transport)
+
     automaticTransportDispatcher = snmpEngine.getUserContext(
         'automaticTransportDispatcher'
     )
+
     if automaticTransportDispatcher is not None:
         snmpEngine.setUserContext(
             automaticTransportDispatcher=automaticTransportDispatcher + 1
@@ -393,8 +439,10 @@ def addTransport(snmpEngine, transportDomain, transport):
 def getTransport(snmpEngine, transportDomain):
     if not snmpEngine.transportDispatcher:
         return
+
     try:
         return snmpEngine.transportDispatcher.getTransport(transportDomain)
+
     except error.PySnmpError:
         return
 
@@ -402,21 +450,26 @@ def getTransport(snmpEngine, transportDomain):
 def delTransport(snmpEngine, transportDomain):
     if not snmpEngine.transportDispatcher:
         return
+
     transport = getTransport(snmpEngine, transportDomain)
+
     snmpEngine.transportDispatcher.unregisterTransport(transportDomain)
+
     # automatically shutdown automatically created transportDispatcher
     automaticTransportDispatcher = snmpEngine.getUserContext(
         'automaticTransportDispatcher'
     )
+
     if automaticTransportDispatcher is not None:
         automaticTransportDispatcher -= 1
         snmpEngine.setUserContext(
-            automaticTransportDispatcher=automaticTransportDispatcher
-        )
+            automaticTransportDispatcher=automaticTransportDispatcher)
+
         if not automaticTransportDispatcher:
             snmpEngine.transportDispatcher.closeDispatcher()
             snmpEngine.unregisterTransportDispatcher()
             snmpEngine.delUserContext(automaticTransportDispatcher)
+
     return transport
 
 
@@ -428,8 +481,12 @@ delSocketTransport = delTransport
 
 def __cookVacmContextInfo(snmpEngine, contextName):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
-    vacmContextEntry, = mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
+
+    vacmContextEntry, = mibBuilder.importSymbols(
+        'SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
+
     tblIdx = vacmContextEntry.getInstIdFromIndices(contextName)
+
     return vacmContextEntry, tblIdx
 
 
@@ -440,6 +497,7 @@ def addContext(snmpEngine, contextName):
         (vacmContextEntry.name + (2,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmContextEntry.name + (1,) + tblIdx, contextName),
         (vacmContextEntry.name + (2,) + tblIdx, 'createAndGo'),
@@ -459,20 +517,24 @@ def delContext(snmpEngine, contextName):
 def __cookVacmGroupInfo(snmpEngine, securityModel, securityName):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    vacmSecurityToGroupEntry, = mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB',
-                                                         'vacmSecurityToGroupEntry')
-    tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(securityModel,
-                                                           securityName)
+    vacmSecurityToGroupEntry, = mibBuilder.importSymbols(
+        'SNMP-VIEW-BASED-ACM-MIB', 'vacmSecurityToGroupEntry')
+
+    tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(
+        securityModel, securityName)
+
     return vacmSecurityToGroupEntry, tblIdx
 
 
 def addVacmGroup(snmpEngine, groupName, securityModel, securityName):
     (vacmSecurityToGroupEntry,
      tblIdx) = __cookVacmGroupInfo(snmpEngine, securityModel, securityName)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmSecurityToGroupEntry.name + (5,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmSecurityToGroupEntry.name + (1,) + tblIdx, securityModel),
         (vacmSecurityToGroupEntry.name + (2,) + tblIdx, securityName),
@@ -486,6 +548,7 @@ def delVacmGroup(snmpEngine, securityModel, securityName):
     vacmSecurityToGroupEntry, tblIdx = __cookVacmGroupInfo(
         snmpEngine, securityModel, securityName
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmSecurityToGroupEntry.name + (5,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
@@ -496,17 +559,19 @@ def __cookVacmAccessInfo(snmpEngine, groupName, contextName, securityModel,
                          securityLevel):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    vacmAccessEntry, = mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry')
-    tblIdx = vacmAccessEntry.getInstIdFromIndices(groupName, contextName,
-                                                  securityModel, securityLevel)
+    vacmAccessEntry, = mibBuilder.importSymbols(
+        'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry')
+
+    tblIdx = vacmAccessEntry.getInstIdFromIndices(
+        groupName, contextName, securityModel, securityLevel)
+
     return vacmAccessEntry, tblIdx
 
 
 def addVacmAccess(snmpEngine, groupName, contextName, securityModel,
                   securityLevel, prefix, readView, writeView, notifyView):
-    vacmAccessEntry, tblIdx = __cookVacmAccessInfo(snmpEngine, groupName,
-                                                   contextName, securityModel,
-                                                   securityLevel)
+    vacmAccessEntry, tblIdx = __cookVacmAccessInfo(
+        snmpEngine, groupName, contextName, securityModel, securityLevel)
 
     addContext(snmpEngine, contextName)
 
@@ -514,6 +579,7 @@ def addVacmAccess(snmpEngine, groupName, contextName, securityModel,
         (vacmAccessEntry.name + (9,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmAccessEntry.name + (1,) + tblIdx, contextName),
         (vacmAccessEntry.name + (2,) + tblIdx, securityModel),
@@ -529,9 +595,9 @@ def addVacmAccess(snmpEngine, groupName, contextName, securityModel,
 
 def delVacmAccess(snmpEngine, groupName, contextName, securityModel,
                   securityLevel):
-    vacmAccessEntry, tblIdx = __cookVacmAccessInfo(snmpEngine, groupName,
-                                                   contextName, securityModel,
-                                                   securityLevel)
+
+    vacmAccessEntry, tblIdx = __cookVacmAccessInfo(
+        snmpEngine, groupName, contextName, securityModel, securityLevel)
 
     delContext(snmpEngine, contextName)
 
@@ -545,19 +611,23 @@ def __cookVacmViewInfo(snmpEngine, viewName, subTree):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
     vacmViewTreeFamilyEntry, = mibBuilder.importSymbols(
-        'SNMP-VIEW-BASED-ACM-MIB', 'vacmViewTreeFamilyEntry'
-    )
+        'SNMP-VIEW-BASED-ACM-MIB', 'vacmViewTreeFamilyEntry')
+
     tblIdx = vacmViewTreeFamilyEntry.getInstIdFromIndices(viewName, subTree)
+
     return vacmViewTreeFamilyEntry, tblIdx
 
 
 def addVacmView(snmpEngine, viewName, viewType, subTree, mask):
-    vacmViewTreeFamilyEntry, tblIdx = __cookVacmViewInfo(snmpEngine, viewName,
-                                                         subTree)
+
+    vacmViewTreeFamilyEntry, tblIdx = __cookVacmViewInfo(
+        snmpEngine, viewName, subTree)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmViewTreeFamilyEntry.name + (6,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmViewTreeFamilyEntry.name + (1,) + tblIdx, viewName),
         (vacmViewTreeFamilyEntry.name + (2,) + tblIdx, subTree),
@@ -569,8 +639,9 @@ def addVacmView(snmpEngine, viewName, viewType, subTree, mask):
 
 
 def delVacmView(snmpEngine, viewName, subTree):
-    vacmViewTreeFamilyEntry, tblIdx = __cookVacmViewInfo(snmpEngine, viewName,
-                                                         subTree)
+    vacmViewTreeFamilyEntry, tblIdx = __cookVacmViewInfo(
+        snmpEngine, viewName, subTree)
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (vacmViewTreeFamilyEntry.name + (6,) + tblIdx, 'destroy'),
         snmpEngine=snmpEngine
@@ -583,8 +654,11 @@ def __cookVacmUserInfo(snmpEngine, securityModel, securityName, securityLevel):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
     groupName = 'v-%s-%d' % (hash(securityName), securityModel)
+
     SnmpSecurityLevel, = mibBuilder.importSymbols('SNMP-FRAMEWORK-MIB', 'SnmpSecurityLevel')
+
     securityLevel = SnmpSecurityLevel(securityLevel)
+
     return (groupName, securityLevel,
             'r' + groupName, 'w' + groupName, 'n' + groupName)
 
@@ -592,16 +666,22 @@ def __cookVacmUserInfo(snmpEngine, securityModel, securityName, securityLevel):
 def addVacmUser(snmpEngine, securityModel, securityName, securityLevel,
                 readSubTree=(), writeSubTree=(), notifySubTree=(),
                 contextName=null):
+
     (groupName, securityLevel, readView, writeView,
-     notifyView) = __cookVacmUserInfo(snmpEngine, securityModel, securityName,
-                                      securityLevel)
+     notifyView) = __cookVacmUserInfo(
+        snmpEngine, securityModel, securityName, securityLevel)
+
     addVacmGroup(snmpEngine, groupName, securityModel, securityName)
+
     addVacmAccess(snmpEngine, groupName, contextName, securityModel,
                   securityLevel, 1, readView, writeView, notifyView)
+
     if readSubTree:
         addVacmView(snmpEngine, readView, "included", readSubTree, null)
+
     if writeSubTree:
         addVacmView(snmpEngine, writeView, "included", writeSubTree, null)
+
     if notifySubTree:
         addVacmView(snmpEngine, notifyView, "included", notifySubTree, null)
 
@@ -610,43 +690,48 @@ def delVacmUser(snmpEngine, securityModel, securityName, securityLevel,
                 readSubTree=(), writeSubTree=(), notifySubTree=(),
                 contextName=null):
     (groupName, securityLevel, readView, writeView,
-     notifyView) = __cookVacmUserInfo(snmpEngine, securityModel,
-                                      securityName, securityLevel)
+     notifyView) = __cookVacmUserInfo(
+        snmpEngine, securityModel, securityName, securityLevel)
+
     delVacmGroup(snmpEngine, securityModel, securityName)
+
     delVacmAccess(snmpEngine, groupName, contextName, securityModel, securityLevel)
+
     if readSubTree:
-        delVacmView(
-            snmpEngine, readView, readSubTree
-        )
+        delVacmView(snmpEngine, readView, readSubTree)
+
     if writeSubTree:
-        delVacmView(
-            snmpEngine, writeView, writeSubTree
-        )
+        delVacmView(snmpEngine, writeView, writeSubTree)
+
     if notifySubTree:
-        delVacmView(
-            snmpEngine, notifyView, notifySubTree
-        )
+        delVacmView(snmpEngine, notifyView, notifySubTree)
 
 # Notification target setup
 
 def __cookNotificationTargetInfo(snmpEngine, notificationName, paramsName,
                                  filterSubtree=None):
+
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    snmpNotifyEntry, = mibBuilder.importSymbols('SNMP-NOTIFICATION-MIB', 'snmpNotifyEntry')
+    snmpNotifyEntry, = mibBuilder.importSymbols(
+        'SNMP-NOTIFICATION-MIB', 'snmpNotifyEntry')
+
     tblIdx1 = snmpNotifyEntry.getInstIdFromIndices(notificationName)
 
-    snmpNotifyFilterProfileEntry, = mibBuilder.importSymbols('SNMP-NOTIFICATION-MIB',
-                                                             'snmpNotifyFilterProfileEntry')
+    snmpNotifyFilterProfileEntry, = mibBuilder.importSymbols(
+        'SNMP-NOTIFICATION-MIB', 'snmpNotifyFilterProfileEntry')
+
     tblIdx2 = snmpNotifyFilterProfileEntry.getInstIdFromIndices(paramsName)
 
     profileName = '%s-filter' % hash(notificationName)
 
     if filterSubtree:
-        snmpNotifyFilterEntry, = mibBuilder.importSymbols('SNMP-NOTIFICATION-MIB',
-                                                          'snmpNotifyFilterEntry')
-        tblIdx3 = snmpNotifyFilterEntry.getInstIdFromIndices(profileName,
-                                                             filterSubtree)
+        snmpNotifyFilterEntry, = mibBuilder.importSymbols(
+            'SNMP-NOTIFICATION-MIB', 'snmpNotifyFilterEntry')
+
+        tblIdx3 = snmpNotifyFilterEntry.getInstIdFromIndices(
+            profileName, filterSubtree)
+
     else:
         snmpNotifyFilterEntry = tblIdx3 = None
 
@@ -658,15 +743,17 @@ def __cookNotificationTargetInfo(snmpEngine, notificationName, paramsName,
 def addNotificationTarget(snmpEngine, notificationName, paramsName,
                           transportTag, notifyType=None, filterSubtree=None,
                           filterMask=None, filterType=None):
+
     (snmpNotifyEntry, tblIdx1, snmpNotifyFilterProfileEntry, tblIdx2,
      profileName, snmpNotifyFilterEntry,
-     tblIdx3) = __cookNotificationTargetInfo(snmpEngine, notificationName,
-                                             paramsName, filterSubtree)
+     tblIdx3) = __cookNotificationTargetInfo(
+        snmpEngine, notificationName, paramsName, filterSubtree)
 
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpNotifyEntry.name + (5,) + tblIdx1, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpNotifyEntry.name + (2,) + tblIdx1, transportTag),
         (snmpNotifyEntry.name + (3,) + tblIdx1, notifyType),
@@ -678,6 +765,7 @@ def addNotificationTarget(snmpEngine, notificationName, paramsName,
         (snmpNotifyFilterProfileEntry.name + (3,) + tblIdx2, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpNotifyFilterProfileEntry.name + (1,) + tblIdx2, profileName),
         (snmpNotifyFilterProfileEntry.name + (3,) + tblIdx2, 'createAndGo'),
@@ -691,6 +779,7 @@ def addNotificationTarget(snmpEngine, notificationName, paramsName,
         (snmpNotifyFilterEntry.name + (5,) + tblIdx3, 'destroy'),
         snmpEngine=snmpEngine
     )
+
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpNotifyFilterEntry.name + (1,) + tblIdx3, filterSubtree),
         (snmpNotifyFilterEntry.name + (2,) + tblIdx3, filterMask),
@@ -704,8 +793,8 @@ def delNotificationTarget(snmpEngine, notificationName, paramsName,
                           filterSubtree=None):
     (snmpNotifyEntry, tblIdx1, snmpNotifyFilterProfileEntry,
      tblIdx2, profileName, snmpNotifyFilterEntry,
-     tblIdx3) = __cookNotificationTargetInfo(snmpEngine, notificationName,
-                                             paramsName, filterSubtree)
+     tblIdx3) = __cookNotificationTargetInfo(
+        snmpEngine, notificationName, paramsName, filterSubtree)
 
     snmpEngine.msgAndPduDsp.mibInstrumController.writeMibObjects(
         (snmpNotifyEntry.name + (5,) + tblIdx1, 'destroy'),
diff --git a/pysnmp/entity/engine.py b/pysnmp/entity/engine.py
index 60b45b0c..d7f16ff8 100644
--- a/pysnmp/entity/engine.py
+++ b/pysnmp/entity/engine.py
@@ -65,8 +65,12 @@ class SnmpEngine(object):
 
         if msgAndPduDsp is None:
             self.msgAndPduDsp = MsgAndPduDispatcher()
+
         else:
             self.msgAndPduDsp = msgAndPduDsp
+
+        mibBuilder = self.msgAndPduDsp.mibInstrumController.mibBuilder
+
         self.messageProcessingSubsystems = {
             SnmpV1MessageProcessingModel.MESSAGE_PROCESSING_MODEL_ID:
                 SnmpV1MessageProcessingModel(),
@@ -75,11 +79,13 @@ class SnmpEngine(object):
             SnmpV3MessageProcessingModel.MESSAGE_PROCESSING_MODEL_ID:
                 SnmpV3MessageProcessingModel()
         }
+
         self.securityModels = {
             SnmpV1SecurityModel.SECURITY_MODEL_ID: SnmpV1SecurityModel(),
             SnmpV2cSecurityModel.SECURITY_MODEL_ID: SnmpV2cSecurityModel(),
             SnmpUSMSecurityModel.SECURITY_MODEL_ID: SnmpUSMSecurityModel()
         }
+
         self.accessControlModel = {
             void.Vacm.ACCESS_MODEL_ID: void.Vacm(),
             rfc3415.Vacm.ACCESS_MODEL_ID: rfc3415.Vacm()
@@ -88,48 +94,59 @@ class SnmpEngine(object):
         self.transportDispatcher = None
 
         if self.msgAndPduDsp.mibInstrumController is None:
-            raise error.PySnmpError(
-                'MIB instrumentation does not yet exist'
-            )
-        snmpEngineMaxMessageSize, = self.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+            raise error.PySnmpError('MIB instrumentation does not yet exist')
+
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
             '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+
         snmpEngineMaxMessageSize.syntax = snmpEngineMaxMessageSize.syntax.clone(maxMessageSize)
-        snmpEngineBoots, = self.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                           'snmpEngineBoots')
+
+        snmpEngineBoots, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots')
+
         snmpEngineBoots.syntax += 1
-        origSnmpEngineID, = self.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                            'snmpEngineID')
+
+        origSnmpEngineID, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
         if snmpEngineID is None:
             self.snmpEngineID = origSnmpEngineID.syntax
+
         else:
             origSnmpEngineID.syntax = origSnmpEngineID.syntax.clone(snmpEngineID)
             self.snmpEngineID = origSnmpEngineID.syntax
 
             debug.logger & debug.FLAG_APP and debug.logger(
-                'SnmpEngine: using custom SNMP Engine ID: %s' % self.snmpEngineID.prettyPrint())
+                'SnmpEngine: using custom SNMP Engine '
+                'ID: %s' % self.snmpEngineID.prettyPrint())
 
             # Attempt to make some of snmp Engine settings persistent.
             # This should probably be generalized as a non-volatile MIB store.
 
-            persistentPath = os.path.join(tempfile.gettempdir(), '__pysnmp', self.snmpEngineID.prettyPrint())
+            persistentPath = os.path.join(tempfile.gettempdir(), '__pysnmp',
+                                          self.snmpEngineID.prettyPrint())
 
-            debug.logger & debug.FLAG_APP and debug.logger('SnmpEngine: using persistent directory: %s' % persistentPath)
+            debug.logger & debug.FLAG_APP and debug.logger(
+                'SnmpEngine: using persistent directory: %s' % persistentPath)
 
             if not os.path.exists(persistentPath):
                 try:
                     os.makedirs(persistentPath)
+
                 except OSError:
                     return
 
             f = os.path.join(persistentPath, 'boots')
+
             try:
                 snmpEngineBoots.syntax = snmpEngineBoots.syntax.clone(open(f).read())
+
             except Exception:
                 pass
 
             try:
                 snmpEngineBoots.syntax += 1
+
             except Exception:
                 snmpEngineBoots.syntax = snmpEngineBoots.syntax.clone(1)
 
@@ -138,12 +155,15 @@ class SnmpEngine(object):
                 os.write(fd, str2octs(snmpEngineBoots.syntax.prettyPrint()))
                 os.close(fd)
                 shutil.move(fn, f)
+
             except Exception as exc:
                 debug.logger & debug.FLAG_APP and debug.logger(
                     'SnmpEngine: could not stored SNMP Engine Boots: %s' % exc)
+
             else:
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'SnmpEngine: stored SNMP Engine Boots: %s' % snmpEngineBoots.syntax.prettyPrint())
+                    'SnmpEngine: stored SNMP Engine Boots: '
+                    '%s' % snmpEngineBoots.syntax.prettyPrint())
 
     def __repr__(self):
         return '%s(snmpEngineID=%r)' % (self.__class__.__name__, self.snmpEngineID)
@@ -158,31 +178,28 @@ class SnmpEngine(object):
 
     def __receiveTimerTickCbFun(self, timeNow):
         self.msgAndPduDsp.receiveTimerTick(self, timeNow)
+
         for mpHandler in self.messageProcessingSubsystems.values():
             mpHandler.receiveTimerTick(self, timeNow)
+
         for smHandler in self.securityModels.values():
             smHandler.receiveTimerTick(self, timeNow)
 
     def registerTransportDispatcher(self, transportDispatcher, recvId=None):
-        if self.transportDispatcher is not None and \
-                self.transportDispatcher is not transportDispatcher:
-            raise error.PySnmpError(
-                'Transport dispatcher already registered'
-            )
-        transportDispatcher.registerRecvCbFun(
-            self.__receiveMessageCbFun, recvId
-        )
-        if self.transportDispatcher is None:
-            transportDispatcher.registerTimerCbFun(
-                self.__receiveTimerTickCbFun
-            )
+        if (self.transportDispatcher and
+                self.transportDispatcher is not transportDispatcher):
+            raise error.PySnmpError('Transport dispatcher already registered')
+
+        transportDispatcher.registerRecvCbFun(self.__receiveMessageCbFun, recvId)
+
+        if not self.transportDispatcher:
+            transportDispatcher.registerTimerCbFun(self.__receiveTimerTickCbFun)
             self.transportDispatcher = transportDispatcher
 
     def unregisterTransportDispatcher(self, recvId=None):
         if self.transportDispatcher is None:
-            raise error.PySnmpError(
-                'Transport dispatcher not registered'
-            )
+            raise error.PySnmpError('Transport dispatcher not registered')
+
         self.transportDispatcher.unregisterRecvCbFun(recvId)
         self.transportDispatcher.unregisterTimerCbFun()
         self.transportDispatcher = None
@@ -192,9 +209,7 @@ class SnmpEngine(object):
 
     # User app may attach opaque objects to SNMP Engine
     def setUserContext(self, **kwargs):
-        self.cache.update(
-            dict([('__%s' % k, kwargs[k]) for k in kwargs])
-        )
+        self.cache.update(dict([('__%s' % k, kwargs[k]) for k in kwargs]))
 
     def getUserContext(self, arg):
         return self.cache.get('__%s' % arg)
@@ -202,5 +217,6 @@ class SnmpEngine(object):
     def delUserContext(self, arg):
         try:
             del self.cache['__%s' % arg]
+
         except KeyError:
             pass
diff --git a/pysnmp/entity/observer.py b/pysnmp/entity/observer.py
index 3f7bd845..ddc959c3 100644
--- a/pysnmp/entity/observer.py
+++ b/pysnmp/entity/observer.py
@@ -31,21 +31,26 @@ class MetaObserver(object):
     def registerObserver(self, cbFun, *execpoints, **kwargs):
         if cbFun in self.__contexts:
             raise error.PySnmpError('duplicate observer %s' % cbFun)
+
         else:
             self.__contexts[cbFun] = kwargs.get('cbCtx')
+
         for execpoint in execpoints:
             if execpoint not in self.__observers:
                 self.__observers[execpoint] = []
+
             self.__observers[execpoint].append(cbFun)
 
     def unregisterObserver(self, cbFun=None):
         if cbFun is None:
             self.__observers.clear()
             self.__contexts.clear()
+
         else:
             for execpoint in dict(self.__observers):
                 if cbFun in self.__observers[execpoint]:
                     self.__observers[execpoint].remove(cbFun)
+
                 if not self.__observers[execpoint]:
                     del self.__observers[execpoint]
 
@@ -59,6 +64,7 @@ class MetaObserver(object):
         if execpoints:
             for execpoint in execpoints:
                 del self.__execpoints[execpoint]
+
         else:
             self.__execpoints.clear()
 
diff --git a/pysnmp/entity/rfc3413/cmdgen.py b/pysnmp/entity/rfc3413/cmdgen.py
index 6f13c265..17db6f33 100644
--- a/pysnmp/entity/rfc3413/cmdgen.py
+++ b/pysnmp/entity/rfc3413/cmdgen.py
@@ -49,7 +49,8 @@ class CommandGenerator(object):
         # 3.1.3
         if statusInformation:
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponsePdu: sendPduHandle %s, statusInformation %s' % (sendPduHandle, statusInformation))
+                'processResponsePdu: sendPduHandle %s, statusInformation '
+                '%s' % (sendPduHandle, statusInformation))
 
             errorIndication = statusInformation['errorIndication']
 
@@ -60,16 +61,22 @@ class CommandGenerator(object):
                 origDiscoveryRetries = 0
                 origRetries += 1
 
-            if origRetries > origRetryCount or origDiscoveryRetries > self.__options.get('discoveryRetries', 4):
+            if (origRetries > origRetryCount or
+                    origDiscoveryRetries > self.__options.get('discoveryRetries', 4)):
+
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'processResponsePdu: sendPduHandle %s, retry count %d exceeded' % (sendPduHandle, origRetries))
-                cbFun(snmpEngine, origSendRequestHandle, errorIndication, None, cbCtx)
+                    'processResponsePdu: sendPduHandle %s, retry count %d '
+                    'exceeded' % (sendPduHandle, origRetries))
+
+                cbFun(snmpEngine, origSendRequestHandle,
+                      errorIndication, None, cbCtx)
                 return
 
             # User-side API assumes SMIv2
             if origMessageProcessingModel == 0:
                 reqPDU = rfc2576.v2ToV1(origPdu)
                 pduVersion = 0
+
             else:
                 reqPDU = origPdu
                 pduVersion = 1
@@ -92,16 +99,20 @@ class CommandGenerator(object):
                     origContextName, origPduVersion, origPdu, origTimeout,
                     origRetryCount, origRetries, origDiscoveryRetries
                 )
+
                 return
 
             except StatusInformation as exc:
                 statusInformation = exc
+
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'processResponsePdu: origSendRequestHandle %s, _sendPdu() failed with %r' % (
-                    sendPduHandle, statusInformation))
+                    'processResponsePdu: origSendRequestHandle %s, _sendPdu() '
+                    'failed with %r' % (sendPduHandle, statusInformation))
+
                 cbFun(snmpEngine, origSendRequestHandle,
                       statusInformation['errorIndication'],
                       None, cbCtx)
+
                 return
 
         if (origMessageProcessingModel != messageProcessingModel or
@@ -110,11 +121,14 @@ class CommandGenerator(object):
                 origContextEngineId and origContextEngineId != contextEngineId or
                 origContextName and origContextName != contextName or
                 origPduVersion != pduVersion):
+
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponsePdu: sendPduHandle %s, request/response data mismatch' % sendPduHandle)
+                'processResponsePdu: sendPduHandle %s, request/response '
+                'data mismatch' % sendPduHandle)
 
             cbFun(snmpEngine, origSendRequestHandle,
                   'badResponse', None, cbCtx)
+
             return
 
         # User-side API assumes SMIv2
@@ -124,9 +138,12 @@ class CommandGenerator(object):
         # 3.1.2
         if v2c.apiPDU.getRequestID(PDU) != v2c.apiPDU.getRequestID(origPdu):
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponsePdu: sendPduHandle %s, request-id/response-id mismatch' % sendPduHandle)
+                'processResponsePdu: sendPduHandle %s, request-id/response-id '
+                'mismatch' % sendPduHandle)
+
             cbFun(snmpEngine, origSendRequestHandle,
                   'badResponse', None, cbCtx)
+
             return
 
         cbFun(snmpEngine, origSendRequestHandle, None, PDU, cbCtx)
@@ -139,14 +156,18 @@ class CommandGenerator(object):
          securityLevel) = config.getTargetInfo(snmpEngine, targetName)
 
         # Convert timeout in seconds into timeout in timer ticks
-        timeoutInTicks = float(timeout) / 100 / snmpEngine.transportDispatcher.getTimerResolution()
+        timeoutInTicks = (float(timeout) / 100 /
+                          snmpEngine.transportDispatcher.getTimerResolution())
+
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-        SnmpEngineID, SnmpAdminString = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        SnmpEngineID, SnmpAdminString = mibBuilder.importSymbols(
             'SNMP-FRAMEWORK-MIB', 'SnmpEngineID', 'SnmpAdminString')
 
         # Cast possible strings into bytes
         if contextEngineId:
             contextEngineId = SnmpEngineID(contextEngineId)
+
         contextName = SnmpAdminString(contextName)
 
         origPDU = PDU
@@ -155,6 +176,7 @@ class CommandGenerator(object):
         if messageProcessingModel == 0:
             PDU = rfc2576.v2ToV1(PDU)
             pduVersion = 0
+
         else:
             pduVersion = 1
 
@@ -179,13 +201,14 @@ class CommandGenerator(object):
         )
 
         debug.logger & debug.FLAG_APP and debug.logger(
-            'sendPdu: sendPduHandle %s, timeout %d*10 ms/%d ticks, retry 0 of %d' % (
-                sendPduHandle, timeout, timeoutInTicks, retryCount))
+            'sendPdu: sendPduHandle %s, timeout %d*10 ms/%d ticks, retry '
+            '0 of %d' % (sendPduHandle, timeout, timeoutInTicks, retryCount))
 
         return sendRequestHandle
 
 
 class GetCommandGenerator(CommandGenerator):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         cbFun, cbCtx = cbCtx
@@ -208,6 +231,7 @@ class GetCommandGenerator(CommandGenerator):
 
 
 class SetCommandGenerator(CommandGenerator):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         cbFun, cbCtx = cbCtx
@@ -225,11 +249,12 @@ class SetCommandGenerator(CommandGenerator):
         v2c.apiPDU.setVarBinds(reqPDU, varBinds)
 
         return self.sendPdu(snmpEngine, targetName, contextEngineId,
-                            contextName, reqPDU,
-                            self.processResponseVarBinds, (cbFun, cbCtx))
+                            contextName, reqPDU, self.processResponseVarBinds,
+                            (cbFun, cbCtx))
 
 
 class NextCommandGeneratorSingleRun(CommandGenerator):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         targetName, contextEngineId, contextName, reqPDU, cbFun, cbCtx = cbCtx
@@ -253,6 +278,7 @@ class NextCommandGeneratorSingleRun(CommandGenerator):
 
 
 class NextCommandGenerator(NextCommandGeneratorSingleRun):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         targetName, contextEngineId, contextName, reqPDU, cbFun, cbCtx = cbCtx
@@ -266,8 +292,10 @@ class NextCommandGenerator(NextCommandGeneratorSingleRun):
 
         if v2c.apiPDU.getErrorStatus(PDU):
             errorIndication, varBinds = None, ()
+
         elif not varBindTable:
             errorIndication, varBinds = errind.emptyResponse, ()
+
         else:
             errorIndication, varBinds = v2c.apiPDU.getNextVarBinds(varBindTable[-1])
 
@@ -275,9 +303,11 @@ class NextCommandGenerator(NextCommandGeneratorSingleRun):
                      v2c.apiPDU.getErrorStatus(PDU),
                      v2c.apiPDU.getErrorIndex(PDU, muteErrors=True),
                      varBindTable, cbCtx):
+
             debug.logger & debug.FLAG_APP and debug.logger(
                 'processResponseVarBinds: sendRequestHandle %s, app says to stop walking' % sendRequestHandle)
-            return  # app says enough
+
+            return  # app says it's enough
 
         if not varBinds:
             return  # no more objects available
@@ -294,14 +324,18 @@ class NextCommandGenerator(NextCommandGeneratorSingleRun):
 
         except StatusInformation as exc:
             statusInformation = exc
+
             debug.logger & debug.FLAG_APP and debug.logger(
-                'sendVarBinds: sendPduHandle %s: sendPdu() failed with %r' % (sendRequestHandle, statusInformation))
+                'sendVarBinds: sendPduHandle %s: sendPdu() failed with '
+                '%r' % (sendRequestHandle, statusInformation))
+
             cbFun(snmpEngine, sendRequestHandle,
                   statusInformation['errorIndication'],
                   0, 0, (), cbCtx)
 
 
 class BulkCommandGeneratorSingleRun(CommandGenerator):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         (targetName, nonRepeaters, maxRepetitions,
@@ -332,6 +366,7 @@ class BulkCommandGeneratorSingleRun(CommandGenerator):
 
 
 class BulkCommandGenerator(BulkCommandGeneratorSingleRun):
+
     def processResponseVarBinds(self, snmpEngine, sendRequestHandle,
                                 errorIndication, PDU, cbCtx):
         (targetName, nonRepeaters, maxRepetitions,
@@ -346,21 +381,27 @@ class BulkCommandGenerator(BulkCommandGeneratorSingleRun):
 
         if v2c.apiBulkPDU.getErrorStatus(PDU):
             errorIndication, varBinds = None, ()
+
         elif not varBindTable:
             errorIndication, varBinds = errind.emptyResponse, ()
+
         else:
             errorIndication, varBinds = v2c.apiBulkPDU.getNextVarBinds(varBindTable[-1])
             nonRepeaters = v2c.apiBulkPDU.getNonRepeaters(reqPDU)
+
             if nonRepeaters:
                 varBinds = v2c.apiBulkPDU.getVarBinds(reqPDU)[:int(nonRepeaters)] + varBinds[int(nonRepeaters):]
 
-        if not cbFun(snmpEngine, sendRequestHandle, errorIndication,
-                     v2c.apiBulkPDU.getErrorStatus(PDU),
-                     v2c.apiBulkPDU.getErrorIndex(PDU, muteErrors=True),
-                     varBindTable, cbCtx):
+        if not cbFun(
+                snmpEngine, sendRequestHandle, errorIndication,
+                v2c.apiBulkPDU.getErrorStatus(PDU),
+                v2c.apiBulkPDU.getErrorIndex(PDU, muteErrors=True),
+                varBindTable, cbCtx):
+
             debug.logger & debug.FLAG_APP and debug.logger(
                 'processResponseVarBinds: sendRequestHandle %s, app says to stop walking' % sendRequestHandle)
-            return  # app says enough
+
+            return  # app says it's enough
 
         if not varBinds:
             return  # no more objects available
@@ -369,16 +410,18 @@ class BulkCommandGenerator(BulkCommandGeneratorSingleRun):
         v2c.apiBulkPDU.setVarBinds(reqPDU, varBinds)
 
         try:
-            self.sendPdu(snmpEngine, targetName, contextEngineId,
-                         contextName, reqPDU,
-                         self.processResponseVarBinds,
-                         (targetName, nonRepeaters, maxRepetitions,
-                          contextEngineId, contextName, reqPDU, cbFun, cbCtx))
+            self.sendPdu(
+                snmpEngine, targetName, contextEngineId, contextName, reqPDU,
+                self.processResponseVarBinds,
+                (targetName, nonRepeaters, maxRepetitions,
+                    contextEngineId, contextName, reqPDU, cbFun, cbCtx))
 
         except StatusInformation as exc:
             statusInformation = exc
+
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponseVarBinds: sendPduHandle %s: _sendPdu() failed with %r' % (
-                    sendRequestHandle, statusInformation))
+                'processResponseVarBinds: sendPduHandle %s: _sendPdu() failed '
+                'with %r' % (sendRequestHandle, statusInformation))
+
             cbFun(snmpEngine, sendRequestHandle,
                   statusInformation['errorIndication'], 0, 0, (), cbCtx)
diff --git a/pysnmp/entity/rfc3413/cmdrsp.py b/pysnmp/entity/rfc3413/cmdrsp.py
index 7910b86b..56eaaaf3 100644
--- a/pysnmp/entity/rfc3413/cmdrsp.py
+++ b/pysnmp/entity/rfc3413/cmdrsp.py
@@ -79,9 +79,8 @@ class CommandResponderBase(object):
         v2c.apiPDU.setVarBinds(PDU, varBinds)
 
         debug.logger & debug.FLAG_APP and debug.logger(
-            'sendVarBinds: stateReference %s, errorStatus %s, errorIndex %s, varBinds %s' % (
-            stateReference, errorStatus, errorIndex, varBinds)
-        )
+            'sendVarBinds: stateReference %s, errorStatus %s, errorIndex %s, '
+            'varBinds %s' % (stateReference, errorStatus, errorIndex, varBinds))
 
         self.sendPdu(snmpEngine, stateReference, PDU)
 
@@ -121,9 +120,12 @@ class CommandResponderBase(object):
 
         except error.StatusInformation as exc:
             debug.logger & debug.FLAG_APP and debug.logger(
-                'sendPdu: stateReference %s, statusInformation %s' % (stateReference, exc))
-            snmpSilentDrops, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB',
-                                                                                                     'snmpSilentDrops')
+                'sendPdu: stateReference %s, statusInformation '
+                '%s' % (stateReference, exc))
+
+            snmpSilentDrops, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpSilentDrops')
+
             snmpSilentDrops.syntax += 1
 
     _getRequestType = rfc1905.GetRequestPDU.tagSet
@@ -172,6 +174,7 @@ class CommandResponderBase(object):
     def _storeAccessContext(snmpEngine):
         """Copy received message metadata while it lasts"""
         execCtx = snmpEngine.observer.getExecutionContext('rfc3412.receiveMessage:request')
+
         return {
             'securityModel': execCtx['securityModel'],
             'securityName': execCtx['securityName'],
@@ -205,14 +208,19 @@ class CommandResponderBase(object):
         # Map ACM errors onto SMI ones
         except error.StatusInformation as exc:
             statusInformation = exc
+
             debug.logger & debug.FLAG_APP and debug.logger(
-                '__verifyAccess: name %s, statusInformation %s' % (name, statusInformation))
+                '__verifyAccess: name %s, statusInformation '
+                '%s' % (name, statusInformation))
+
             errorIndication = statusInformation['errorIndication']
+
             # 3.2.5...
             if (errorIndication == errind.noSuchView or
                     errorIndication == errind.noAccessEntry or
                     errorIndication == errind.noGroupName):
-                raise pysnmp.smi.error.AuthorizationError(name=name, idx=context.get('idx'))
+                raise pysnmp.smi.error.AuthorizationError(
+                    name=name, idx=context.get('idx'))
 
             elif errorIndication == errind.otherError:
                 raise pysnmp.smi.error.GenError(name=name, idx=context.get('idx'))
@@ -221,16 +229,18 @@ class CommandResponderBase(object):
                 snmpUnknownContexts, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
                     '__SNMP-TARGET-MIB', 'snmpUnknownContexts')
                 snmpUnknownContexts.syntax += 1
+
                 # Request REPORT generation
-                raise pysnmp.smi.error.GenError(name=name, idx=context.get('idx'),
-                                                oid=snmpUnknownContexts.name,
-                                                val=snmpUnknownContexts.syntax)
+                raise pysnmp.smi.error.GenError(
+                    name=name, idx=context.get('idx'), oid=snmpUnknownContexts.name,
+                    val=snmpUnknownContexts.syntax)
 
             elif errorIndication == errind.notInView:
                 return True
 
             else:
                 raise error.ProtocolError('Unknown ACM error %s' % errorIndication)
+
         else:
             # rfc2576: 4.1.2.1
             if (securityModel == 1 and val is not None and
@@ -273,7 +283,6 @@ class CommandResponderBase(object):
         return errorIndication, errorStatus, errorIndex, varBinds
 
     def completeMgmtOperation(self, varBinds, **context):
-
         (errorIndication,
          errorStatus, errorIndex,
          varBinds) = self._mapSmiErrors(varBinds, **context)
@@ -330,11 +339,6 @@ class NextCommandResponder(CommandResponderBase):
     def _getManagedObjectsInstances(self, varBinds, **context):
         """Iterate over Managed Objects fulfilling SNMP query.
 
-        Parameters
-        ----------
-        varBinds
-        context
-
         Returns
         -------
         :py:class:`list` - List of Managed Objects Instances to respond with or
@@ -396,7 +400,7 @@ class NextCommandResponder(CommandResponderBase):
 
 class BulkCommandResponder(NextCommandResponder):
     SUPPORTED_PDU_TYPES = (rfc1905.GetBulkRequestPDU.tagSet,)
-    maxVarBinds = 64
+    MAX_VAR_BINDS = 64
 
     def _completeNonRepeaters(self, varBinds, **context):
         mgmtFun = context['mgmtFun']
@@ -470,7 +474,7 @@ class BulkCommandResponder(NextCommandResponder):
         R = max(len(varBinds) - N, 0)
 
         if R:
-            M = min(M, self.maxVarBinds // R)
+            M = min(M, self.MAX_VAR_BINDS // R)
 
         debug.logger & debug.FLAG_APP and debug.logger(
             'initiateMgmtOperation: N %d, M %d, R %d' % (N, M, R))
diff --git a/pysnmp/entity/rfc3413/config.py b/pysnmp/entity/rfc3413/config.py
index c58c74ba..162b70a0 100644
--- a/pysnmp/entity/rfc3413/config.py
+++ b/pysnmp/entity/rfc3413/config.py
@@ -36,7 +36,8 @@ def getTargetAddr(snmpEngine, snmpTargetAddrName):
             'snmpTargetAddrTAddress', 'snmpTargetAddrTimeout',
             'snmpTargetAddrRetryCount', 'snmpTargetAddrParams'
         )
-        snmpSourceAddrTAddress, = mibBuilder.importSymbols('PYSNMP-SOURCE-MIB', 'snmpSourceAddrTAddress')
+        snmpSourceAddrTAddress, = mibBuilder.importSymbols(
+            'PYSNMP-SOURCE-MIB', 'snmpSourceAddrTAddress')
 
         tblIdx = snmpTargetAddrEntry.getInstIdFromIndices(snmpTargetAddrName)
 
@@ -44,38 +45,46 @@ def getTargetAddr(snmpEngine, snmpTargetAddrName):
             snmpTargetAddrTDomain = snmpTargetAddrTDomain.getNode(
                 snmpTargetAddrTDomain.name + tblIdx
             ).syntax
+
             snmpTargetAddrTAddress = snmpTargetAddrTAddress.getNode(
                 snmpTargetAddrTAddress.name + tblIdx
             ).syntax
+
             snmpTargetAddrTimeout = snmpTargetAddrTimeout.getNode(
                 snmpTargetAddrTimeout.name + tblIdx
             ).syntax
+
             snmpTargetAddrRetryCount = snmpTargetAddrRetryCount.getNode(
                 snmpTargetAddrRetryCount.name + tblIdx
             ).syntax
+
             snmpTargetAddrParams = snmpTargetAddrParams.getNode(
                 snmpTargetAddrParams.name + tblIdx
             ).syntax
+
             snmpSourceAddrTAddress = snmpSourceAddrTAddress.getNode(
                 snmpSourceAddrTAddress.name + tblIdx
             ).syntax
+
         except NoSuchInstanceError:
             raise SmiError('Target %s not configured to LCD' % snmpTargetAddrName)
 
         transport = snmpEngine.transportDispatcher.getTransport(snmpTargetAddrTDomain)
 
         if snmpTargetAddrTDomain[:len(config.SNMP_UDP_DOMAIN)] == config.SNMP_UDP_DOMAIN:
-            SnmpUDPAddress, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMPv2-TM',
-                                                                                                    'SnmpUDPAddress')
+            SnmpUDPAddress, = mibBuilder.importSymbols('SNMPv2-TM', 'SnmpUDPAddress')
+
             snmpTargetAddrTAddress = transport.ADDRESS_TYPE(
                 SnmpUDPAddress(snmpTargetAddrTAddress)
             ).setLocalAddress(SnmpUDPAddress(snmpSourceAddrTAddress))
+
         elif snmpTargetAddrTDomain[:len(config.SNMP_UDP6_DOMAIN)] == config.SNMP_UDP6_DOMAIN:
-            TransportAddressIPv6, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
-                'TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
+            TransportAddressIPv6, = mibBuilder.importSymbols('TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
+
             snmpTargetAddrTAddress = transport.ADDRESS_TYPE(
                 TransportAddressIPv6(snmpTargetAddrTAddress)
             ).setLocalAddress(TransportAddressIPv6(snmpSourceAddrTAddress))
+
         elif snmpTargetAddrTDomain[:len(config.snmpLocalDomain)] == config.snmpLocalDomain:
             snmpTargetAddrTAddress = transport.ADDRESS_TYPE(
                 snmpTargetAddrTAddress
@@ -126,15 +135,19 @@ def getTargetParams(snmpEngine, paramsName):
             snmpTargetParamsMPModel = snmpTargetParamsMPModel.getNode(
                 snmpTargetParamsMPModel.name + tblIdx
             ).syntax
+
             snmpTargetParamsSecurityModel = snmpTargetParamsSecurityModel.getNode(
                 snmpTargetParamsSecurityModel.name + tblIdx
             ).syntax
+
             snmpTargetParamsSecurityName = snmpTargetParamsSecurityName.getNode(
                 snmpTargetParamsSecurityName.name + tblIdx
             ).syntax
+
             snmpTargetParamsSecurityLevel = snmpTargetParamsSecurityLevel.getNode(
                 snmpTargetParamsSecurityLevel.name + tblIdx
             ).syntax
+
         except NoSuchInstanceError:
             raise SmiError('Parameters %s not configured at LCD' % paramsName)
 
@@ -159,8 +172,8 @@ def getTargetInfo(snmpEngine, snmpTargetAddrName):
     (snmpTargetParamsMPModel,
      snmpTargetParamsSecurityModel,
      snmpTargetParamsSecurityName,
-     snmpTargetParamsSecurityLevel) = getTargetParams(snmpEngine,
-                                                      snmpTargetAddrParams)
+     snmpTargetParamsSecurityLevel) = getTargetParams(
+        snmpEngine, snmpTargetAddrParams)
 
     return (snmpTargetAddrTDomain, snmpTargetAddrTAddress,
             snmpTargetAddrTimeout, snmpTargetAddrRetryCount,
@@ -171,8 +184,8 @@ def getTargetInfo(snmpEngine, snmpTargetAddrName):
 def getNotificationInfo(snmpEngine, notificationTarget):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    snmpNotifyEntry, = mibBuilder.importSymbols('SNMP-NOTIFICATION-MIB',
-                                                'snmpNotifyEntry')
+    snmpNotifyEntry, = mibBuilder.importSymbols(
+        'SNMP-NOTIFICATION-MIB', 'snmpNotifyEntry')
 
     cache = snmpEngine.getUserContext('getNotificationInfo')
     if cache is None:
@@ -185,10 +198,8 @@ def getNotificationInfo(snmpEngine, notificationTarget):
     targetToNotifyMap = cache['targetToNotifyMap']
 
     if notificationTarget not in targetToNotifyMap:
-        (snmpNotifyTag,
-         snmpNotifyType) = mibBuilder.importSymbols('SNMP-NOTIFICATION-MIB',
-                                                    'snmpNotifyTag',
-                                                    'snmpNotifyType')
+        snmpNotifyTag, snmpNotifyType = mibBuilder.importSymbols(
+            'SNMP-NOTIFICATION-MIB', 'snmpNotifyTag', 'snmpNotifyType')
 
         tblIdx = snmpNotifyEntry.getInstIdFromIndices(notificationTarget)
 
@@ -196,6 +207,7 @@ def getNotificationInfo(snmpEngine, notificationTarget):
             snmpNotifyTag = snmpNotifyTag.getNode(
                 snmpNotifyTag.name + tblIdx
             ).syntax
+
             snmpNotifyType = snmpNotifyType.getNode(
                 snmpNotifyType.name + tblIdx
             ).syntax
@@ -216,8 +228,8 @@ def getNotificationInfo(snmpEngine, notificationTarget):
 def getTargetNames(snmpEngine, tag):
     mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-    snmpTargetAddrEntry, = mibBuilder.importSymbols('SNMP-TARGET-MIB',
-                                                    'snmpTargetAddrEntry')
+    snmpTargetAddrEntry, = mibBuilder.importSymbols(
+        'SNMP-TARGET-MIB', 'snmpTargetAddrEntry')
 
     cache = snmpEngine.getUserContext('getTargetNames')
     if cache is None:
@@ -226,6 +238,7 @@ def getTargetNames(snmpEngine, tag):
 
     if cache['id'] == snmpTargetAddrEntry.branchVersionId:
         tagToTargetsMap = cache['tagToTargetsMap']
+
     else:
         cache['tagToTargetsMap'] = {}
 
@@ -236,10 +249,13 @@ def getTargetNames(snmpEngine, tag):
             'SNMP-TARGET-MIB', 'SnmpTagValue', 'snmpTargetAddrName',
             'snmpTargetAddrTagList'
         )
+
         mibNode = snmpTargetAddrTagList
+
         while True:
             try:
                 mibNode = snmpTargetAddrTagList.getNextNode(mibNode.name)
+
             except NoSuchInstanceError:
                 break
 
@@ -249,8 +265,10 @@ def getTargetNames(snmpEngine, tag):
 
             for _tag in mibNode.syntax.asOctets().split():
                 _tag = SnmpTagValue(_tag)
+
                 if _tag not in tagToTargetsMap:
                     tagToTargetsMap[_tag] = []
+
                 tagToTargetsMap[_tag].append(_snmpTargetAddrName)
 
         cache['id'] = snmpTargetAddrEntry.branchVersionId
diff --git a/pysnmp/entity/rfc3413/context.py b/pysnmp/entity/rfc3413/context.py
index 9a99f284..8c759075 100644
--- a/pysnmp/entity/rfc3413/context.py
+++ b/pysnmp/entity/rfc3413/context.py
@@ -13,14 +13,20 @@ from pysnmp import error
 
 class SnmpContext(object):
     def __init__(self, snmpEngine, contextEngineId=None):
-        snmpEngineId, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                              'snmpEngineID')
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+
         if contextEngineId is None:
             # Default to local snmpEngineId
             self.contextEngineId = snmpEngineId.syntax
+
         else:
             self.contextEngineId = snmpEngineId.syntax.clone(contextEngineId)
-        debug.logger & debug.FLAG_INS and debug.logger('SnmpContext: contextEngineId \"%r\"' % (self.contextEngineId,))
+
+        debug.logger & debug.FLAG_INS and debug.logger(
+            'SnmpContext: contextEngineId %r' % (self.contextEngineId,))
+
         self.contextNames = {
             null: snmpEngine.msgAndPduDsp.mibInstrumController  # Default name
         }
@@ -29,30 +35,35 @@ class SnmpContext(object):
         contextName = univ.OctetString(contextName).asOctets()
         if contextName in self.contextNames:
             raise error.PySnmpError(
-                'Duplicate contextName %s' % contextName
-            )
+                'Duplicate contextName %s' % contextName)
+
         debug.logger & debug.FLAG_INS and debug.logger(
             'registerContextName: registered contextName %r, mibInstrum %r' % (contextName, mibInstrum))
+
         if mibInstrum is None:
             self.contextNames[contextName] = self.contextNames[null]
+
         else:
             self.contextNames[contextName] = mibInstrum
 
     def unregisterContextName(self, contextName):
         contextName = univ.OctetString(contextName).asOctets()
+
         if contextName in self.contextNames:
             debug.logger & debug.FLAG_INS and debug.logger(
                 'unregisterContextName: unregistered contextName %r' % contextName)
+
             del self.contextNames[contextName]
 
     def getMibInstrum(self, contextName=null):
         contextName = univ.OctetString(contextName).asOctets()
         if contextName not in self.contextNames:
             debug.logger & debug.FLAG_INS and debug.logger('getMibInstrum: contextName %r not registered' % contextName)
-            raise error.PySnmpError(
-                'Missing contextName %s' % contextName
-            )
+
+            raise error.PySnmpError('Missing contextName %s' % contextName)
+
         else:
             debug.logger & debug.FLAG_INS and debug.logger(
                 'getMibInstrum: contextName %r, mibInstum %r' % (contextName, self.contextNames[contextName]))
+
             return self.contextNames[contextName]
diff --git a/pysnmp/entity/rfc3413/ntforg.py b/pysnmp/entity/rfc3413/ntforg.py
index e73dbf19..fc1e8c0a 100644
--- a/pysnmp/entity/rfc3413/ntforg.py
+++ b/pysnmp/entity/rfc3413/ntforg.py
@@ -29,6 +29,7 @@ class NotificationOriginator(object):
                            securityModel, securityName, securityLevel,
                            contextEngineId, contextName, pduVersion,
                            PDU, statusInformation, sendPduHandle, cbInfo):
+
         sendRequestHandle, cbFun, cbCtx = cbInfo
 
         # 3.3.6d
@@ -39,38 +40,48 @@ class NotificationOriginator(object):
          origMessageProcessingModel, origSecurityModel,
          origSecurityName, origSecurityLevel, origContextEngineId,
          origContextName, origPdu, origTimeout,
-         origRetryCount, origRetries, origDiscoveryRetries) = self.__pendingReqs.pop(sendPduHandle)
+         origRetryCount, origRetries,
+         origDiscoveryRetries) = self.__pendingReqs.pop(sendPduHandle)
 
         snmpEngine.transportDispatcher.jobFinished(id(self))
 
         if statusInformation:
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponsePdu: sendRequestHandle %s, sendPduHandle %s statusInformation %s' % (
-                    sendRequestHandle, sendPduHandle, statusInformation))
+                'processResponsePdu: sendRequestHandle %s, sendPduHandle %s '
+                'statusInformation %s' % (sendRequestHandle, sendPduHandle,
+                                          statusInformation))
 
             errorIndication = statusInformation['errorIndication']
 
             if errorIndication in (errind.notInTimeWindow, errind.unknownEngineID):
                 origDiscoveryRetries += 1
                 origRetries = 0
+
             else:
                 origDiscoveryRetries = 0
                 origRetries += 1
 
-            if origRetries > origRetryCount or origDiscoveryRetries > self.__options.get('discoveryRetries', 4):
+            if (origRetries > origRetryCount or
+                    origDiscoveryRetries > self.__options.get('discoveryRetries', 4)):
+
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'processResponsePdu: sendRequestHandle %s, sendPduHandle %s retry count %d exceeded' % (
+                    'processResponsePdu: sendRequestHandle %s, sendPduHandle %s '
+                    'retry count %d exceeded' % (
                         sendRequestHandle, sendPduHandle, origRetries))
+
                 cbFun(snmpEngine, sendRequestHandle, errorIndication, None, cbCtx)
+
                 return
 
             # Convert timeout in seconds into timeout in timer ticks
-            timeoutInTicks = float(origTimeout) / 100 / snmpEngine.transportDispatcher.getTimerResolution()
+            timeoutInTicks = (float(origTimeout) / 100 /
+                              snmpEngine.transportDispatcher.getTimerResolution())
 
             # User-side API assumes SMIv2
             if messageProcessingModel == 0:
                 reqPDU = rfc2576.v2ToV1(origPdu)
                 pduVersion = 0
+
             else:
                 reqPDU = origPdu
                 pduVersion = 1
@@ -85,20 +96,26 @@ class NotificationOriginator(object):
                     reqPDU, True, timeoutInTicks, self.processResponsePdu,
                     (sendRequestHandle, cbFun, cbCtx)
                 )
+
             except error.StatusInformation as exc:
                 statusInformation = exc
+
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'processResponsePdu: sendRequestHandle %s: sendPdu() failed with %r ' % (
-                        sendRequestHandle, statusInformation))
+                    'processResponsePdu: sendRequestHandle %s: sendPdu() '
+                    'failed with %r ' % (sendRequestHandle, statusInformation))
+
                 cbFun(snmpEngine, sendRequestHandle,
                       statusInformation['errorIndication'], None, cbCtx)
+
                 return
 
             snmpEngine.transportDispatcher.jobStarted(id(self))
 
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponsePdu: sendRequestHandle %s, sendPduHandle %s, timeout %d, retry %d of %d' % (
-                    sendRequestHandle, sendPduHandle, origTimeout, origRetries, origRetryCount))
+                'processResponsePdu: sendRequestHandle %s, sendPduHandle %s, '
+                'timeout %d, retry %d of %d' % (
+                    sendRequestHandle, sendPduHandle, origTimeout, origRetries,
+                    origRetryCount))
 
             # 3.3.6b
             self.__pendingReqs[sendPduHandle] = (
@@ -108,6 +125,7 @@ class NotificationOriginator(object):
                 origContextEngineId, origContextName, origPdu,
                 origTimeout, origRetryCount, origRetries, origDiscoveryRetries
             )
+
             return
 
         # 3.3.6c
@@ -129,6 +147,7 @@ class NotificationOriginator(object):
         if messageProcessingModel == 0:
             reqPDU = rfc2576.v2ToV1(pdu)
             pduVersion = 0
+
         else:
             reqPDU = pdu
             pduVersion = 1
@@ -136,7 +155,8 @@ class NotificationOriginator(object):
         # 3.3.5
         if reqPDU.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             # Convert timeout in seconds into timeout in timer ticks
-            timeoutInTicks = float(timeout) / 100 / snmpEngine.transportDispatcher.getTimerResolution()
+            timeoutInTicks = (float(timeout) / 100 /
+                              snmpEngine.transportDispatcher.getTimerResolution())
 
             sendRequestHandle = getNextHandle()
 
@@ -158,7 +178,9 @@ class NotificationOriginator(object):
                 securityModel, securityName, securityLevel, contextEngineId,
                 contextName, pdu, timeout, retryCount, 0, 0
             )
+
             snmpEngine.transportDispatcher.jobStarted(id(self))
+
         else:
             snmpEngine.msgAndPduDsp.sendPdu(
                 snmpEngine, transportDomain, transportAddress,
@@ -180,14 +202,18 @@ class NotificationOriginator(object):
         self.__pendingNotifications[notificationHandle].remove(sendRequestHandle)
 
         debug.logger & debug.FLAG_APP and debug.logger(
-            'processResponseVarBinds: notificationHandle %s, sendRequestHandle %s, errorIndication %s, pending requests %s' % (
-                notificationHandle, sendRequestHandle, errorIndication, self.__pendingNotifications[notificationHandle]))
+            'processResponseVarBinds: notificationHandle %s, sendRequestHandle %s, '
+            'errorIndication %s, pending requests %s' % (
+                notificationHandle, sendRequestHandle, errorIndication,
+                self.__pendingNotifications[notificationHandle]))
 
         if not self.__pendingNotifications[notificationHandle]:
             debug.logger & debug.FLAG_APP and debug.logger(
-                'processResponseVarBinds: notificationHandle %s, sendRequestHandle %s -- completed' % (
-                    notificationHandle, sendRequestHandle))
+                'processResponseVarBinds: notificationHandle %s, sendRequestHandle %s '
+                '-- completed' % (notificationHandle, sendRequestHandle))
+
             del self.__pendingNotifications[notificationHandle]
+
             cbFun(snmpEngine, sendRequestHandle, errorIndication,
                   pdu and v2c.apiPDU.getErrorStatus(pdu) or 0,
                   pdu and v2c.apiPDU.getErrorIndex(pdu, muteErrors=True) or 0,
@@ -198,11 +224,14 @@ class NotificationOriginator(object):
     # Higher-level API to Notification Originator. Supports multiple
     # targets, automatic var-binding formation and is fully LCD-driven.
     #
+
     def sendVarBinds(self, snmpEngine, notificationTarget, contextEngineId,
                      contextName, varBinds=(), cbFun=None, cbCtx=None):
         debug.logger & debug.FLAG_APP and debug.logger(
-            'sendVarBinds: notificationTarget %s, contextEngineId %s, contextName "%s", varBinds %s' % (
-                notificationTarget, contextEngineId or '<default>', contextName, varBinds))
+            'sendVarBinds: notificationTarget %s, contextEngineId %s, '
+            'contextName "%s", varBinds %s' % (
+                notificationTarget, contextEngineId or '<default>',
+                contextName, varBinds))
 
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
@@ -251,6 +280,7 @@ class NotificationOriginator(object):
                 del varBinds[idx + 2]
                 if varBinds[1][0] == snmpTrapOID:
                     varBinds[1] = varBind
+
                 else:
                     varBinds.insert(1, varBind)
                 break
@@ -261,12 +291,14 @@ class NotificationOriginator(object):
 
         sendRequestHandle = -1
 
-        debug.logger & debug.FLAG_APP and debug.logger('sendVarBinds: final varBinds %s' % (varBinds,))
+        debug.logger & debug.FLAG_APP and debug.logger(
+            'sendVarBinds: final varBinds %s' % (varBinds,))
 
         for targetAddrName in config.getTargetNames(snmpEngine, notifyTag):
             (transportDomain, transportAddress, timeout,
              retryCount, params) = config.getTargetAddr(snmpEngine,
                                                         targetAddrName)
+
             (messageProcessingModel, securityModel, securityName,
              securityLevel) = config.getTargetParams(snmpEngine, params)
 
@@ -278,13 +310,16 @@ class NotificationOriginator(object):
             #              filterType) = config.getNotifyFilter(filterProfileName)
 
             debug.logger & debug.FLAG_APP and debug.logger(
-                'sendVarBinds: notificationHandle %s, notifyTag %s yields: transportDomain %s, transportAddress %r, securityModel %s, securityName %s, securityLevel %s' % (
-                    notificationHandle, notifyTag, transportDomain, transportAddress, securityModel,
-                    securityName, securityLevel))
+                'sendVarBinds: notificationHandle %s, notifyTag %s yields: '
+                'transportDomain %s, transportAddress %r, securityModel %s, '
+                'securityName %s, securityLevel %s' % (
+                    notificationHandle, notifyTag, transportDomain, transportAddress,
+                    securityModel, securityName, securityLevel))
 
             for varName, varVal in varBinds:
                 if varName in (sysUpTime, snmpTrapOID):
                     continue
+
                 try:
                     snmpEngine.accessControlModel[self.ACM_ID].isAccessAllowed(
                         snmpEngine, securityModel, securityName,
@@ -292,19 +327,22 @@ class NotificationOriginator(object):
                     )
 
                     debug.logger & debug.FLAG_APP and debug.logger(
-                        'sendVarBinds: ACL succeeded for OID %s securityName %s' % (varName, securityName))
+                        'sendVarBinds: ACL succeeded for OID %s securityName %s' % (
+                            varName, securityName))
 
                 except error.StatusInformation:
                     debug.logger & debug.FLAG_APP and debug.logger(
-                        'sendVarBinds: ACL denied access for OID %s securityName %s, droppping notification' % (
-                            varName, securityName))
+                        'sendVarBinds: ACL denied access for OID %s securityName %s,'
+                        'dropping notification' % (varName, securityName))
                     return
 
             # 3.3.4
             if notifyType == 1:
                 pdu = v2c.SNMPv2TrapPDU()
+
             elif notifyType == 2:
                 pdu = v2c.InformRequestPDU()
+
             else:
                 raise error.ProtocolError('Unknown notify-type %r', notifyType)
 
@@ -321,22 +359,27 @@ class NotificationOriginator(object):
 
             except error.StatusInformation as exc:
                 statusInformation = exc
+
                 debug.logger & debug.FLAG_APP and debug.logger(
-                    'sendVarBinds: sendRequestHandle %s: sendPdu() failed with %r' % (
-                        sendRequestHandle, statusInformation))
-                if notificationHandle not in self.__pendingNotifications or \
-                        not self.__pendingNotifications[notificationHandle]:
+                    'sendVarBinds: sendRequestHandle %s: sendPdu() failed '
+                    'with %r' % (sendRequestHandle, statusInformation))
+
+                if (notificationHandle not in self.__pendingNotifications or
+                        not self.__pendingNotifications[notificationHandle]):
+
                     if notificationHandle in self.__pendingNotifications:
                         del self.__pendingNotifications[notificationHandle]
+
                     if cbFun:
                         cbFun(snmpEngine, notificationHandle,
                               statusInformation['errorIndication'], 0, 0, (),
                               cbCtx)
+
                 return notificationHandle
 
             debug.logger & debug.FLAG_APP and debug.logger(
-                'sendVarBinds: notificationHandle %s, sendRequestHandle %s, timeout %d' % (
-                    notificationHandle, sendRequestHandle, timeout))
+                'sendVarBinds: notificationHandle %s, sendRequestHandle %s, '
+                'timeout %d' % (notificationHandle, sendRequestHandle, timeout))
 
             if notifyType == 2:
                 if notificationHandle not in self.__pendingNotifications:
@@ -344,8 +387,8 @@ class NotificationOriginator(object):
                 self.__pendingNotifications[notificationHandle].add(sendRequestHandle)
 
         debug.logger & debug.FLAG_APP and debug.logger(
-            'sendVarBinds: notificationHandle %s, sendRequestHandle %s, notification(s) sent' % (
-                notificationHandle, sendRequestHandle))
+            'sendVarBinds: notificationHandle %s, sendRequestHandle %s, '
+            'notification(s) sent' % (notificationHandle, sendRequestHandle))
 
         return notificationHandle
 
diff --git a/pysnmp/entity/rfc3413/ntfrcv.py b/pysnmp/entity/rfc3413/ntfrcv.py
index a4754be2..53cc7ac3 100644
--- a/pysnmp/entity/rfc3413/ntfrcv.py
+++ b/pysnmp/entity/rfc3413/ntfrcv.py
@@ -31,7 +31,8 @@ class NotificationReceiver(object):
         def storeSnmpTrapCommunity(snmpEngine, execpoint, variables, cbCtx):
             self.__snmpTrapCommunity = variables.get('communityName', '')
 
-        snmpEngine.observer.registerObserver(storeSnmpTrapCommunity, 'rfc2576.processIncomingMsg')
+        snmpEngine.observer.registerObserver(
+            storeSnmpTrapCommunity, 'rfc2576.processIncomingMsg')
 
     def close(self, snmpEngine):
         snmpEngine.msgAndPduDsp.unregisterContextEngineId(
@@ -48,6 +49,7 @@ class NotificationReceiver(object):
         if messageProcessingModel == 0:
             origPdu = PDU
             PDU = rfc2576.v1ToV2(PDU, snmpTrapCommunity=self.__snmpTrapCommunity)
+
         else:
             origPdu = None
 
@@ -89,12 +91,17 @@ class NotificationReceiver(object):
             except error.StatusInformation as exc:
                 debug.logger & debug.FLAG_APP and debug.logger(
                     'processPdu: stateReference %s, statusInformation %s' % (stateReference, exc))
-                snmpSilentDrops, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB',
-                                                                                                         'snmpSilentDrops')
+
+                mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+                snmpSilentDrops, = mibBuilder.importSymbols(
+                    '__SNMPv2-MIB', 'snmpSilentDrops')
+
                 snmpSilentDrops.syntax += 1
 
         elif PDU.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
             pass
+
         else:
             raise error.ProtocolError('Unexpected PDU class %s' % PDU.tagSet)
 
diff --git a/pysnmp/hlapi/transport.py b/pysnmp/hlapi/transport.py
index 20471633..d75951c6 100644
--- a/pysnmp/hlapi/transport.py
+++ b/pysnmp/hlapi/transport.py
@@ -27,8 +27,7 @@ class AbstractTransportTarget(object):
     def __repr__(self):
         return '%s(%r, timeout=%r, retries=%r, tagList=%r)' % (
             self.__class__.__name__, self.transportAddr,
-            self.timeout, self.retries, self.tagList
-        )
+            self.timeout, self.retries, self.tagList)
 
     def getTransportInfo(self):
         return self.TRANSPORT_DOMAIN, self.transportAddr
@@ -55,9 +54,11 @@ class AbstractTransportTarget(object):
         return self.transport
 
     def verifyDispatcherCompatibility(self, snmpEngine):
-        if not self.PROTO_TRANSPORT.isCompatibleWithDispatcher(snmpEngine.transportDispatcher):
-            raise error.PySnmpError('Transport %r is not compatible with dispatcher %r' % (
-                self.PROTO_TRANSPORT, snmpEngine.transportDispatcher))
+        if not self.PROTO_TRANSPORT.isCompatibleWithDispatcher(
+                snmpEngine.transportDispatcher):
+            raise error.PySnmpError(
+                'Transport %r is not compatible with dispatcher '
+                '%r' % (self.PROTO_TRANSPORT, snmpEngine.transportDispatcher))
 
     def _resolveAddr(self, transportAddr):
         raise NotImplementedError()
diff --git a/pysnmp/hlapi/v1arch/asyncio/cmdgen.py b/pysnmp/hlapi/v1arch/asyncio/cmdgen.py
index 346b7c76..3e53c05b 100644
--- a/pysnmp/hlapi/v1arch/asyncio/cmdgen.py
+++ b/pysnmp/hlapi/v1arch/asyncio/cmdgen.py
@@ -4,18 +4,18 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-from pysnmp.hlapi.v1arch.auth import *
-from pysnmp.hlapi.varbinds import *
-from pysnmp.hlapi.v1arch.asyncio.transport import *
-from pysnmp.smi.rfc1902 import *
-from pysnmp.proto import api
-
 try:
     import asyncio
 
 except ImportError:
     import trollius as asyncio
 
+from pysnmp.hlapi.v1arch.auth import *
+from pysnmp.hlapi.varbinds import *
+from pysnmp.hlapi.v1arch.asyncio.transport import *
+from pysnmp.smi.rfc1902 import *
+from pysnmp.proto import api
+
 __all__ = ['getCmd', 'nextCmd', 'setCmd', 'bulkCmd', 'isEndOfMib']
 
 VB_PROCESSOR = CommandGeneratorVarBinds()
diff --git a/pysnmp/hlapi/v1arch/asyncore/cmdgen.py b/pysnmp/hlapi/v1arch/asyncore/cmdgen.py
index e7ddadb2..3a1de67f 100644
--- a/pysnmp/hlapi/v1arch/asyncore/cmdgen.py
+++ b/pysnmp/hlapi/v1arch/asyncore/cmdgen.py
@@ -4,7 +4,6 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-
 from pysnmp.hlapi.v1arch.auth import *
 from pysnmp.hlapi.v1arch.asyncore import *
 from pysnmp.hlapi.varbinds import *
diff --git a/pysnmp/hlapi/v1arch/asyncore/sync/cmdgen.py b/pysnmp/hlapi/v1arch/asyncore/sync/cmdgen.py
index a1c3366d..2961a63a 100644
--- a/pysnmp/hlapi/v1arch/asyncore/sync/cmdgen.py
+++ b/pysnmp/hlapi/v1arch/asyncore/sync/cmdgen.py
@@ -4,11 +4,10 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-from pyasn1.type.univ import Null
-
 from pysnmp.hlapi.v1arch.asyncore import cmdgen
 from pysnmp.hlapi.varbinds import *
 from pysnmp.proto.rfc1905 import endOfMibView
+from pysnmp.proto.rfc1902 import Null
 
 __all__ = ['getCmd', 'nextCmd', 'setCmd', 'bulkCmd']
 
diff --git a/pysnmp/hlapi/v3arch/asyncio/cmdgen.py b/pysnmp/hlapi/v3arch/asyncio/cmdgen.py
index 89420cb2..29d2ca63 100644
--- a/pysnmp/hlapi/v3arch/asyncio/cmdgen.py
+++ b/pysnmp/hlapi/v3arch/asyncio/cmdgen.py
@@ -31,6 +31,12 @@
 # ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 # THE POSSIBILITY OF SUCH DAMAGE.
 #
+try:
+    import asyncio
+
+except ImportError:
+    import trollius as asyncio
+
 from pysnmp.hlapi.v3arch.auth import *
 from pysnmp.hlapi.v3arch.context import *
 from pysnmp.hlapi.v3arch.lcd import *
@@ -40,12 +46,6 @@ from pysnmp.entity.rfc3413 import cmdgen
 from pysnmp.proto.api import v2c
 from pysnmp.smi.rfc1902 import *
 
-try:
-    import asyncio
-
-except ImportError:
-    import trollius as asyncio
-
 __all__ = ['getCmd', 'nextCmd', 'setCmd', 'bulkCmd', 'isEndOfMib']
 
 VB_PROCESSOR = CommandGeneratorVarBinds()
@@ -134,17 +134,20 @@ def getCmd(snmpEngine, authData, transportTarget, contextData,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
         lookupMib, future = cbCtx
+
         if future.cancelled():
             return
+
         try:
-            varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds,
-                                                         lookupMib)
+            varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(
+                snmpEngine.cache, varBinds, lookupMib)
+
         except Exception as e:
             future.set_exception(e)
+
         else:
             future.set_result(
-                (errorIndication, errorStatus, errorIndex, varBindsUnmade)
-            )
+                (errorIndication, errorStatus, errorIndex, varBindsUnmade))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
@@ -157,6 +160,7 @@ def getCmd(snmpEngine, authData, transportTarget, contextData,
         VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
         (options.get('lookupMib', True), future)
     )
+
     return future
 
 
@@ -240,13 +244,17 @@ def setCmd(snmpEngine, authData, transportTarget, contextData,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
         lookupMib, future = cbCtx
+
         if future.cancelled():
             return
+
         try:
-            varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds,
-                                                         lookupMib)
+            varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(
+                snmpEngine.cache, varBinds, lookupMib)
+
         except Exception as e:
             future.set_exception(e)
+
         else:
             future.set_result(
                 (errorIndication, errorStatus, errorIndex, varBindsUnmade)
@@ -263,6 +271,7 @@ def setCmd(snmpEngine, authData, transportTarget, contextData,
         VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
         (options.get('lookupMib', True), future)
     )
+
     return future
 
 
@@ -352,17 +361,20 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
         lookupMib, future = cbCtx
         if future.cancelled():
             return
+
         try:
-            varBindsUnmade = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
-                                                          varBindTableRow,
-                                                          lookupMib)
-                              for varBindTableRow in varBindTable]
+            varBindsUnmade = [
+                VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBindTableRow,
+                                            lookupMib)
+                for varBindTableRow in varBindTable
+            ]
+
         except Exception as e:
             future.set_exception(e)
+
         else:
             future.set_result(
-                (errorIndication, errorStatus, errorIndex, varBindsUnmade)
-            )
+                (errorIndication, errorStatus, errorIndex, varBindsUnmade))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
@@ -375,6 +387,7 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
         VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
         (options.get('lookupMib', True), future)
     )
+
     return future
 
 
@@ -491,20 +504,23 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
                 errorIndication, errorStatus, errorIndex,
                 varBindTable, cbCtx):
         lookupMib, future = cbCtx
+
         if future.cancelled():
             return
+
         try:
-            varBindsUnmade = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
-                                                          varBindTableRow,
-                                                          lookupMib)
-                              for varBindTableRow in varBindTable]
+            varBindsUnmade = [
+                VB_PROCESSOR.unmakeVarBinds(
+                    snmpEngine.cache, varBindTableRow, lookupMib)
+                for varBindTableRow in varBindTable
+            ]
+
         except Exception as e:
             future.set_exception(e)
 
         else:
             future.set_result(
-                (errorIndication, errorStatus, errorIndex, varBindsUnmade)
-            )
+                (errorIndication, errorStatus, errorIndex, varBindsUnmade))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
@@ -517,4 +533,5 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
         VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
         (options.get('lookupMib', True), future)
     )
+
     return future
diff --git a/pysnmp/hlapi/v3arch/asyncio/transport.py b/pysnmp/hlapi/v3arch/asyncio/transport.py
index 0b795163..f897de09 100644
--- a/pysnmp/hlapi/v3arch/asyncio/transport.py
+++ b/pysnmp/hlapi/v3arch/asyncio/transport.py
@@ -56,11 +56,11 @@ class UdpTransportTarget(AbstractTransportTarget):
 
     def _resolveAddr(self, transportAddr):
         try:
-            return socket.getaddrinfo(transportAddr[0],
-                                      transportAddr[1],
-                                      socket.AF_INET,
-                                      socket.SOCK_DGRAM,
-                                      socket.IPPROTO_UDP)[0][4][:2]
+            return socket.getaddrinfo(
+                transportAddr[0], transportAddr[1],
+                socket.AF_INET, socket.SOCK_DGRAM,
+                socket.IPPROTO_UDP)[0][4][:2]
+
         except socket.gaierror as exc:
             raise PySnmpError('Bad IPv4/UDP transport address %s: %s' % (
                 '@'.join([str(x) for x in transportAddr]), exc))
@@ -116,11 +116,11 @@ class Udp6TransportTarget(AbstractTransportTarget):
 
     def _resolveAddr(self, transportAddr):
         try:
-            return socket.getaddrinfo(transportAddr[0],
-                                      transportAddr[1],
-                                      socket.AF_INET6,
-                                      socket.SOCK_DGRAM,
-                                      socket.IPPROTO_UDP)[0][4][:2]
+            return socket.getaddrinfo(
+                transportAddr[0], transportAddr[1],
+                socket.AF_INET6, socket.SOCK_DGRAM,
+                socket.IPPROTO_UDP)[0][4][:2]
+
         except socket.gaierror as exc:
             raise PySnmpError('Bad IPv6/UDP transport address %s: %s' % (
                 '@'.join([str(x) for x in transportAddr]), exc))
diff --git a/pysnmp/hlapi/v3arch/asyncore/cmdgen.py b/pysnmp/hlapi/v3arch/asyncore/cmdgen.py
index 6446bce5..e11e040e 100644
--- a/pysnmp/hlapi/v3arch/asyncore/cmdgen.py
+++ b/pysnmp/hlapi/v3arch/asyncore/cmdgen.py
@@ -113,24 +113,26 @@ def getCmd(snmpEngine, authData, transportTarget, contextData,
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
+
         lookupMib, cbFun, cbCtx = cbCtx
+
         if cbFun:
+            varBinds = VB_PROCESSOR.unmakeVarBinds(
+                snmpEngine.cache, varBinds, lookupMib)
+
             return cbFun(snmpEngine, sendRequestHandle, errorIndication,
-                         errorStatus, errorIndex,
-                         VB_PROCESSOR.unmakeVarBinds(
-                             snmpEngine.cache, varBinds, lookupMib
-                         ), cbCtx)
+                         errorStatus, errorIndex, varBinds, cbCtx)
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     return cmdgen.GetCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
-        contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
+        contextData.contextName, varBinds, __cbFun,
         (options.get('lookupMib', True),
-         options.get('cbFun'), options.get('cbCtx'))
-    )
+         options.get('cbFun'), options.get('cbCtx')))
 
 
 def setCmd(snmpEngine, authData, transportTarget, contextData,
@@ -226,22 +228,25 @@ def setCmd(snmpEngine, authData, transportTarget, contextData,
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
+
         lookupMib, cbFun, cbCtx = cbCtx
+
+        varBinds = VB_PROCESSOR.unmakeVarBinds(
+            snmpEngine.cache, varBinds, lookupMib)
+
         return cbFun(snmpEngine, sendRequestHandle, errorIndication,
-                     errorStatus, errorIndex,
-                     VB_PROCESSOR.unmakeVarBinds(
-                         snmpEngine.cache, varBinds, lookupMib
-                     ), cbCtx)
+                     errorStatus, errorIndex, varBinds, cbCtx)
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     return cmdgen.SetCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
-        contextData.contextName, VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds),
+        contextData.contextName, varBinds,
         __cbFun, (options.get('lookupMib', True),
-                  options.get('cbFun'), options.get('cbCtx'))
-    )
+                  options.get('cbFun'), options.get('cbCtx')))
 
 
 def nextCmd(snmpEngine, authData, transportTarget, contextData,
@@ -338,23 +343,26 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
 
     def __cbFun(snmpEngine, sendRequestHandle, errorIndication,
                 errorStatus, errorIndex, varBindTable, cbCtx):
+
         lookupMib, cbFun, cbCtx = cbCtx
+
+        varBindTable = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
+                                                    varBindTableRow, lookupMib)
+                        for varBindTableRow in varBindTable]
+
         return cbFun(snmpEngine, sendRequestHandle, errorIndication,
-                     errorStatus, errorIndex,
-                     [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBindTableRow, lookupMib) for varBindTableRow in
-                      varBindTable],
-                     cbCtx)
+                     errorStatus, errorIndex, varBindTable, cbCtx)
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     return cmdgen.NextCommandGenerator().sendVarBinds(
-        snmpEngine, addrName,
-        contextData.contextEngineId, contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds),
-        __cbFun, (options.get('lookupMib', True),
-                  options.get('cbFun'), options.get('cbCtx'))
-    )
+        snmpEngine, addrName, contextData.contextEngineId,
+        contextData.contextName, varBinds, __cbFun,
+        (options.get('lookupMib', True), options.get('cbFun'),
+         options.get('cbCtx')))
 
 
 def bulkCmd(snmpEngine, authData, transportTarget, contextData,
@@ -481,19 +489,23 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBindTable, cbCtx):
+
         lookupMib, cbFun, cbCtx = cbCtx
+
+        varBindTable = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
+                                                    varBindTableRow, lookupMib)
+                        for varBindTableRow in varBindTable]
+
         return cbFun(snmpEngine.cache, sendRequestHandle, errorIndication,
-                     errorStatus, errorIndex,
-                     [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBindTableRow, lookupMib) for varBindTableRow in
-                      varBindTable], cbCtx)
+                     errorStatus, errorIndex, varBindTable, cbCtx)
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     return cmdgen.BulkCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
         contextData.contextName, nonRepeaters, maxRepetitions,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
-        (options.get('lookupMib', True),
-         options.get('cbFun'), options.get('cbCtx'))
-    )
+        varBinds, __cbFun, (options.get('lookupMib', True),
+                            options.get('cbFun'), options.get('cbCtx')))
diff --git a/pysnmp/hlapi/v3arch/asyncore/ntforg.py b/pysnmp/hlapi/v3arch/asyncore/ntforg.py
index 7df0bc08..2e714c08 100644
--- a/pysnmp/hlapi/v3arch/asyncore/ntforg.py
+++ b/pysnmp/hlapi/v3arch/asyncore/ntforg.py
@@ -152,22 +152,23 @@ def sendNotification(snmpEngine, authData, transportTarget, contextData,
     # noinspection PyShadowingNames
     def __cbFun(snmpEngine, sendRequestHandle, errorIndication,
                 errorStatus, errorIndex, varBinds, cbCtx):
+
         lookupMib, cbFun, cbCtx = cbCtx
+
+        varBinds = VB_PROCESSOR.unmakeVarBinds(
+            snmpEngine.cache, varBinds, lookupMib)
+
         return cbFun and cbFun(
             snmpEngine, sendRequestHandle, errorIndication,
-            errorStatus, errorIndex,
-            VB_PROCESSOR.unmakeVarBinds(
-                snmpEngine.cache, varBinds, lookupMib
-            ), cbCtx
-        )
+            errorStatus, errorIndex, varBinds, cbCtx)
 
     notifyName = LCD.configure(snmpEngine, authData, transportTarget,
                                notifyType, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     return ntforg.NotificationOriginator().sendVarBinds(
         snmpEngine, notifyName,
         contextData.contextEngineId, contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
-        (options.get('lookupMib', True),
-         options.get('cbFun'), options.get('cbCtx'))
-    )
+        varBinds, __cbFun, (options.get('lookupMib', True),
+                            options.get('cbFun'), options.get('cbCtx')))
diff --git a/pysnmp/hlapi/v3arch/asyncore/sync/cmdgen.py b/pysnmp/hlapi/v3arch/asyncore/sync/cmdgen.py
index c0e7a379..6165fa33 100644
--- a/pysnmp/hlapi/v3arch/asyncore/sync/cmdgen.py
+++ b/pysnmp/hlapi/v3arch/asyncore/sync/cmdgen.py
@@ -108,6 +108,7 @@ def getCmd(snmpEngine, authData, transportTarget, contextData,
             errorStatus = cbCtx['errorStatus']
             errorIndex = cbCtx['errorIndex']
             varBinds = cbCtx['varBinds']
+
         else:
             errorIndication = errorStatus = errorIndex = None
             varBinds = []
@@ -214,6 +215,7 @@ def setCmd(snmpEngine, authData, transportTarget, contextData,
             errorStatus = cbCtx['errorStatus']
             errorIndex = cbCtx['errorIndex']
             varBinds = cbCtx['varBinds']
+
         else:
             errorIndication = errorStatus = errorIndex = None
             varBinds = []
@@ -363,6 +365,7 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
             if errorIndication:
                 yield (errorIndication, errorStatus, errorIndex, varBinds)
                 return
+
             elif errorStatus:
                 if errorStatus == 2:
                     # Hide SNMPv1 noSuchName error which leaks in here
@@ -371,6 +374,7 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
                     errorIndex = errorIndex.clone(0)
                 yield (errorIndication, errorStatus, errorIndex, varBinds)
                 return
+
             else:
                 stopFlag = True
 
@@ -570,8 +574,10 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
         if errorIndication:
             yield (errorIndication, errorStatus, errorIndex,
                    varBindTable and varBindTable[0] or [])
+
             if errorIndication != errind.requestTimedOut:
                 return
+
         elif errorStatus:
             if errorStatus == 2:
                 # Hide SNMPv1 noSuchName error which leaks in here
@@ -580,26 +586,35 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
                 errorIndex = errorIndex.clone(0)
             yield (errorIndication, errorStatus, errorIndex, varBindTable and varBindTable[0] or [])
             return
+
         else:
             for row in range(len(varBindTable)):
                 stopFlag = True
+
                 if len(varBindTable[row]) != len(initialVars):
                     varBindTable = row and varBindTable[:row - 1] or []
                     break
+
                 for col in range(len(varBindTable[row])):
                     name, val = varBindTable[row][col]
+
                     if row:
                         previousVarBinds = varBindTable[row - 1]
+
                     if nullVarBinds[col]:
                         varBindTable[row][col] = previousVarBinds[col][0], endOfMibView
                         continue
+
                     stopFlag = False
+
                     if isinstance(val, Null):
                         varBindTable[row][col] = previousVarBinds[col][0], endOfMibView
                         nullVarBinds[col] = True
+
                     if not lexicographicMode and not initialVars[col].isPrefixOf(name):
                         varBindTable[row][col] = previousVarBinds[col][0], endOfMibView
                         nullVarBinds[col] = True
+
                 if stopFlag:
                     varBindTable = row and varBindTable[:row - 1] or []
                     break
diff --git a/pysnmp/hlapi/v3arch/asyncore/sync/ntforg.py b/pysnmp/hlapi/v3arch/asyncore/sync/ntforg.py
index 2cff18df..b26e2e4a 100644
--- a/pysnmp/hlapi/v3arch/asyncore/sync/ntforg.py
+++ b/pysnmp/hlapi/v3arch/asyncore/sync/ntforg.py
@@ -143,6 +143,7 @@ def sendNotification(snmpEngine, authData, transportTarget, contextData,
             errorStatus = cbCtx.get('errorStatus')
             errorIndex = cbCtx.get('errorIndex')
             varBinds = cbCtx.get('varBinds', [])
+
         else:
             errorIndication = errorStatus = errorIndex = None
             varBinds = []
diff --git a/pysnmp/hlapi/v3arch/asyncore/transport.py b/pysnmp/hlapi/v3arch/asyncore/transport.py
index 2cae2d7d..3e03b6af 100644
--- a/pysnmp/hlapi/v3arch/asyncore/transport.py
+++ b/pysnmp/hlapi/v3arch/asyncore/transport.py
@@ -53,11 +53,10 @@ class UdpTransportTarget(AbstractTransportTarget):
 
     def _resolveAddr(self, transportAddr):
         try:
-            return socket.getaddrinfo(transportAddr[0],
-                                      transportAddr[1],
-                                      socket.AF_INET,
-                                      socket.SOCK_DGRAM,
-                                      socket.IPPROTO_UDP)[0][4][:2]
+            return socket.getaddrinfo(
+                transportAddr[0], transportAddr[1], socket.AF_INET,
+                socket.SOCK_DGRAM, socket.IPPROTO_UDP)[0][4][:2]
+
         except socket.gaierror as exc:
             raise error.PySnmpError('Bad IPv4/UDP transport address %s: %s' % (
                 '@'.join([str(x) for x in transportAddr]), exc))
@@ -111,11 +110,10 @@ class Udp6TransportTarget(AbstractTransportTarget):
 
     def _resolveAddr(self, transportAddr):
         try:
-            return socket.getaddrinfo(transportAddr[0],
-                                      transportAddr[1],
-                                      socket.AF_INET6,
-                                      socket.SOCK_DGRAM,
-                                      socket.IPPROTO_UDP)[0][4][:2]
+            return socket.getaddrinfo(
+                transportAddr[0], transportAddr[1], socket.AF_INET6,
+                socket.SOCK_DGRAM, socket.IPPROTO_UDP)[0][4][:2]
+
         except socket.gaierror as exc:
             raise error.PySnmpError('Bad IPv6/UDP transport address %s: %s' % (
                 '@'.join([str(x) for x in transportAddr]), exc))
diff --git a/pysnmp/hlapi/v3arch/auth.py b/pysnmp/hlapi/v3arch/auth.py
index 7c232221..18b4b328 100644
--- a/pysnmp/hlapi/v3arch/auth.py
+++ b/pysnmp/hlapi/v3arch/auth.py
@@ -174,48 +174,60 @@ class CommunityData(object):
     def __init__(self, communityIndex, communityName=None, mpModel=None,
                  contextEngineId=None, contextName=None, tag=None,
                  securityName=None):
+
         if mpModel is not None:
             self.mpModel = mpModel
             self.securityModel = mpModel + 1
+
         self.contextEngineId = contextEngineId
+
         if contextName is not None:
             self.contextName = contextName
+
         if tag is not None:
             self.tag = tag
+
         # a single arg is considered as a community name
         if communityName is None:
             communityName, communityIndex = communityIndex, None
+
         self.communityName = communityName
+
         # Autogenerate communityIndex if not specified
         if communityIndex is None:
-            self.communityIndex = self.securityName = 's%s' % hash(
+            self.securityName = 's%s' % hash(
                 (self.communityName, self.mpModel, self.contextEngineId,
-                 self.contextName, self.tag)
-            )
+                 self.contextName, self.tag))
+
+            self.communityIndex = self.securityName
+
         else:
             self.communityIndex = communityIndex
-            self.securityName = securityName is not None and securityName or communityIndex
+
+            if securityName is None:
+                self.securityName = communityIndex
+
+            else:
+                self.securityName = securityName
 
     def __hash__(self):
         raise TypeError('%s is not hashable' % self.__class__.__name__)
 
     def __repr__(self):
-        return '%s(communityIndex=%r, communityName=<COMMUNITY>, mpModel=%r, contextEngineId=%r, contextName=%r, tag=%r, securityName=%r)' % (
-            self.__class__.__name__,
-            self.communityIndex,
-            self.mpModel,
-            self.contextEngineId,
-            self.contextName,
-            self.tag,
-            self.securityName
-        )
+        return ('%s(communityIndex=%r, communityName=<COMMUNITY>, mpModel=%r, '
+                'contextEngineId=%r, contextName=%r, tag=%r, securityName='
+                '%r)') % (self.__class__.__name__, self.communityIndex,
+                          self.mpModel, self.contextEngineId, self.contextName,
+                          self.tag, self.securityName)
 
     def clone(self, communityIndex=None, communityName=None,
               mpModel=None, contextEngineId=None,
               contextName=None, tag=None, securityName=None):
+
         # a single arg is considered as a community name
         if communityName is None:
             communityName, communityIndex = communityIndex, None
+
         return self.__class__(
             communityIndex,
             communityName is None and self.communityName or communityName,
@@ -223,8 +235,7 @@ class CommunityData(object):
             contextEngineId is None and self.contextEngineId or contextEngineId,
             contextName is None and self.contextName or contextName,
             tag is None and self.tag or tag,
-            securityName is None and self.securityName or securityName
-        )
+            securityName is None and self.securityName or securityName)
 
 
 class UsmUserData(object):
@@ -306,28 +317,38 @@ class UsmUserData(object):
                  authProtocol=None, privProtocol=None,
                  securityEngineId=None,
                  securityName=None):
+
         self.userName = userName
+
         if securityName is None:
             self.securityName = userName
+
         else:
             self.securityName = securityName
 
         if authKey is not None:
             self.authKey = authKey
+
             if authProtocol is None:
                 self.authProtocol = config.USM_AUTH_HMAC96_MD5
+
             else:
                 self.authProtocol = authProtocol
+
             if self.securityLevel != 'authPriv':
                 self.securityLevel = 'authNoPriv'
 
         if privKey is not None:
             self.privKey = privKey
+
             if self.authProtocol == config.USM_AUTH_NONE:
                 raise error.PySnmpError('Privacy implies authenticity')
+
             self.securityLevel = 'authPriv'
+
             if privProtocol is None:
                 self.privProtocol = config.USM_PRIV_CBC56_DES
+
             else:
                 self.privProtocol = privProtocol
 
@@ -337,19 +358,19 @@ class UsmUserData(object):
         raise TypeError('%s is not hashable' % self.__class__.__name__)
 
     def __repr__(self):
-        return '%s(userName=%r, authKey=<AUTHKEY>, privKey=<PRIVKEY>, authProtocol=%r, privProtocol=%r, securityEngineId=%r, securityName=%r)' % (
-            self.__class__.__name__,
-            self.userName,
-            self.authProtocol,
-            self.privProtocol,
+        return ('%s(userName=%r, authKey=<AUTHKEY>, privKey=<PRIVKEY>, '
+                'authProtocol=%r, privProtocol=%r, securityEngineId=%r, '
+                'securityName=%r)') % (
+            self.__class__.__name__, self.userName,
+            self.authProtocol, self.privProtocol,
             self.securityEngineId is None and '<DEFAULT>' or self.securityEngineId,
-            self.securityName
-        )
+            self.securityName)
 
     def clone(self, userName=None,
               authKey=None, privKey=None,
               authProtocol=None, privProtocol=None,
               securityEngineId=None, securityName=None):
+
         return self.__class__(
             userName is None and self.userName or userName,
             authKey is None and self.authKey or authKey,
@@ -357,5 +378,4 @@ class UsmUserData(object):
             authProtocol is None and self.authProtocol or authProtocol,
             privProtocol is None and self.privProtocol or privProtocol,
             securityEngineId is None and self.securityEngineId or securityEngineId,
-            securityName=securityName is None and self.securityName or securityName
-        )
+            securityName=securityName is None and self.securityName or securityName)
diff --git a/pysnmp/hlapi/v3arch/lcd.py b/pysnmp/hlapi/v3arch/lcd.py
index b3397b0c..0e1eb9c5 100644
--- a/pysnmp/hlapi/v3arch/lcd.py
+++ b/pysnmp/hlapi/v3arch/lcd.py
@@ -21,10 +21,13 @@ class AbstractLcdConfigurator(object):
 
     def _getCache(self, snmpEngine):
         cacheId = self.__class__.__name__
+
         cache = snmpEngine.getUserContext(cacheId)
+
         if cache is None:
             cache = dict([(x, {}) for x in self.cacheKeys])
             snmpEngine.setUserContext(**{cacheId: cache})
+
         return cache
 
     def configure(self, snmpEngine, *args, **kwargs):
@@ -37,8 +40,10 @@ class AbstractLcdConfigurator(object):
 class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
     cacheKeys = ['auth', 'parm', 'tran', 'addr']
 
-    def configure(self, snmpEngine, authData, transportTarget, contextName, **options):
+    def configure(self, snmpEngine, authData, transportTarget,
+                  contextName, **options):
         cache = self._getCache(snmpEngine)
+
         if isinstance(authData, CommunityData):
             if authData.communityIndex not in cache['auth']:
                 config.addV1System(
@@ -50,9 +55,12 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
                     authData.tag,
                     authData.securityName
                 )
+
                 cache['auth'][authData.communityIndex] = authData
+
         elif isinstance(authData, UsmUserData):
             authDataKey = authData.userName, authData.securityEngineId
+
             if authDataKey not in cache['auth']:
                 config.addV3User(
                     snmpEngine,
@@ -62,37 +70,48 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
                     authData.securityEngineId,
                     securityName=authData.securityName
                 )
+
                 cache['auth'][authDataKey] = authData
+
         else:
             raise error.PySnmpError('Unsupported authentication object')
 
         paramsKey = (authData.securityName,
                      authData.securityLevel,
                      authData.mpModel)
+
         if paramsKey in cache['parm']:
             paramsName, useCount = cache['parm'][paramsKey]
+
             cache['parm'][paramsKey] = paramsName, useCount + 1
+
         else:
             paramsName = 'p%s' % self.nextID()
             config.addTargetParams(
                 snmpEngine, paramsName,
                 authData.securityName, authData.securityLevel, authData.mpModel
             )
+
             cache['parm'][paramsKey] = paramsName, 1
 
         if transportTarget.TRANSPORT_DOMAIN in cache['tran']:
             transport, useCount = cache['tran'][transportTarget.TRANSPORT_DOMAIN]
             transportTarget.verifyDispatcherCompatibility(snmpEngine)
+
             cache['tran'][transportTarget.TRANSPORT_DOMAIN] = transport, useCount + 1
+
         elif config.getTransport(snmpEngine, transportTarget.TRANSPORT_DOMAIN):
             transportTarget.verifyDispatcherCompatibility(snmpEngine)
+
         else:
             transport = transportTarget.openClientMode()
+
             config.addTransport(
                 snmpEngine,
                 transportTarget.TRANSPORT_DOMAIN,
                 transport
             )
+
             cache['tran'][transportTarget.TRANSPORT_DOMAIN] = transport, 1
 
         transportKey = (paramsName, transportTarget.TRANSPORT_DOMAIN,
@@ -105,8 +124,10 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
         if transportKey in cache['addr']:
             addrName, useCount = cache['addr'][transportKey]
             cache['addr'][transportKey] = addrName, useCount + 1
+
         else:
             addrName = 'a%s' % self.nextID()
+
             config.addTargetAddr(
                 snmpEngine, addrName,
                 transportTarget.TRANSPORT_DOMAIN,
@@ -116,23 +137,30 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
                 transportTarget.retries,
                 transportTarget.tagList
             )
+
             cache['addr'][transportKey] = addrName, 1
 
         return addrName, paramsName
 
     def unconfigure(self, snmpEngine, authData=None, contextName=null, **options):
         cache = self._getCache(snmpEngine)
+
         if authData:
             if isinstance(authData, CommunityData):
                 authDataKey = authData.communityIndex
+
             elif isinstance(authData, UsmUserData):
                 authDataKey = authData.userName, authData.securityEngineId
+
             else:
                 raise error.PySnmpError('Unsupported authentication object')
+
             if authDataKey in cache['auth']:
                 authDataKeys = (authDataKey,)
+
             else:
                 raise error.PySnmpError('Unknown authData %s' % (authData,))
+
         else:
             authDataKeys = list(cache['auth'].keys())
 
@@ -140,35 +168,44 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
 
         for authDataKey in authDataKeys:
             authDataX = cache['auth'][authDataKey]
+
             del cache['auth'][authDataKey]
+
             if isinstance(authDataX, CommunityData):
                 config.delV1System(
                     snmpEngine,
                     authDataX.communityIndex
                 )
+
             elif isinstance(authDataX, UsmUserData):
                 config.delV3User(
                     snmpEngine,
                     authDataX.userName,
                     authDataX.securityEngineId
                 )
+
             else:
                 raise error.PySnmpError('Unsupported authentication object')
 
             paramsKey = (authDataX.securityName,
                          authDataX.securityLevel,
                          authDataX.mpModel)
+
             if paramsKey in cache['parm']:
                 paramsName, useCount = cache['parm'][paramsKey]
+
                 useCount -= 1
+
                 if useCount:
                     cache['parm'][paramsKey] = paramsName, useCount
+
                 else:
                     del cache['parm'][paramsKey]
-                    config.delTargetParams(
-                        snmpEngine, paramsName
-                    )
+
+                    config.delTargetParams(snmpEngine, paramsName)
+
                     paramsNames.add(paramsName)
+
             else:
                 raise error.PySnmpError('Unknown target %s' % (paramsKey,))
 
@@ -176,22 +213,30 @@ class CommandGeneratorLcdConfigurator(AbstractLcdConfigurator):
 
             for addrKey in addrKeys:
                 addrName, useCount = cache['addr'][addrKey]
+
                 useCount -= 1
+
                 if useCount:
                     cache['addr'][addrKey] = addrName, useCount
+
                 else:
                     config.delTargetAddr(snmpEngine, addrName)
+
                     del cache['addr'][addrKey]
+
                     addrNames.add(addrKey)
 
                     if addrKey[1] in cache['tran']:
                         transport, useCount = cache['tran'][addrKey[1]]
+
                         if useCount > 1:
                             useCount -= 1
                             cache['tran'][addrKey[1]] = transport, useCount
+
                         else:
                             config.delTransport(snmpEngine, addrKey[1])
                             transport.closeTransport()
+
                             del cache['tran'][addrKey[1]]
 
         return addrNames, paramsNames
@@ -204,6 +249,7 @@ class NotificationOriginatorLcdConfigurator(AbstractLcdConfigurator):
     def configure(self, snmpEngine, authData, transportTarget, notifyType,
                   contextName, **options):
         cache = self._getCache(snmpEngine)
+
         notifyName = None
 
         # Create matching transport tags if not given by user. Not good!
@@ -211,79 +257,97 @@ class NotificationOriginatorLcdConfigurator(AbstractLcdConfigurator):
             transportTarget.tagList = str(
                 hash((authData.securityName, transportTarget.transportAddr))
             )
+
         if isinstance(authData, CommunityData) and not authData.tag:
             authData.tag = transportTarget.tagList.split()[0]
 
         addrName, paramsName = self._cmdGenLcdCfg.configure(
             snmpEngine, authData, transportTarget, contextName, **options)
+
         tagList = transportTarget.tagList.split()
+
         if not tagList:
             tagList = ['']
+
         for tag in tagList:
             notifyNameKey = paramsName, tag, notifyType
+
             if notifyNameKey in cache['name']:
                 notifyName, paramsName, useCount = cache['name'][notifyNameKey]
+
                 cache['name'][notifyNameKey] = notifyName, paramsName, useCount + 1
+
             else:
                 notifyName = 'n%s' % self.nextID()
+
                 config.addNotificationTarget(
-                    snmpEngine,
-                    notifyName,
-                    paramsName,
-                    tag,
-                    notifyType
-                )
+                    snmpEngine, notifyName, paramsName, tag, notifyType)
+
                 cache['name'][notifyNameKey] = notifyName, paramsName, 1
+
         authDataKey = authData.securityName, authData.securityModel, authData.securityLevel, contextName
+
         if authDataKey in cache['auth']:
             authDataX, subTree, useCount = cache['auth'][authDataKey]
+
             cache['auth'][authDataKey] = authDataX, subTree, useCount + 1
+
         else:
             subTree = (1, 3, 6)
-            config.addVacmUser(snmpEngine,
-                               authData.securityModel,
-                               authData.securityName,
-                               authData.securityLevel,
-                               (), (), subTree, contextName=contextName)
+
+            config.addVacmUser(
+                snmpEngine,authData.securityModel, authData.securityName,
+                authData.securityLevel, (), (), subTree,
+                contextName=contextName)
+
             cache['auth'][authDataKey] = authData, subTree, 1
 
         return notifyName
 
     def unconfigure(self, snmpEngine, authData=None, contextName=null, **options):
         cache = self._getCache(snmpEngine)
+
         if authData:
             authDataKey = authData.securityName, authData.securityModel, authData.securityLevel, contextName
+
             if authDataKey in cache['auth']:
                 authDataKeys = (authDataKey,)
+
             else:
                 raise error.PySnmpError('Unknown authData %s' % (authData,))
+
         else:
             authDataKeys = tuple(cache['auth'])
 
         addrNames, paramsNames = self._cmdGenLcdCfg.unconfigure(
             snmpEngine, authData, contextName, **options)
 
-        notifyAndParamsNames = [(cache['name'][x], x) for x in cache['name'].keys() if x[0] in paramsNames]
+        notifyAndParamsNames = [
+            (cache['name'][x], x) for x in cache['name'].keys()
+            if x[0] in paramsNames
+        ]
 
         for (notifyName, paramsName, useCount), notifyNameKey in notifyAndParamsNames:
             useCount -= 1
+
             if useCount:
                 cache['name'][notifyNameKey] = notifyName, paramsName, useCount
+
             else:
-                config.delNotificationTarget(
-                    snmpEngine, notifyName, paramsName
-                )
+                config.delNotificationTarget(snmpEngine, notifyName, paramsName)
                 del cache['name'][notifyNameKey]
 
         for authDataKey in authDataKeys:
             authDataX, subTree, useCount = cache['auth'][authDataKey]
+
             useCount -= 1
+
             if useCount:
                 cache['auth'][authDataKey] = authDataX, subTree, useCount
+
             else:
                 config.delTrapUser(
-                    snmpEngine, authDataX.securityModel,
-                    authDataX.securityName, authDataX.securityLevel,
-                    subTree
-                )
+                    snmpEngine, authDataX.securityModel, authDataX.securityName,
+                    authDataX.securityLevel, subTree)
+
                 del cache['auth'][authDataKey]
diff --git a/pysnmp/hlapi/v3arch/twisted/cmdgen.py b/pysnmp/hlapi/v3arch/twisted/cmdgen.py
index 91cfdab2..528c92df 100644
--- a/pysnmp/hlapi/v3arch/twisted/cmdgen.py
+++ b/pysnmp/hlapi/v3arch/twisted/cmdgen.py
@@ -110,38 +110,41 @@ def getCmd(snmpEngine, authData, transportTarget, contextData,
     ...
     >>> react(run)
     (0, 0, [ObjectType(ObjectIdentity(ObjectName('1.3.6.1.2.1.1.1.0')), DisplayString('SunOS zeus.snmplabs.com 4.1.3_U1 1 sun4m'))])
-    >>>
-
     """
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
+
         lookupMib, deferred = cbCtx
+
         if errorIndication:
             deferred.errback(Failure(errorIndication))
+
         else:
             try:
-                varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds, lookupMib)
+                varBinds = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds, lookupMib)
 
             except Exception as e:
                 deferred.errback(Failure(e))
 
             else:
-                deferred.callback((errorStatus, errorIndex, varBindsUnmade))
+                deferred.callback((errorStatus, errorIndex, varBinds))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     deferred = Deferred()
 
     cmdgen.GetCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
-        contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
-        (options.get('lookupMib', True), deferred)
-    )
+        contextData.contextName, varBinds, __cbFun,
+        (options.get('lookupMib', True), deferred))
+
     return deferred
 
+
 def setCmd(snmpEngine, authData, transportTarget, contextData,
            *varBinds, **options):
     """Performs SNMP SET query.
@@ -227,38 +230,41 @@ def setCmd(snmpEngine, authData, transportTarget, contextData,
     ...
     >>> react(run)
     (0, 0, [ObjectType(ObjectIdentity(ObjectName('1.3.6.1.2.1.1.1.0')), DisplayString('Linux i386'))])
-    >>>
-
     """
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
+
         lookupMib, deferred = cbCtx
+
         if errorIndication:
             deferred.errback(Failure(errorIndication))
+
         else:
             try:
-                varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds, lookupMib)
+                varBinds = VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache, varBinds, lookupMib)
 
             except Exception as e:
                 deferred.errback(Failure(e))
 
             else:
-                deferred.callback((errorStatus, errorIndex, varBindsUnmade))
+                deferred.callback((errorStatus, errorIndex, varBinds))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     deferred = Deferred()
 
     cmdgen.SetCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
-        contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
-        (options.get('lookupMib', True), deferred)
-    )
+        contextData.contextName, varBinds, __cbFun,
+        (options.get('lookupMib', True), deferred))
+
     return deferred
 
+
 def nextCmd(snmpEngine, authData, transportTarget, contextData,
             *varBinds, **options):
     """Performs SNMP GETNEXT query.
@@ -352,44 +358,49 @@ def nextCmd(snmpEngine, authData, transportTarget, contextData,
     ...
     >>> react(run)
     (0, 0, [[ObjectType(ObjectIdentity(ObjectName('1.3.6.1.2.1.1.1.0')), DisplayString('SunOS zeus.snmplabs.com 4.1.3_U1 1 sun4m'))]])
-    >>>
-
     """
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBindTable, cbCtx):
+
         lookupMib, deferred = cbCtx
-        if (options.get('ignoreNonIncreasingOid', False) and
-                errorIndication and isinstance(errorIndication, errind.OidNotIncreasing)):
+
+        if (options.get('ignoreNonIncreasingOid', False) and errorIndication
+                and isinstance(errorIndication, errind.OidNotIncreasing)):
             errorIndication = None
+
         if errorIndication:
             deferred.errback(Failure(errorIndication))
+
         else:
             try:
-                varBindsUnmade = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
-                                                              varBindTableRow,
-                                                              lookupMib)
-                                  for varBindTableRow in varBindTable]
+                varBindTable = [
+                    VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
+                                                varBindTableRow, lookupMib)
+                    for varBindTableRow in varBindTable
+                ]
 
             except Exception as e:
                 deferred.errback(Failure(e))
 
             else:
-                deferred.callback((errorStatus, errorIndex, varBindsUnmade))
+                deferred.callback((errorStatus, errorIndex, varBindTable))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     deferred = Deferred()
 
     cmdgen.NextCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
-        contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds), __cbFun,
-        (options.get('lookupMib', True), deferred)
-    )
+        contextData.contextName, varBinds, __cbFun,
+        (options.get('lookupMib', True), deferred))
+
     return deferred
 
+
 def bulkCmd(snmpEngine, authData, transportTarget, contextData,
             nonRepeaters, maxRepetitions, *varBinds, **options):
     """Performs SNMP GETBULK query.
@@ -511,41 +522,45 @@ def bulkCmd(snmpEngine, authData, transportTarget, contextData,
     ...
     >>> react(run)
     (0, 0, [[ObjectType(ObjectIdentity(ObjectName('1.3.6.1.2.1.1.1.0')), DisplayString('SunOS zeus.snmplabs.com 4.1.3_U1 1 sun4m'))], [ObjectType(ObjectIdentity(ObjectName('1.3.6.1.2.1.1.2.0')), ObjectIdentifier('1.3.6.1.4.1.424242.1.1'))]])
-    >>>
-
     """
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBindTable, cbCtx):
+
         lookupMib, deferred = cbCtx
-        if options.get('ignoreNonIncreasingOid', False) and errorIndication and \
-                isinstance(errorIndication, errind.OidNotIncreasing):
+
+        if (options.get('ignoreNonIncreasingOid', False) and errorIndication
+                and isinstance(errorIndication, errind.OidNotIncreasing)):
             errorIndication = None
+
         if errorIndication:
             deferred.errback(Failure(errorIndication))
+
         else:
             try:
-                varBindsUnmade = [VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
-                                                              varBindTableRow,
-                                                              lookupMib)
-                                  for varBindTableRow in varBindTable]
+                varBindTable = [
+                    VB_PROCESSOR.unmakeVarBinds(snmpEngine.cache,
+                                                varBindTableRow, lookupMib)
+                    for varBindTableRow in varBindTable
+                ]
 
             except Exception as e:
                 deferred.errback(Failure(e))
 
             else:
-                deferred.callback((errorStatus, errorIndex, varBindsUnmade))
+                deferred.callback((errorStatus, errorIndex, varBindTable))
 
     addrName, paramsName = LCD.configure(
         snmpEngine, authData, transportTarget, contextData.contextName)
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     deferred = Deferred()
 
     cmdgen.BulkCommandGenerator().sendVarBinds(
         snmpEngine, addrName, contextData.contextEngineId,
         contextData.contextName, nonRepeaters, maxRepetitions,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds),
-        __cbFun,
-        (options.get('lookupMib', True), deferred)
-    )
+        varBinds, __cbFun, (options.get('lookupMib', True),
+                            deferred))
+
     return deferred
diff --git a/pysnmp/hlapi/v3arch/twisted/ntforg.py b/pysnmp/hlapi/v3arch/twisted/ntforg.py
index 5243c66f..3ea2aa59 100644
--- a/pysnmp/hlapi/v3arch/twisted/ntforg.py
+++ b/pysnmp/hlapi/v3arch/twisted/ntforg.py
@@ -21,6 +21,7 @@ __all__ = ['sendNotification']
 VB_PROCESSOR = NotificationOriginatorVarBinds()
 LCD = NotificationOriginatorLcdConfigurator()
 
+
 def sendNotification(snmpEngine, authData, transportTarget, contextData,
                      notifyType, *varBinds, **options):
     """Sends SNMP notification.
@@ -145,27 +146,26 @@ def sendNotification(snmpEngine, authData, transportTarget, contextData,
     ...
     >>> react(run)
     (0, 0, [])
-    >>>
-
     """
     def __cbFun(snmpEngine, sendRequestHandle,
                 errorIndication, errorStatus, errorIndex,
                 varBinds, cbCtx):
+
         lookupMib, deferred = cbCtx
 
         if errorIndication:
             deferred.errback(Failure(errorIndication))
+
         else:
             try:
-                varBindsUnmade = VB_PROCESSOR.unmakeVarBinds(
-                    snmpEngine.cache, varBinds, lookupMib
-                )
+                varBinds = VB_PROCESSOR.unmakeVarBinds(
+                    snmpEngine.cache, varBinds, lookupMib)
 
             except Exception as e:
                 deferred.errback(Failure(e))
 
             else:
-                deferred.callback((errorStatus, errorIndex, varBindsUnmade))
+                deferred.callback((errorStatus, errorIndex, varBinds))
 
     notifyName = LCD.configure(snmpEngine, authData, transportTarget,
                                notifyType, contextData.contextName)
@@ -173,15 +173,13 @@ def sendNotification(snmpEngine, authData, transportTarget, contextData,
     def __trapFun(deferred):
         deferred.callback((0, 0, []))
 
+    varBinds = VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds)
+
     deferred = Deferred()
 
     ntforg.NotificationOriginator().sendVarBinds(
-        snmpEngine,
-        notifyName,
-        contextData.contextEngineId,
-        contextData.contextName,
-        VB_PROCESSOR.makeVarBinds(snmpEngine.cache, varBinds),
-        __cbFun,
+        snmpEngine, notifyName, contextData.contextEngineId,
+        contextData.contextName, varBinds, __cbFun,
         (options.get('lookupMib', True), deferred)
     )
 
diff --git a/pysnmp/hlapi/v3arch/twisted/transport.py b/pysnmp/hlapi/v3arch/twisted/transport.py
index 11119fc4..71b0337a 100644
--- a/pysnmp/hlapi/v3arch/twisted/transport.py
+++ b/pysnmp/hlapi/v3arch/twisted/transport.py
@@ -12,6 +12,7 @@ from pysnmp.hlapi.transport import AbstractTransportTarget
 
 __all__ = ['UdpTransportTarget']
 
+
 class UdpTransportTarget(AbstractTransportTarget):
     """Creates UDP/IPv4 configuration entry and initialize socket API if needed.
 
@@ -43,18 +44,17 @@ class UdpTransportTarget(AbstractTransportTarget):
     >>> from pysnmp.hlapi.twisted import UdpTransportTarget
     >>> UdpTransportTarget(('demo.snmplabs.com', 161))
     UdpTransportTarget(('195.218.195.228', 161), timeout=1, retries=5, tagList='')
-    >>>
-
     """
     TRANSPORT_DOMAIN = udp.DOMAIN_NAME
     PROTO_TRANSPORT = udp.UdpTwistedTransport
 
     def _resolveAddr(self, transportAddr):
         try:
-            return socket.getaddrinfo(transportAddr[0],
-                                      transportAddr[1],
-                                      socket.AF_INET,
-                                      socket.SOCK_DGRAM,
-                                      socket.IPPROTO_UDP)[0][4][:2]
+            return socket.getaddrinfo(
+                transportAddr[0], transportAddr[1], socket.AF_INET,
+                socket.SOCK_DGRAM, socket.IPPROTO_UDP)[0][4][:2]
+
         except socket.gaierror as exc:
-            raise PySnmpError('Bad IPv4/UDP transport address %s: %s' % ('@'.join([str(x) for x in transportAddr]), exc))
+            raise PySnmpError(
+                'Bad IPv4/UDP transport address %s: '
+                '%s' % ('@'.join(str(x) for x in transportAddr), exc))
diff --git a/pysnmp/hlapi/varbinds.py b/pysnmp/hlapi/varbinds.py
index d3742a75..0eed7e50 100644
--- a/pysnmp/hlapi/varbinds.py
+++ b/pysnmp/hlapi/varbinds.py
@@ -38,7 +38,9 @@ class CommandGeneratorVarBinds(MibViewControllerManager):
                 varBind = ObjectType(*varBind)
 
             elif isinstance(varBind[0][0], tuple):  # legacy
-                varBind = ObjectType(ObjectIdentity(varBind[0][0][0], varBind[0][0][1], *varBind[0][1:]), varBind[1])
+                varBind = ObjectType(
+                    ObjectIdentity(varBind[0][0][0], varBind[0][0][1],
+                                   *varBind[0][1:]), varBind[1])
 
             else:
                 varBind = ObjectType(ObjectIdentity(varBind[0]), varBind[1])
@@ -50,7 +52,10 @@ class CommandGeneratorVarBinds(MibViewControllerManager):
     def unmakeVarBinds(self, userCache, varBinds, lookupMib=True):
         if lookupMib:
             mibViewController = self.getMibViewController(userCache)
-            varBinds = [ObjectType(ObjectIdentity(x[0]), x[1]).resolveWithMib(mibViewController) for x in varBinds]
+            varBinds = [
+                ObjectType(ObjectIdentity(x[0]),
+                           x[1]).resolveWithMib(mibViewController)
+                for x in varBinds]
 
         return varBinds
 
@@ -85,5 +90,9 @@ class NotificationOriginatorVarBinds(MibViewControllerManager):
     def unmakeVarBinds(self, userCache, varBinds, lookupMib=False):
         if lookupMib:
             mibViewController = self.getMibViewController(userCache)
-            varBinds = [ObjectType(ObjectIdentity(x[0]), x[1]).resolveWithMib(mibViewController) for x in varBinds]
+            varBinds = [
+                ObjectType(ObjectIdentity(x[0]),
+                           x[1]).resolveWithMib(mibViewController)
+                for x in varBinds]
+
         return varBinds
diff --git a/pysnmp/nextid.py b/pysnmp/nextid.py
index f81bc9b6..60a61a11 100644
--- a/pysnmp/nextid.py
+++ b/pysnmp/nextid.py
@@ -13,30 +13,33 @@ class Integer(object):
     """Return a next value in a reasonably MT-safe manner"""
 
     def __init__(self, maximum, increment=256):
-        self.__maximum = maximum
+        self._maximum = maximum
         if increment >= maximum:
             increment = maximum
-        self.__increment = increment
-        self.__threshold = increment // 2
-        e = random.randrange(self.__maximum - self.__increment)
-        self.__bank = list(range(e, e + self.__increment))
+
+        self._increment = increment
+        self._threshold = increment // 2
+
+        e = random.randrange(self._maximum - self._increment)
+
+        self._bank = list(range(e, e + self._increment))
 
     def __repr__(self):
         return '%s(%d, %d)' % (
-            self.__class__.__name__,
-            self.__maximum,
-            self.__increment
-        )
+            self.__class__.__name__, self._maximum, self._increment)
 
     def __call__(self):
-        v = self.__bank.pop(0)
-        if v % self.__threshold:
-            return v
-        else:
-            # this is MT-safe unless too many (~ increment/2) threads
-            # bump into this code simultaneously
-            e = self.__bank[-1] + 1
-            if e > self.__maximum:
-                e = 0
-            self.__bank.extend(range(e, e + self.__threshold))
+        v = self._bank.pop(0)
+
+        if v % self._threshold:
             return v
+
+        # Should be MT-safe unless too many (~ increment/2) threads
+        # bump into this code simultaneously
+        e = self._bank[-1] + 1
+        if e > self._maximum:
+            e = 0
+
+        self._bank.extend(range(e, e + self._threshold))
+
+        return v
diff --git a/pysnmp/proto/acmod/rfc3415.py b/pysnmp/proto/acmod/rfc3415.py
index fb4c4adf..13d9de12 100644
--- a/pysnmp/proto/acmod/rfc3415.py
+++ b/pysnmp/proto/acmod/rfc3415.py
@@ -17,65 +17,63 @@ class Vacm(object):
 
     _powOfTwoSeq = (128, 64, 32, 16, 8, 4, 2, 1)
 
-    def isAccessAllowed(self,
-                        snmpEngine,
-                        securityModel,
-                        securityName,
-                        securityLevel,
-                        viewType,
-                        contextName,
-                        variableName):
+    def isAccessAllowed(self, snmpEngine, securityModel, securityName,
+                        securityLevel, viewType, contextName, variableName):
+
         mibInstrumController = snmpEngine.msgAndPduDsp.mibInstrumController
+        mibBuilder = mibInstrumController.mibBuilder
 
         debug.logger & debug.FLAG_ACL and debug.logger(
-            'isAccessAllowed: securityModel %s, securityName %s, securityLevel %s, viewType %s, contextName %s for variableName %s' % (
-                securityModel, securityName, securityLevel, viewType, contextName, variableName))
+            'isAccessAllowed: securityModel %s, securityName %s, '
+            'securityLevel %s, viewType %s, contextName %s for '
+            'variableName %s' % (securityModel, securityName, securityLevel,
+                                 viewType, contextName, variableName))
 
         # 3.2.1
-        vacmContextEntry, = mibInstrumController.mibBuilder.importSymbols(
+        vacmContextEntry, = mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
 
         tblIdx = vacmContextEntry.getInstIdFromIndices(contextName)
+
         try:
             vacmContextEntry.getNode(
-                vacmContextEntry.name + (1,) + tblIdx
-            ).syntax
+                vacmContextEntry.name + (1,) + tblIdx).syntax
 
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noSuchContext)
 
         # 3.2.2
-        vacmSecurityToGroupEntry, = mibInstrumController.mibBuilder.importSymbols(
+        vacmSecurityToGroupEntry, = mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmSecurityToGroupEntry')
+
         tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(
-            securityModel, securityName
-        )
+            securityModel, securityName)
 
         try:
             vacmGroupName = vacmSecurityToGroupEntry.getNode(
-                vacmSecurityToGroupEntry.name + (3,) + tblIdx
-            ).syntax
+                vacmSecurityToGroupEntry.name + (3,) + tblIdx).syntax
 
         except NoSuchInstanceError:
             raise error.StatusInformation(errorIndication=errind.noGroupName)
 
         # 3.2.3
-        vacmAccessEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry'
-        )
+        vacmAccessEntry, = mibBuilder.importSymbols(
+            'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry')
 
         # XXX partial context name match
         tblIdx = vacmAccessEntry.getInstIdFromIndices(
-            vacmGroupName, contextName, securityModel, securityLevel
-        )
+            vacmGroupName, contextName, securityModel, securityLevel)
 
         # 3.2.4
         if viewType == 'read':
             entryIdx = vacmAccessEntry.name + (5,) + tblIdx
+
         elif viewType == 'write':
             entryIdx = vacmAccessEntry.name + (6,) + tblIdx
+
         elif viewType == 'notify':
             entryIdx = vacmAccessEntry.name + (7,) + tblIdx
+
         else:
             raise error.ProtocolError('Unknown view type %s' % viewType)
 
@@ -93,19 +91,20 @@ class Vacm(object):
         # 3.2.5a
         vacmViewTreeFamilyEntry, = mibInstrumController.mibBuilder.importSymbols(
             'SNMP-VIEW-BASED-ACM-MIB', 'vacmViewTreeFamilyEntry')
+
         tblIdx = vacmViewTreeFamilyEntry.getInstIdFromIndices(viewName)
 
         # Walk over entries
         initialTreeName = treeName = vacmViewTreeFamilyEntry.name + (2,) + tblIdx
+
         maskName = vacmViewTreeFamilyEntry.name + (3,) + tblIdx
 
         while True:
             vacmViewTreeFamilySubtree = vacmViewTreeFamilyEntry.getNextNode(
-                treeName
-            )
+                treeName)
+
             vacmViewTreeFamilyMask = vacmViewTreeFamilyEntry.getNextNode(
-                maskName
-            )
+                maskName)
 
             treeName = vacmViewTreeFamilySubtree.name
             maskName = vacmViewTreeFamilyMask.name
@@ -125,10 +124,12 @@ class Vacm(object):
 
                 m = len(mask) - 1
                 idx = l - 1
+
                 while idx:
                     if (idx > m or mask[idx] and
                             vacmViewTreeFamilySubtree.syntax[idx] != variableName[idx]):
                         break
+
                     idx -= 1
 
                 if idx:
diff --git a/pysnmp/proto/acmod/void.py b/pysnmp/proto/acmod/void.py
index 2f8c4e97..e3ee848f 100644
--- a/pysnmp/proto/acmod/void.py
+++ b/pysnmp/proto/acmod/void.py
@@ -15,17 +15,11 @@ class Vacm(object):
     """Void Access Control Model"""
     ACCESS_MODEL_ID = 0
 
-    def isAccessAllowed(self,
-                        snmpEngine,
-                        securityModel,
-                        securityName,
-                        securityLevel,
-                        viewType,
-                        contextName,
-                        variableName):
+    def isAccessAllowed(self, snmpEngine, securityModel, securityName,
+                        securityLevel, viewType, contextName, variableName):
         debug.logger & debug.FLAG_ACL and debug.logger(
-            'isAccessAllowed: viewType %s for variableName %s - OK' % (viewType, variableName)
-        )
+            'isAccessAllowed: viewType %s for variableName '
+            '%s - OK' % (viewType, variableName))
 
         # rfc3415 3.2.5c
         return error.StatusInformation(errorIndication=errind.accessAllowed)
diff --git a/pysnmp/proto/api/v1.py b/pysnmp/proto/api/v1.py
index 827a6a0d..f13920e7 100644
--- a/pysnmp/proto/api/v1.py
+++ b/pysnmp/proto/api/v1.py
@@ -39,10 +39,18 @@ class VarBindAPI(object):
     @staticmethod
     def setOIDVal(varBind, oidVal):
         oid, val = oidVal[0], oidVal[1]
+
         varBind.setComponentByPosition(0, oid)
+
         if val is None:
             val = null
-        varBind.setComponentByPosition(1).getComponentByPosition(1).setComponentByType(val.getTagSet(), val, verifyConstraints=False, matchTags=False, matchConstraints=False, innerFlag=True)
+
+        (varBind.setComponentByPosition(1)
+         .getComponentByPosition(1)
+         .setComponentByType(val.getTagSet(), val,
+                             verifyConstraints=False, matchTags=False,
+                             matchConstraints=False, innerFlag=True))
+
         return varBind
 
     @staticmethod
@@ -61,14 +69,17 @@ class PDUAPI(object):
 
     def setDefaults(self, pdu):
         pdu.setComponentByPosition(
-            0, getNextRequestID(), verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, getNextRequestID(), verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            1, self._errorStatus, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, self._errorStatus, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            2, self._errorIndex, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._errorIndex, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(3)
 
     @staticmethod
@@ -90,12 +101,14 @@ class PDUAPI(object):
     @staticmethod
     def getErrorIndex(pdu, muteErrors=False):
         errorIndex = pdu.getComponentByPosition(2)
+
         if errorIndex > len(pdu[3]):
             if muteErrors:
                 return errorIndex.clone(len(pdu[3]))
+
             raise error.ProtocolError(
-                'Error index out of range: %s > %s' % (errorIndex, len(pdu[3]))
-            )
+                'Error index out of range: %s > %s' % (errorIndex, len(pdu[3])))
+
         return errorIndex
 
     @staticmethod
@@ -119,20 +132,23 @@ class PDUAPI(object):
 
     @staticmethod
     def getVarBinds(pdu):
-        return [apiVarBind.getOIDVal(varBind) for varBind in pdu.getComponentByPosition(3)]
+        return [apiVarBind.getOIDVal(varBind)
+                for varBind in pdu.getComponentByPosition(3)]
 
     @staticmethod
     def setVarBinds(pdu, varBinds):
         varBindList = pdu.setComponentByPosition(3).getComponentByPosition(3)
+
         varBindList.clear()
+
         for idx, varBind in enumerate(varBinds):
             if isinstance(varBind, VarBind):
                 varBindList.setComponentByPosition(idx, varBind)
+
             else:
                 varBindList.setComponentByPosition(idx)
                 apiVarBind.setOIDVal(
-                    varBindList.getComponentByPosition(idx), varBind
-                )
+                    varBindList.getComponentByPosition(idx), varBind)
 
     def getResponse(self, reqPDU):
         rspPDU = GetResponsePDU()
@@ -143,8 +159,10 @@ class PDUAPI(object):
     def getVarBindTable(self, reqPDU, rspPDU):
         if apiPDU.getErrorStatus(rspPDU) == 2:
             varBindRow = [(vb[0], null) for vb in apiPDU.getVarBinds(reqPDU)]
+
         else:
             varBindRow = apiPDU.getVarBinds(rspPDU)
+
         return [varBindRow]
 
     def getNextVarBinds(self, varBinds, errorIndex=None):
@@ -173,14 +191,32 @@ class TrapPDUAPI(object):
             try:
                 import socket
                 agentAddress = IpAddress(socket.gethostbyname(socket.gethostname()))
+
             except Exception:
                 agentAddress = IpAddress('0.0.0.0')
+
             self._networkAddress = NetworkAddress().setComponentByPosition(0, agentAddress)
-        pdu.setComponentByPosition(0, self._entOid, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(1, self._networkAddress, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(2, self._genericTrap, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(3, self._zeroInt, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        pdu.setComponentByPosition(4, self._zeroTime, verifyConstraints=False, matchTags=False, matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            0, self._entOid, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            1, self._networkAddress, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            2, self._genericTrap, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            3, self._zeroInt, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        pdu.setComponentByPosition(
+            4, self._zeroTime, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(5)
 
     @staticmethod
@@ -197,7 +233,9 @@ class TrapPDUAPI(object):
 
     @staticmethod
     def setAgentAddr(pdu, value):
-        pdu.setComponentByPosition(1).getComponentByPosition(1).setComponentByPosition(0, value)
+        (pdu.setComponentByPosition(1)
+         .getComponentByPosition(1)
+         .setComponentByPosition(0, value))
 
     @staticmethod
     def getGenericTrap(pdu):
@@ -233,24 +271,28 @@ class TrapPDUAPI(object):
 
     @staticmethod
     def getVarBinds(pdu):
-        varBinds = []
-        for varBind in pdu.getComponentByPosition(5):
-            varBinds.append(apiVarBind.getOIDVal(varBind))
-        return varBinds
+        return [apiVarBind.getOIDVal(varBind)
+                for varBind in pdu.getComponentByPosition(5)]
 
     @staticmethod
     def setVarBinds(pdu, varBinds):
         varBindList = pdu.setComponentByPosition(5).getComponentByPosition(5)
+
         varBindList.clear()
+
         idx = 0
+
         for varBind in varBinds:
             if isinstance(varBind, VarBind):
                 varBindList.setComponentByPosition(idx, varBind)
+
             else:
                 varBindList.setComponentByPosition(idx)
+
                 apiVarBind.setOIDVal(
                     varBindList.getComponentByPosition(idx), varBind
                 )
+
             idx += 1
 
 
@@ -262,8 +304,14 @@ class MessageAPI(object):
     _community = univ.OctetString('public')
 
     def setDefaults(self, msg):
-        msg.setComponentByPosition(0, self._version, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        msg.setComponentByPosition(1, self._community, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        msg.setComponentByPosition(
+            0, self._version, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        msg.setComponentByPosition(
+            1, self._community, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         return msg
 
     @staticmethod
@@ -288,14 +336,20 @@ class MessageAPI(object):
 
     @staticmethod
     def setPDU(msg, value):
-        msg.setComponentByPosition(2).getComponentByPosition(2).setComponentByType(value.getTagSet(), value, verifyConstraints=False, matchTags=False, matchConstraints=False, innerFlag=True)
+        (msg.setComponentByPosition(2)
+         .getComponentByPosition(2)
+         .setComponentByType(value.getTagSet(), value, verifyConstraints=False,
+                             matchTags=False, matchConstraints=False,
+                             innerFlag=True))
 
     def getResponse(self, reqMsg):
         rspMsg = Message()
+
         self.setDefaults(rspMsg)
         self.setVersion(rspMsg, self.getVersion(reqMsg))
         self.setCommunity(rspMsg, self.getCommunity(reqMsg))
         self.setPDU(rspMsg, apiPDU.getResponse(self.getPDU(reqMsg)))
+
         return rspMsg
 
 
diff --git a/pysnmp/proto/api/v2c.py b/pysnmp/proto/api/v2c.py
index 05de2da1..c415ca9a 100644
--- a/pysnmp/proto/api/v2c.py
+++ b/pysnmp/proto/api/v2c.py
@@ -53,7 +53,8 @@ apiVarBind = v1.apiVarBind
 
 class PDUAPI(v1.PDUAPI):
     _errorStatus = rfc1905.errorStatus.clone(0)
-    _errorIndex = univ.Integer(0).subtype(subtypeSpec=constraint.ValueRangeConstraint(0, rfc1905.max_bindings))
+    _errorIndex = univ.Integer(0).subtype(
+        subtypeSpec=constraint.ValueRangeConstraint(0, rfc1905.max_bindings))
 
     def getResponse(self, reqPDU):
         rspPDU = ResponsePDU()
@@ -86,14 +87,14 @@ class PDUAPI(v1.PDUAPI):
     def setEndOfMibError(self, pdu, errorIndex):
         varBindList = self.getVarBindList(pdu)
         varBindList[errorIndex - 1].setComponentByPosition(
-            1, rfc1905.endOfMibView, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, rfc1905.endOfMibView, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
     def setNoSuchInstanceError(self, pdu, errorIndex):
         varBindList = self.getVarBindList(pdu)
         varBindList[errorIndex - 1].setComponentByPosition(
-            1, rfc1905.noSuchInstance, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, rfc1905.noSuchInstance, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
 
 apiPDU = PDUAPI()
@@ -105,15 +106,19 @@ class BulkPDUAPI(PDUAPI):
 
     def setDefaults(self, pdu):
         PDUAPI.setDefaults(self, pdu)
+
         pdu.setComponentByPosition(
-            0, getNextRequestID(), verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, getNextRequestID(), verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            1, self._nonRepeaters, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, self._nonRepeaters, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(
-            2, self._maxRepetitions, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._maxRepetitions, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         pdu.setComponentByPosition(3)
 
     @staticmethod
@@ -152,9 +157,11 @@ class BulkPDUAPI(PDUAPI):
         if R:
             for i in range(0, len(rspVarBinds) - N, R):
                 varBindRow = rspVarBinds[:N] + rspVarBinds[N + i:N + R + i]
+
                 # ignore stray OIDs / non-rectangular table
                 if len(varBindRow) == N + R:
                     varBindTable.append(varBindRow)
+
         elif N:
             varBindTable.append(rspVarBinds[:N])
 
@@ -175,9 +182,11 @@ class TrapPDUAPI(v1.PDUAPI):
 
     def setDefaults(self, pdu):
         v1.PDUAPI.setDefaults(self, pdu)
+
         varBinds = [(self.sysUpTime, self._zeroTime),
                     # generic trap
                     (self.snmpTrapOID, self._genTrap)]
+
         self.setVarBinds(pdu, varBinds)
 
 
@@ -188,16 +197,24 @@ class MessageAPI(v1.MessageAPI):
     _version = rfc1901.version.clone(1)
 
     def setDefaults(self, msg):
-        msg.setComponentByPosition(0, self._version, verifyConstraints=False, matchTags=False, matchConstraints=False)
-        msg.setComponentByPosition(1, self._community, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        msg.setComponentByPosition(
+            0, self._version, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
+        msg.setComponentByPosition(
+            1, self._community, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         return msg
 
     def getResponse(self, reqMsg):
         rspMsg = Message()
+
         self.setDefaults(rspMsg)
         self.setVersion(rspMsg, self.getVersion(reqMsg))
         self.setCommunity(rspMsg, self.getCommunity(reqMsg))
         self.setPDU(rspMsg, apiPDU.getResponse(self.getPDU(reqMsg)))
+
         return rspMsg
 
 
diff --git a/pysnmp/proto/api/verdec.py b/pysnmp/proto/api/verdec.py
index e6ec7fd9..142a68c2 100644
--- a/pysnmp/proto/api/verdec.py
+++ b/pysnmp/proto/api/verdec.py
@@ -18,13 +18,17 @@ def decodeMessageVersion(wholeMsg):
             wholeMsg, asn1Spec=univ.Sequence(),
             recursiveFlag=False, substrateFun=lambda a, b, c: (a, b[:c])
         )
+
         ver, wholeMsg = decoder.decode(
             wholeMsg, asn1Spec=univ.Integer(),
             recursiveFlag=False, substrateFun=lambda a, b, c: (a, b[:c])
         )
+
         if eoo.endOfOctets.isSameTypeWith(ver):
             raise ProtocolError('EOO at SNMP version component')
+
         return ver
 
     except PyAsn1Error as exc:
-        raise ProtocolError('Invalid BER at SNMP version component: %s' % exc)
+        raise ProtocolError('Invalid BER at SNMP version '
+                            'component: %s' % exc)
diff --git a/pysnmp/proto/cache.py b/pysnmp/proto/cache.py
index 9eae19c9..eed689ff 100644
--- a/pysnmp/proto/cache.py
+++ b/pysnmp/proto/cache.py
@@ -9,30 +9,30 @@ from pysnmp.proto import error
 
 class Cache(object):
     def __init__(self):
-        self.__cacheRepository = {}
+        self._cacheRepository = {}
 
     def add(self, index, **kwargs):
-        self.__cacheRepository[index] = kwargs
+        self._cacheRepository[index] = kwargs
         return index
 
     def pop(self, index):
-        if index in self.__cacheRepository:
-            cachedParams = self.__cacheRepository[index]
+        if index in self._cacheRepository:
+            cachedParams = self._cacheRepository[index]
         else:
             return
-        del self.__cacheRepository[index]
+        del self._cacheRepository[index]
         return cachedParams
 
     def update(self, index, **kwargs):
-        if index not in self.__cacheRepository:
+        if index not in self._cacheRepository:
             raise error.ProtocolError(
                 'Cache miss on update for %s' % kwargs
             )
-        self.__cacheRepository[index].update(kwargs)
+        self._cacheRepository[index].update(kwargs)
 
     def expire(self, cbFun, cbCtx):
-        for index, cachedParams in list(self.__cacheRepository.items()):
+        for index, cachedParams in list(self._cacheRepository.items()):
             if cbFun:
                 if cbFun(index, cachedParams, cbCtx):
-                    if index in self.__cacheRepository:
-                        del self.__cacheRepository[index]
+                    if index in self._cacheRepository:
+                        del self._cacheRepository[index]
diff --git a/pysnmp/proto/errind.py b/pysnmp/proto/errind.py
index 0c0dcb80..758a9ae1 100644
--- a/pysnmp/proto/errind.py
+++ b/pysnmp/proto/errind.py
@@ -10,30 +10,34 @@ class ErrorIndication(Exception):
     """SNMPv3 error-indication values"""
 
     def __init__(self, descr=None):
-        self.__value = self.__descr = self.__class__.__name__[0].lower() + self.__class__.__name__[1:]
+        self._value = (
+                self.__class__.__name__[0].lower() +
+                self.__class__.__name__[1:])
+        self._descr = self._value
+
         if descr:
-            self.__descr = descr
+            self._descr = descr
 
     def __eq__(self, other):
-        return self.__value == other
+        return self._value == other
 
     def __ne__(self, other):
-        return self.__value != other
+        return self._value != other
 
     def __lt__(self, other):
-        return self.__value < other
+        return self._value < other
 
     def __le__(self, other):
-        return self.__value <= other
+        return self._value <= other
 
     def __gt__(self, other):
-        return self.__value > other
+        return self._value > other
 
     def __ge__(self, other):
-        return self.__value >= other
+        return self._value >= other
 
     def __str__(self):
-        return self.__descr
+        return self._descr
 
 
 # SNMP message processing errors
@@ -42,84 +46,96 @@ class SerializationError(ErrorIndication):
     pass
 
 
-serializationError = SerializationError('SNMP message serialization error')
+serializationError = SerializationError(
+    'SNMP message serialization error')
 
 
 class DeserializationError(ErrorIndication):
     pass
 
 
-deserializationError = DeserializationError('SNMP message deserialization error')
+deserializationError = DeserializationError(
+    'SNMP message deserialization error')
 
 
 class ParseError(DeserializationError):
     pass
 
 
-parseError = ParseError('SNMP message deserialization error')
+parseError = ParseError(
+    'SNMP message deserialization error')
 
 
 class UnsupportedMsgProcessingModel(ErrorIndication):
     pass
 
 
-unsupportedMsgProcessingModel = UnsupportedMsgProcessingModel('Unknown SNMP message processing model ID encountered')
+unsupportedMsgProcessingModel = UnsupportedMsgProcessingModel(
+    'Unknown SNMP message processing model ID encountered')
 
 
 class UnknownPDUHandler(ErrorIndication):
     pass
 
 
-unknownPDUHandler = UnknownPDUHandler('Unhandled PDU type encountered')
+unknownPDUHandler = UnknownPDUHandler(
+    'Unhandled PDU type encountered')
 
 
 class UnsupportedPDUtype(ErrorIndication):
     pass
 
 
-unsupportedPDUtype = UnsupportedPDUtype('Unsupported SNMP PDU type encountered')
+unsupportedPDUtype = UnsupportedPDUtype(
+    'Unsupported SNMP PDU type encountered')
 
 
 class RequestTimedOut(ErrorIndication):
     pass
 
 
-requestTimedOut = RequestTimedOut('No SNMP response received before timeout')
+requestTimedOut = RequestTimedOut(
+    'No SNMP response received before timeout')
 
 
 class EmptyResponse(ErrorIndication):
     pass
 
 
-emptyResponse = EmptyResponse('Empty SNMP response message')
+emptyResponse = EmptyResponse(
+    'Empty SNMP response message')
 
 
 class NonReportable(ErrorIndication):
     pass
 
 
-nonReportable = NonReportable('Report PDU generation not attempted')
+nonReportable = NonReportable(
+    'Report PDU generation not attempted')
 
 
 class DataMismatch(ErrorIndication):
     pass
 
 
-dataMismatch = DataMismatch('SNMP request/response parameters mismatched')
+dataMismatch = DataMismatch(
+    'SNMP request/response parameters mismatched')
 
 
 class EngineIDMismatch(ErrorIndication):
     pass
 
 
-engineIDMismatch = EngineIDMismatch('SNMP engine ID mismatch encountered')
+engineIDMismatch = EngineIDMismatch(
+    'SNMP engine ID mismatch encountered')
 
 
 class UnknownEngineID(ErrorIndication):
     pass
 
 
-unknownEngineID = UnknownEngineID('Unknown SNMP engine ID encountered')
+unknownEngineID = UnknownEngineID(
+    'Unknown SNMP engine ID encountered')
 
 
 class TooBig(ErrorIndication):
@@ -133,14 +149,16 @@ class LoopTerminated(ErrorIndication):
     pass
 
 
-loopTerminated = LoopTerminated('Infinite SNMP entities talk terminated')
+loopTerminated = LoopTerminated(
+    'Infinite SNMP entities talk terminated')
 
 
 class InvalidMsg(ErrorIndication):
     pass
 
 
-invalidMsg = InvalidMsg('Invalid SNMP message header parameters encountered')
+invalidMsg = InvalidMsg(
+    'Invalid SNMP message header parameters encountered')
 
 
 # SNMP security modules errors
@@ -149,112 +167,128 @@ class UnknownCommunityName(ErrorIndication):
     pass
 
 
-unknownCommunityName = UnknownCommunityName('Unknown SNMP community name encountered')
+unknownCommunityName = UnknownCommunityName(
+    'Unknown SNMP community name encountered')
 
 
 class NoEncryption(ErrorIndication):
     pass
 
 
-noEncryption = NoEncryption('No encryption services configured')
+noEncryption = NoEncryption(
+    'No encryption services configured')
 
 
 class EncryptionError(ErrorIndication):
     pass
 
 
-encryptionError = EncryptionError('Ciphering services not available')
+encryptionError = EncryptionError(
+    'Ciphering services not available')
 
 
 class DecryptionError(ErrorIndication):
     pass
 
 
-decryptionError = DecryptionError('Ciphering services not available or ciphertext is broken')
+decryptionError = DecryptionError(
+    'Ciphering services not available or ciphertext is broken')
 
 
 class NoAuthentication(ErrorIndication):
     pass
 
 
-noAuthentication = NoAuthentication('No authentication services configured')
+noAuthentication = NoAuthentication(
+    'No authentication services configured')
 
 
 class AuthenticationError(ErrorIndication):
     pass
 
 
-authenticationError = AuthenticationError('Ciphering services not available or bad parameters')
+authenticationError = AuthenticationError(
+    'Ciphering services not available or bad parameters')
 
 
 class AuthenticationFailure(ErrorIndication):
     pass
 
 
-authenticationFailure = AuthenticationFailure('Authenticator mismatched')
+authenticationFailure = AuthenticationFailure(
+    'Authenticator mismatched')
 
 
 class UnsupportedAuthProtocol(ErrorIndication):
     pass
 
 
-unsupportedAuthProtocol = UnsupportedAuthProtocol('Authentication protocol is not supported')
+unsupportedAuthProtocol = UnsupportedAuthProtocol(
+    'Authentication protocol is not supported')
 
 
 class UnsupportedPrivProtocol(ErrorIndication):
     pass
 
 
-unsupportedPrivProtocol = UnsupportedPrivProtocol('Privacy protocol is not supported')
+unsupportedPrivProtocol = UnsupportedPrivProtocol(
+    'Privacy protocol is not supported')
 
 
 class UnknownSecurityName(ErrorIndication):
     pass
 
 
-unknownSecurityName = UnknownSecurityName('Unknown SNMP security name encountered')
+unknownSecurityName = UnknownSecurityName(
+    'Unknown SNMP security name encountered')
 
 
 class UnsupportedSecurityModel(ErrorIndication):
     pass
 
 
-unsupportedSecurityModel = UnsupportedSecurityModel('Unsupported SNMP security model')
+unsupportedSecurityModel = UnsupportedSecurityModel(
+    'Unsupported SNMP security model')
 
 
 class UnsupportedSecurityLevel(ErrorIndication):
     pass
 
 
-unsupportedSecurityLevel = UnsupportedSecurityLevel('Unsupported SNMP security level')
+unsupportedSecurityLevel = UnsupportedSecurityLevel(
+    'Unsupported SNMP security level')
 
 
 class NotInTimeWindow(ErrorIndication):
     pass
 
 
-notInTimeWindow = NotInTimeWindow('SNMP message timing parameters not in windows of trust')
+notInTimeWindow = NotInTimeWindow(
+    'SNMP message timing parameters not in windows of trust')
 
 
 class UnknownUserName(ErrorIndication):
     pass
 
 
-unknownUserName = UnknownUserName('Unknown USM user')
+unknownUserName = UnknownUserName(
+    'Unknown USM user')
 
 
 class WrongDigest(ErrorIndication):
     pass
 
 
-wrongDigest = WrongDigest('Wrong SNMP PDU digest')
+wrongDigest = WrongDigest(
+    'Wrong SNMP PDU digest')
 
 
 class ReportPduReceived(ErrorIndication):
     pass
 
 
-reportPduReceived = ReportPduReceived('Remote SNMP engine reported error')
+reportPduReceived = ReportPduReceived(
+    'Remote SNMP engine reported error')
 
 
 # SNMP access-control errors
@@ -263,36 +297,40 @@ class NoSuchView(ErrorIndication):
     pass
 
 
-noSuchView = NoSuchView('No such MIB view currently exists')
+noSuchView = NoSuchView(
+    'No such MIB view currently exists')
 
 
 class NoAccessEntry(ErrorIndication):
     pass
 
 
-
-noAccessEntry = NoAccessEntry('Access to MIB node denined')
+noAccessEntry = NoAccessEntry(
+    'Access to MIB node denined')
 
 
 class NoGroupName(ErrorIndication):
     pass
 
 
-noGroupName = NoGroupName('No such VACM group configured')
+noGroupName = NoGroupName(
+    'No such VACM group configured')
 
 
 class NoSuchContext(ErrorIndication):
     pass
 
 
-noSuchContext = NoSuchContext('SNMP context now found')
+noSuchContext = NoSuchContext(
+    'SNMP context now found')
 
 
 class NotInView(ErrorIndication):
     pass
 
 
-notInView = NotInView('Requested OID is out of MIB view')
+notInView = NotInView(
+    'Requested OID is out of MIB view')
 
 
 class AccessAllowed(ErrorIndication):
@@ -306,7 +344,8 @@ class OtherError(ErrorIndication):
     pass
 
 
-otherError = OtherError('Unspecified SNMP engine error occurred')
+otherError = OtherError(
+    'Unspecified SNMP engine error occurred')
 
 
 # SNMP Apps errors
@@ -315,4 +354,5 @@ class OidNotIncreasing(ErrorIndication):
     pass
 
 
-oidNotIncreasing = OidNotIncreasing('OID not increasing')
+oidNotIncreasing = OidNotIncreasing(
+    'OID not increasing')
diff --git a/pysnmp/proto/error.py b/pysnmp/proto/error.py
index 52e84642..4847bddf 100644
--- a/pysnmp/proto/error.py
+++ b/pysnmp/proto/error.py
@@ -23,8 +23,11 @@ class SnmpV3Error(ProtocolError):
 class StatusInformation(SnmpV3Error):
     def __init__(self, **kwargs):
         SnmpV3Error.__init__(self)
+
         self.__errorIndication = kwargs
-        debug.logger & (debug.FLAG_DSP | debug.FLAG_MP | debug.FLAG_SM | debug.FLAG_ACL) and debug.logger(
+
+        debug.logger & (debug.FLAG_DSP | debug.FLAG_MP |
+                        debug.FLAG_SM | debug.FLAG_ACL) and debug.logger(
             'StatusInformation: %s' % kwargs)
 
     def __str__(self):
diff --git a/pysnmp/proto/mpmod/base.py b/pysnmp/proto/mpmod/base.py
index 61b26662..835aca53 100644
--- a/pysnmp/proto/mpmod/base.py
+++ b/pysnmp/proto/mpmod/base.py
@@ -20,6 +20,7 @@ class AbstractMessageProcessingModel(object):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
+
         raise error.ProtocolError('method not implemented')
 
     def prepareResponseMessage(self, snmpEngine, messageProcessingModel,
@@ -27,15 +28,18 @@ class AbstractMessageProcessingModel(object):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU,
                                stateReference, statusInformation):
+
         raise error.ProtocolError('method not implemented')
 
     def prepareDataElements(self, snmpEngine, transportDomain,
                             transportAddress, wholeMsg):
+
         raise error.ProtocolError('method not implemented')
 
     def releaseStateInformation(self, sendPduHandle):
         try:
             self._cache.popBySendPduHandle(sendPduHandle)
+
         except error.ProtocolError:
             pass  # XXX maybe these should all follow some scheme?
 
diff --git a/pysnmp/proto/mpmod/cache.py b/pysnmp/proto/mpmod/cache.py
index 0cb343bd..265355a4 100644
--- a/pysnmp/proto/mpmod/cache.py
+++ b/pysnmp/proto/mpmod/cache.py
@@ -27,25 +27,37 @@ class Cache(object):
 
     def pushByStateRef(self, stateReference, **msgInfo):
         if stateReference in self.__stateReferenceIndex:
-            raise error.ProtocolError('Cache dup for stateReference=%s at %s' % (stateReference, self))
+            raise error.ProtocolError(
+                'Cache dup for stateReference=%s at %s' % (stateReference, self))
+
         expireAt = self.__expirationTimer + 600
+
         self.__stateReferenceIndex[stateReference] = msgInfo, expireAt
 
         # Schedule to expire
         if expireAt not in self.__expirationQueue:
             self.__expirationQueue[expireAt] = {}
+
         if 'stateReference' not in self.__expirationQueue[expireAt]:
             self.__expirationQueue[expireAt]['stateReference'] = {}
+
         self.__expirationQueue[expireAt]['stateReference'][stateReference] = 1
 
     def popByStateRef(self, stateReference):
         if stateReference in self.__stateReferenceIndex:
             cacheInfo = self.__stateReferenceIndex[stateReference]
+
         else:
-            raise error.ProtocolError('Cache miss for stateReference=%s at %s' % (stateReference, self))
+            raise error.ProtocolError(
+                'Cache miss for stateReference=%s at '
+                '%s' % (stateReference, self))
+
         del self.__stateReferenceIndex[stateReference]
+
         cacheEntry, expireAt = cacheInfo
+
         del self.__expirationQueue[expireAt]['stateReference'][stateReference]
+
         return cacheEntry
 
     # Client mode cache handling
@@ -56,9 +68,10 @@ class Cache(object):
     def pushByMsgId(self, msgId, **msgInfo):
         if msgId in self.__msgIdIndex:
             raise error.ProtocolError(
-                'Cache dup for msgId=%s at %s' % (msgId, self)
-            )
+                'Cache dup for msgId=%s at %s' % (msgId, self))
+
         expireAt = self.__expirationTimer + 600
+
         self.__msgIdIndex[msgId] = msgInfo, expireAt
 
         self.__sendPduHandleIdx[msgInfo['sendPduHandle']] = msgId
@@ -66,22 +79,29 @@ class Cache(object):
         # Schedule to expire
         if expireAt not in self.__expirationQueue:
             self.__expirationQueue[expireAt] = {}
+
         if 'msgId' not in self.__expirationQueue[expireAt]:
             self.__expirationQueue[expireAt]['msgId'] = {}
+
         self.__expirationQueue[expireAt]['msgId'][msgId] = 1
 
     def popByMsgId(self, msgId):
         if msgId in self.__msgIdIndex:
             cacheInfo = self.__msgIdIndex[msgId]
+
         else:
             raise error.ProtocolError(
-                'Cache miss for msgId=%s at %s' % (msgId, self)
-            )
+                'Cache miss for msgId=%s at %s' % (msgId, self))
+
         msgInfo, expireAt = cacheInfo
+
         del self.__sendPduHandleIdx[msgInfo['sendPduHandle']]
         del self.__msgIdIndex[msgId]
+
         cacheEntry, expireAt = cacheInfo
+
         del self.__expirationQueue[expireAt]['msgId'][msgId]
+
         return cacheEntry
 
     def popBySendPduHandle(self, sendPduHandle):
@@ -92,11 +112,15 @@ class Cache(object):
         # Uses internal clock to expire pending messages
         if self.__expirationTimer in self.__expirationQueue:
             cacheInfo = self.__expirationQueue[self.__expirationTimer]
+
             if 'stateReference' in cacheInfo:
                 for stateReference in cacheInfo['stateReference']:
                     del self.__stateReferenceIndex[stateReference]
+
             if 'msgId' in cacheInfo:
                 for msgId in cacheInfo['msgId']:
                     del self.__msgIdIndex[msgId]
+
             del self.__expirationQueue[self.__expirationTimer]
+
         self.__expirationTimer += 1
diff --git a/pysnmp/proto/mpmod/rfc2576.py b/pysnmp/proto/mpmod/rfc2576.py
index 8bad83c2..36011619 100644
--- a/pysnmp/proto/mpmod/rfc2576.py
+++ b/pysnmp/proto/mpmod/rfc2576.py
@@ -32,9 +32,11 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-        snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineId = snmpEngineId.syntax
 
         # rfc3412: 7.1.1b
@@ -42,8 +44,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             # serve unique PDU request-id
             msgID = self._cache.newMsgID()
             reqID = pdu.getComponentByPosition(0)
+
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareOutgoingMessage: PDU request-id %s replaced with unique ID %s' % (reqID, msgID))
+                'prepareOutgoingMessage: PDU request-id %s replaced with '
+                'unique ID %s' % (reqID, msgID))
 
         # rfc3412: 7.1.4
         # Since there's no SNMP engine identification in v1/2c,
@@ -56,17 +60,19 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = null
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: using contextEngineId %r contextName %r' % (contextEngineId, contextName))
+            'prepareOutgoingMessage: using contextEngineId %r contextName '
+            '%r' % (contextEngineId, contextName))
 
         # rfc3412: 7.1.6
-        scopedPDU = (contextEngineId, contextName, pdu)
+        scopedPDU = contextEngineId, contextName, pdu
 
         msg = self._snmpMsgSpec
+
         msg.setComponentByPosition(0, self.MESSAGE_PROCESSING_MODEL_ID)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # rfc3412: 7.1.7
         globalData = (msg,)
@@ -74,15 +80,15 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         k = int(securityModel)
         if k in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # rfc3412: 7.1.9.a & rfc2576: 5.2.1 --> no-op
 
-        snmpEngineMaxMessageSize, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                             'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # fix unique request-id right prior PDU serialization
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -90,12 +96,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             pdu.setComponentByPosition(0, msgID)
 
         # rfc3412: 7.1.9.b
-        (securityParameters,
-         wholeMsg) = smHandler.generateRequestMsg(
+        securityParameters, wholeMsg = smHandler.generateRequestMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, globalData,
             snmpEngineMaxMessageSize.syntax, securityModel,
-            snmpEngineId, securityName, securityLevel, scopedPDU
-        )
+            snmpEngineId, securityName, securityLevel, scopedPDU)
 
         # return original request-id right after PDU serialization
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -105,15 +109,16 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         # rfc3412: 7.1.9.c
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             # XXX rfc bug? why stateReference should be created?
-            self._cache.pushByMsgId(int(msgID), sendPduHandle=sendPduHandle,
-                                    reqID=reqID, snmpEngineId=snmpEngineId,
-                                    securityModel=securityModel,
-                                    securityName=securityName,
-                                    securityLevel=securityLevel,
-                                    contextEngineId=contextEngineId,
-                                    contextName=contextName,
-                                    transportDomain=transportDomain,
-                                    transportAddress=transportAddress)
+            self._cache.pushByMsgId(
+                int(msgID), sendPduHandle=sendPduHandle,
+                reqID=reqID, snmpEngineId=snmpEngineId,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                transportDomain=transportDomain,
+                transportAddress=transportAddress)
 
         communityName = msg.getComponentByPosition(1)  # for observer
 
@@ -128,11 +133,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName,
                  communityName=communityName,
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc2576.prepareOutgoingMessage'
-        )
+            snmpEngine, 'rfc2576.prepareOutgoingMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -142,9 +146,11 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU, stateReference,
                                statusInformation):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
-        snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineId, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineId = snmpEngineId.syntax
 
         # rfc3412: 7.1.2.b
@@ -152,6 +158,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             raise error.StatusInformation(errorIndication=errind.nonReportable)
 
         cachedParams = self._cache.popByStateRef(stateReference)
+
         msgID = cachedParams['msgID']
         reqID = cachedParams['reqID']
         contextEngineId = cachedParams['contextEngineId']
@@ -165,7 +172,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         transportAddress = cachedParams['transportAddress']
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: cache read msgID %s transportDomain %s transportAddress %s by stateReference %s' % (
+            'prepareResponseMessage: cache read msgID %s transportDomain %s '
+            'transportAddress %s by stateReference %s' % (
                 msgID, transportDomain, transportAddress, stateReference))
 
         # rfc3412: 7.1.3
@@ -189,14 +197,15 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         scopedPDU = (contextEngineId, contextName, pdu)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: using contextEngineId %r contextName %r' % (contextEngineId, contextName))
+            'prepareResponseMessage: using contextEngineId %r contextName '
+            '%r' % (contextEngineId, contextName))
 
         msg = self._snmpMsgSpec
         msg.setComponentByPosition(0, messageProcessingModel)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # att: msgId not set back to PDU as it's up to responder app
 
@@ -206,20 +215,19 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         k = int(securityModel)
         if k in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # set original request-id right prior to PDU serialization
         pdu.setComponentByPosition(0, reqID)
 
         # rfc3412: 7.1.8.a
-        (securityParameters, wholeMsg) = smHandler.generateResponseMsg(
+        securityParameters, wholeMsg = smHandler.generateResponseMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, globalData,
             maxMessageSize, securityModel, snmpEngineId, securityName,
-            securityLevel, scopedPDU, securityStateReference
-        )
+            securityLevel, scopedPDU, securityStateReference)
 
         # recover unique request-id right after PDU serialization
         pdu.setComponentByPosition(0, msgID)
@@ -235,11 +243,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                  contextName=contextName,
                  securityEngineId=snmpEngineId,
                  communityName=msg.getComponentByPosition(1),
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc2576.prepareResponseMessage'
-        )
+            snmpEngine, 'rfc2576.prepareResponseMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -247,12 +254,14 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
 
     def prepareDataElements(self, snmpEngine, transportDomain,
                             transportAddress, wholeMsg):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
         # rfc3412: 7.2.2
         msg, restOfWholeMsg = decoder.decode(wholeMsg, asn1Spec=self._snmpMsgSpec)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareDataElements: %s' % (msg.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(msg):
             raise error.StatusInformation(errorIndication=errind.parseError)
@@ -261,8 +270,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
         msgVersion = msg.getComponentByPosition(0)
 
         # rfc2576: 5.2.1
-        snmpEngineMaxMessageSize, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
         communityName = msg.getComponentByPosition(1)
+
         # transportDomain identifies local endpoint
         securityParameters = (communityName, (transportDomain, transportAddress))
         messageProcessingModel = int(msg.getComponentByPosition(0))
@@ -293,7 +304,8 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             )
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: SM returned securityEngineId %r securityName %r' % (securityEngineId, securityName))
+                'prepareDataElements: SM returned securityEngineId %r '
+                'securityName %r' % (securityEngineId, securityName))
 
         except error.StatusInformation as exc:
             statusInformation = exc
@@ -305,11 +317,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      securityModel=securityModel,
                      securityLevel=securityLevel,
                      securityParameters=securityParameters,
-                     statusInformation=statusInformation)
-            )
+                     statusInformation=statusInformation))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:sm-failure'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:sm-failure')
 
             raise
 
@@ -332,6 +343,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.2.10a
             try:
                 cachedReqParams = self._cache.popByMsgId(int(msgID))
+
             except error.ProtocolError:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(errorIndication=errind.dataMismatch)
@@ -340,11 +352,12 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             pdu.setComponentByPosition(0, cachedReqParams['reqID'])
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: unique PDU request-id %s replaced with original ID %s' % (
-                    msgID, cachedReqParams['reqID']))
+                'prepareDataElements: unique PDU request-id %s replaced with '
+                'original ID %s' % (msgID, cachedReqParams['reqID']))
 
             # 7.2.10b
             sendPduHandle = cachedReqParams['sendPduHandle']
+
         else:
             sendPduHandle = None
 
@@ -363,7 +376,9 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                     securityLevel != cachedReqParams['securityLevel'] or
                     contextEngineId != cachedReqParams['contextEngineId'] or
                     contextName != cachedReqParams['contextName']):
+
                 smHandler.releaseStateInformation(securityStateReference)
+
                 raise error.StatusInformation(errorIndication=errind.dataMismatch)
 
             stateReference = None
@@ -379,11 +394,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:response'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:response')
 
             # rfc3412: 7.2.12c
             smHandler.releaseStateInformation(securityStateReference)
@@ -401,19 +415,23 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
             reqID = pdu.getComponentByPosition(0)
             msgID = self._cache.newMsgID()
             pdu.setComponentByPosition(0, msgID)
+
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: received PDU request-id %s replaced with unique ID %s' % (reqID, msgID))
+                'prepareDataElements: received PDU request-id %s replaced with '
+                'unique ID %s' % (reqID, msgID))
 
             # rfc3412: 7.2.13a
-            snmpEngineId, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+            snmpEngineId, = mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+
             if securityEngineId != snmpEngineId.syntax:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(
-                    errorIndication=errind.engineIDMismatch
-                )
+                    errorIndication=errind.engineIDMismatch)
 
             # rfc3412: 7.2.13b
             stateReference = self._cache.newStateReference()
+
             self._cache.pushByStateRef(
                 stateReference, msgVersion=messageProcessingModel,
                 msgID=msgID, reqID=reqID, contextEngineId=contextEngineId,
@@ -437,14 +455,14 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:confirmed'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:confirmed')
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: cached by new stateReference %s' % stateReference)
+                'prepareDataElements: cached by new stateReference '
+                '%s' % stateReference)
 
             # rfc3412: 7.2.13c
             return (messageProcessingModel, securityModel, securityName,
@@ -469,11 +487,10 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                      contextName=contextName,
                      securityEngineId=securityEngineId,
                      communityName=communityName,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc2576.prepareDataElements:unconfirmed'
-            )
+                snmpEngine, 'rfc2576.prepareDataElements:unconfirmed')
 
             # This is not specified explicitly in RFC
             smHandler.releaseStateInformation(securityStateReference)
@@ -485,6 +502,7 @@ class SnmpV1MessageProcessingModel(AbstractMessageProcessingModel):
                     stateReference)
 
         smHandler.releaseStateInformation(securityStateReference)
+
         raise error.StatusInformation(errorIndication=errind.unsupportedPDUtype)
 
 
diff --git a/pysnmp/proto/mpmod/rfc3412.py b/pysnmp/proto/mpmod/rfc3412.py
index 6ff9fa8d..20852db6 100644
--- a/pysnmp/proto/mpmod/rfc3412.py
+++ b/pysnmp/proto/mpmod/rfc3412.py
@@ -30,49 +30,53 @@ class ScopedPDU(univ.Sequence):
     componentType = namedtype.NamedTypes(
         namedtype.NamedType('contextEngineId', univ.OctetString()),
         namedtype.NamedType('contextName', univ.OctetString()),
-        namedtype.NamedType('data', rfc1905.PDUs())
-    )
+        namedtype.NamedType('data', rfc1905.PDUs()))
 
 
 class ScopedPduData(univ.Choice):
     componentType = namedtype.NamedTypes(
         namedtype.NamedType('plaintext', ScopedPDU()),
-        namedtype.NamedType('encryptedPDU', univ.OctetString()),
-    )
+        namedtype.NamedType('encryptedPDU', univ.OctetString()))
 
 
 class HeaderData(univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgID',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgMaxSize',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(484, 2147483647))),
-        namedtype.NamedType('msgFlags', univ.OctetString().subtype(subtypeSpec=constraint.ValueSizeConstraint(1, 1))),
+        namedtype.NamedType(
+            'msgID', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgMaxSize', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(484, 2147483647))),
+        namedtype.NamedType(
+            'msgFlags', univ.OctetString().subtype(
+                subtypeSpec=constraint.ValueSizeConstraint(1, 1))),
         # NOTE (etingof): constrain SNMPv3 message to only USM+ security models
         # because SNMPv1/v2c seems incompatible in pysnmp implementation, not sure
         # if it's intended by the SNMP standard at all...
-        namedtype.NamedType('msgSecurityModel',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(3, 2147483647)))
-    )
+        namedtype.NamedType(
+            'msgSecurityModel', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(3, 2147483647))))
 
 
 class SNMPv3Message(univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgVersion',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgVersion', univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
         namedtype.NamedType('msgGlobalData', HeaderData()),
         namedtype.NamedType('msgSecurityParameters', univ.OctetString()),
-        namedtype.NamedType('msgData', ScopedPduData())
-    )
+        namedtype.NamedType('msgData', ScopedPduData()))
 
 
 # XXX move somewhere?
-_snmpErrors = {(1, 3, 6, 1, 6, 3, 15, 1, 1, 1, 0): errind.unsupportedSecurityLevel,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 2, 0): errind.notInTimeWindow,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 3, 0): errind.unknownUserName,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 4, 0): errind.unknownEngineID,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 5, 0): errind.wrongDigest,
-               (1, 3, 6, 1, 6, 3, 15, 1, 1, 6, 0): errind.decryptionError}
+_snmpErrors = {
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 1, 0): errind.unsupportedSecurityLevel,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 2, 0): errind.notInTimeWindow,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 3, 0): errind.unknownUserName,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 4, 0): errind.unknownEngineID,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 5, 0): errind.wrongDigest,
+    (1, 3, 6, 1, 6, 3, 15, 1, 1, 6, 0): errind.decryptionError
+}
 
 
 class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
@@ -80,26 +84,28 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
     SNMP_MSG_SPEC = SNMPv3Message
 
     _emptyStr = univ.OctetString('')
-    _msgFlags = {0: univ.OctetString('\x00'),
-                 1: univ.OctetString('\x01'),
-                 3: univ.OctetString('\x03'),
-                 4: univ.OctetString('\x04'),
-                 5: univ.OctetString('\x05'),
-                 7: univ.OctetString('\x07')}
+    _msgFlags = {
+        0: univ.OctetString('\x00'),
+        1: univ.OctetString('\x01'),
+        3: univ.OctetString('\x03'),
+        4: univ.OctetString('\x04'),
+        5: univ.OctetString('\x05'),
+        7: univ.OctetString('\x07')
+    }
 
     def __init__(self):
         AbstractMessageProcessingModel.__init__(self)
-        self.__scopedPDU = ScopedPDU()
-        self.__engineIdCache = {}
-        self.__engineIdCacheExpQueue = {}
-        self.__expirationTimer = 0
+        self._scopedPDU = ScopedPDU()
+        self._engineIdCache = {}
+        self._engineIdCacheExpQueue = {}
+        self._expirationTimer = 0
 
     def getPeerEngineInfo(self, transportDomain, transportAddress):
         k = transportDomain, transportAddress
-        if k in self.__engineIdCache:
-            return (self.__engineIdCache[k]['securityEngineId'],
-                    self.__engineIdCache[k]['contextEngineId'],
-                    self.__engineIdCache[k]['contextName'])
+        if k in self._engineIdCache:
+            return (self._engineIdCache[k]['securityEngineId'],
+                    self._engineIdCache[k]['contextEngineId'],
+                    self._engineIdCache[k]['contextName'])
         else:
             return None, None, None
 
@@ -109,29 +115,35 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                                securityModel, securityName, securityLevel,
                                contextEngineId, contextName, pduVersion,
                                pdu, expectResponse, sendPduHandle):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                              'snmpEngineID')
+
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.1.1b
         msgID = self._cache.newMsgID()
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: new msgID %s' % msgID)
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareOutgoingMessage: new msgID %s' % msgID)
+
+        k = transportDomain, transportAddress
+        if k in self._engineIdCache:
+            peerSnmpEngineData = self._engineIdCache[k]
 
-        k = (transportDomain, transportAddress)
-        if k in self.__engineIdCache:
-            peerSnmpEngineData = self.__engineIdCache[k]
         else:
             peerSnmpEngineData = None
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: peer SNMP engine data %s for transport %s, address %s' % (
-                peerSnmpEngineData, transportDomain, transportAddress))
+            'prepareOutgoingMessage: peer SNMP engine data %s '
+            'for transport %s, address '
+            '%s' % (peerSnmpEngineData, transportDomain, transportAddress))
 
         # 7.1.4
         if contextEngineId is None:
             if peerSnmpEngineData is None:
                 contextEngineId = snmpEngineID
+
             else:
                 contextEngineId = peerSnmpEngineData['contextEngineId']
                 # Defaulting contextEngineID to securityEngineId should
@@ -144,88 +156,98 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = self._emptyStr
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: using contextEngineId %r, contextName %r' % (contextEngineId, contextName))
+            'prepareOutgoingMessage: using contextEngineId %r, contextName '
+            '%r' % (contextEngineId, contextName))
 
         # 7.1.6
-        scopedPDU = self.__scopedPDU
+        scopedPDU = self._scopedPDU
         scopedPDU.setComponentByPosition(0, contextEngineId)
         scopedPDU.setComponentByPosition(1, contextName)
         scopedPDU.setComponentByPosition(2)
         scopedPDU.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7
         msg = self._snmpMsgSpec
 
         # 7.1.7a
         msg.setComponentByPosition(
-            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
+
         headerData = msg.setComponentByPosition(1).getComponentByPosition(1)
 
         # 7.1.7b
-        headerData.setComponentByPosition(0, msgID, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        headerData.setComponentByPosition(
+            0, msgID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        snmpEngineMaxMessageSize, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
             '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # 7.1.7c
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(
-            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7d
         msgFlags = 0
         if securityLevel == 1:
             pass
+
         elif securityLevel == 2:
             msgFlags |= 0x01
+
         elif securityLevel == 3:
             msgFlags |= 0x03
+
         else:
             raise error.ProtocolError(
-                'Unknown securityLevel %s' % securityLevel
-            )
+                'Unknown securityLevel %s' % securityLevel)
 
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             msgFlags |= 0x04
 
         headerData.setComponentByPosition(
-            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._msgFlags[msgFlags], verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7e
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(3, int(securityModel))
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareOutgoingMessage: %s' % (msg.prettyPrint(),))
 
         if securityModel in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[securityModel]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedSecurityModel
-            )
+                errorIndication=errind.unsupportedSecurityModel)
 
         # 7.1.9.a
         if pdu.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
             securityEngineId = snmpEngineID
+
         else:
             if peerSnmpEngineData is None:
                 # Force engineID discovery (rfc3414, 4)
                 securityEngineId = securityName = self._emptyStr
                 securityLevel = 1
+
                 # Clear possible auth&priv flags
                 headerData.setComponentByPosition(
-                    2, self._msgFlags[msgFlags & 0xfc], verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
+                    2, self._msgFlags[msgFlags & 0xfc], verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
+
                 # XXX
-                scopedPDU = self.__scopedPDU
+                scopedPDU = self._scopedPDU
                 scopedPDU.setComponentByPosition(
-                    0, self._emptyStr, verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
+                    0, self._emptyStr, verifyConstraints=False, matchTags=False,
+                    matchConstraints=False)
                 scopedPDU.setComponentByPosition(1, contextName)
                 scopedPDU.setComponentByPosition(2)
 
@@ -234,19 +256,22 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                 pMod.apiPDU.setDefaults(emptyPdu)
 
                 scopedPDU.getComponentByPosition(2).setComponentByType(
-                    emptyPdu.tagSet, emptyPdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-                )
-                debug.logger & debug.FLAG_MP and debug.logger('prepareOutgoingMessage: force engineID discovery')
+                    emptyPdu.tagSet, emptyPdu, verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
+
+                debug.logger & debug.FLAG_MP and debug.logger(
+                    'prepareOutgoingMessage: force engineID discovery')
+
             else:
                 securityEngineId = peerSnmpEngineData['securityEngineId']
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareOutgoingMessage: securityModel %r, securityEngineId %r, securityName %r, securityLevel %r' % (
-                securityModel, securityEngineId, securityName, securityLevel))
+            'prepareOutgoingMessage: securityModel %r, securityEngineId %r, '
+            'securityName %r, securityLevel '
+            '%r' % (securityModel, securityEngineId, securityName, securityLevel))
 
         # 7.1.9.b
-        (securityParameters,
-         wholeMsg) = smHandler.generateRequestMsg(
+        securityParameters, wholeMsg = smHandler.generateRequestMsg(
             snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
             snmpEngineMaxMessageSize.syntax, securityModel,
             securityEngineId, securityName, securityLevel, scopedPDU
@@ -259,15 +284,16 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.1.9.c
         if pdu.tagSet in rfc3411.CONFIRMED_CLASS_PDUS:
             # XXX rfc bug? why stateReference should be created?
-            self._cache.pushByMsgId(msgID, sendPduHandle=sendPduHandle,
-                                    msgID=msgID, snmpEngineID=snmpEngineID,
-                                    securityModel=securityModel,
-                                    securityName=securityName,
-                                    securityLevel=securityLevel,
-                                    contextEngineId=contextEngineId,
-                                    contextName=contextName,
-                                    transportDomain=transportDomain,
-                                    transportAddress=transportAddress)
+            self._cache.pushByMsgId(
+                msgID, sendPduHandle=sendPduHandle,
+                msgID=msgID, snmpEngineID=snmpEngineID,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                transportDomain=transportDomain,
+                transportAddress=transportAddress)
 
         snmpEngine.observer.storeExecutionContext(
             snmpEngine, 'rfc3412.prepareOutgoingMessage',
@@ -292,7 +318,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                                contextEngineId, contextName, pduVersion,
                                pdu, maxSizeResponseScopedPDU, stateReference,
                                statusInformation):
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.1.2.b
@@ -309,13 +338,15 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         transportDomain = cachedParams['transportDomain']
         transportAddress = cachedParams['transportAddress']
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: stateReference %s' % stateReference)
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: stateReference %s' % stateReference)
 
         # 7.1.3
         if statusInformation is not None and 'oid' in statusInformation:
             # 7.1.3a
             if pdu is None:
                 pduType = None
+
             else:
                 requestID = pdu.getComponentByPosition(0)
                 pduType = pdu.tagSet
@@ -325,16 +356,18 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     pduType is not None and
                     pduType not in rfc3411.CONFIRMED_CLASS_PDUS):
                 raise error.StatusInformation(
-                    errorIndication=errind.loopTerminated
-                )
+                    errorIndication=errind.loopTerminated)
 
             # 7.1.3c
             reportPDU = rfc1905.ReportPDU()
-            pMod.apiPDU.setVarBinds(reportPDU, ((statusInformation['oid'], statusInformation['val']),))
+            pMod.apiPDU.setVarBinds(
+                reportPDU, ((statusInformation['oid'], statusInformation['val']),))
             pMod.apiPDU.setErrorStatus(reportPDU, 0)
             pMod.apiPDU.setErrorIndex(reportPDU, 0)
+
             if pdu is None:
                 pMod.apiPDU.setRequestID(reportPDU, 0)
+
             else:
                 # noinspection PyUnboundLocalVariable
                 pMod.apiPDU.setRequestID(reportPDU, requestID)
@@ -342,18 +375,21 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.1.3d.1
             if 'securityLevel' in statusInformation:
                 securityLevel = statusInformation['securityLevel']
+
             else:
                 securityLevel = 1
 
             # 7.1.3d.2
             if 'contextEngineId' in statusInformation:
                 contextEngineId = statusInformation['contextEngineId']
+
             else:
                 contextEngineId = snmpEngineID
 
             # 7.1.3d.3
             if 'contextName' in statusInformation:
                 contextName = statusInformation['contextName']
+
             else:
                 contextName = ""
 
@@ -361,7 +397,8 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             pdu = reportPDU
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareResponseMessage: prepare report PDU for statusInformation %s' % statusInformation)
+                'prepareResponseMessage: prepare report PDU for '
+                'statusInformation %s' % statusInformation)
         # 7.1.4
         if not contextEngineId:
             contextEngineId = snmpEngineID  # XXX impl-dep manner
@@ -371,47 +408,54 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             contextName = self._emptyStr
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: using contextEngineId %r, contextName %r' % (contextEngineId, contextName))
+            'prepareResponseMessage: using contextEngineId %r, contextName '
+            '%r' % (contextEngineId, contextName))
 
         # 7.1.6
-        scopedPDU = self.__scopedPDU
+        scopedPDU = self._scopedPDU
         scopedPDU.setComponentByPosition(0, contextEngineId)
         scopedPDU.setComponentByPosition(1, contextName)
         scopedPDU.setComponentByPosition(2)
         scopedPDU.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7
         msg = self._snmpMsgSpec
 
         # 7.1.7a
         msg.setComponentByPosition(
-            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, self.MESSAGE_PROCESSING_MODEL_ID, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         headerData = msg.setComponentByPosition(1).getComponentByPosition(1)
 
         # 7.1.7b
-        headerData.setComponentByPosition(0, msgID, verifyConstraints=False, matchTags=False, matchConstraints=False)
+        headerData.setComponentByPosition(
+            0, msgID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        snmpEngineMaxMessageSize, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
             '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
 
         # 7.1.7c
         # XXX need to coerce MIB value as it has incompatible constraints set
         headerData.setComponentByPosition(
-            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineMaxMessageSize.syntax, verifyConstraints=False,
+            matchTags=False, matchConstraints=False)
 
         # 7.1.7d
         msgFlags = 0
+
         if securityLevel == 1:
             pass
+
         elif securityLevel == 2:
             msgFlags |= 0x01
+
         elif securityLevel == 3:
             msgFlags |= 0x03
+
         else:
             raise error.ProtocolError('Unknown securityLevel %s' % securityLevel)
 
@@ -419,39 +463,43 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             msgFlags |= 0x04
 
         headerData.setComponentByPosition(
-            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, self._msgFlags[msgFlags], verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 7.1.7e
         headerData.setComponentByPosition(
-            3, securityModel, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            3, securityModel, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: %s' % (msg.prettyPrint(),))
 
         if securityModel in snmpEngine.securityModels:
             smHandler = snmpEngine.securityModels[securityModel]
+
         else:
-            raise error.StatusInformation(errorIndication=errind.unsupportedSecurityModel)
+            raise error.StatusInformation(
+                errorIndication=errind.unsupportedSecurityModel)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareResponseMessage: securityModel %r, securityEngineId %r, securityName %r, securityLevel %r' % (
+            'prepareResponseMessage: securityModel %r, securityEngineId %r, '
+            'securityName %r, securityLevel %r' % (
                 securityModel, snmpEngineID, securityName, securityLevel))
 
         # 7.1.8a
         try:
-            (securityParameters,
-             wholeMsg) = smHandler.generateResponseMsg(
+            securityParameters, wholeMsg = smHandler.generateResponseMsg(
                 snmpEngine, self.MESSAGE_PROCESSING_MODEL_ID, msg,
                 snmpEngineMaxMessageSize.syntax, securityModel,
                 snmpEngineID, securityName, securityLevel, scopedPDU,
-                securityStateReference
-            )
+                securityStateReference)
+
         except error.StatusInformation:
             # 7.1.8.b
             raise
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareResponseMessage: SM finished')
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareResponseMessage: SM finished')
 
         # Message size constraint verification
         if len(wholeMsg) > min(snmpEngineMaxMessageSize.syntax, maxMessageSize):
@@ -468,11 +516,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName,
                  securityEngineId=snmpEngineID,
-                 pdu=pdu)
-        )
+                 pdu=pdu))
+
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3412.prepareResponseMessage'
-        )
+            snmpEngine, 'rfc3412.prepareResponseMessage')
 
         return transportDomain, transportAddress, wholeMsg
 
@@ -483,11 +530,14 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.2.2
         msg, restOfwholeMsg = decoder.decode(wholeMsg, asn1Spec=self._snmpMsgSpec)
 
-        debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'prepareDataElements: %s' % (msg.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(msg):
             raise error.StatusInformation(errorIndication=errind.parseError)
 
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
         # 7.2.3
         headerData = msg.getComponentByPosition(1)
         msgVersion = messageProcessingModel = msg.getComponentByPosition(0)
@@ -498,12 +548,12 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         securityParameters = msg.getComponentByPosition(2)
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareDataElements: msg data msgVersion %s msgID %s securityModel %s' % (
-                msgVersion, msgID, securityModel))
+            'prepareDataElements: msg data msgVersion %s msgID %s '
+            'securityModel %s' % (msgVersion, msgID, securityModel))
 
         # 7.2.4
         if securityModel not in snmpEngine.securityModels:
-            snmpUnknownSecurityModels, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+            snmpUnknownSecurityModels, = mibBuilder.importSymbols(
                 '__SNMP-MPD-MIB', 'snmpUnknownSecurityModels')
             snmpUnknownSecurityModels.syntax += 1
             raise error.StatusInformation(errorIndication=errind.unsupportedSecurityModel)
@@ -511,22 +561,28 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
         # 7.2.5
         if msgFlags & 0x03 == 0x00:
             securityLevel = 1
+
         elif (msgFlags & 0x03) == 0x01:
             securityLevel = 2
+
         elif (msgFlags & 0x03) == 0x03:
             securityLevel = 3
+
         else:
-            snmpInvalidMsgs, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB', 'snmpInvalidMsgs')
+            snmpInvalidMsgs, = mibBuilder.importSymbols(
+                '__SNMP-MPD-MIB', 'snmpInvalidMsgs')
             snmpInvalidMsgs.syntax += 1
             raise error.StatusInformation(errorIndication=errind.invalidMsg)
 
         if msgFlags & 0x04:
             reportableFlag = 1
+
         else:
             reportableFlag = 0
 
         # 7.2.6
         smHandler = snmpEngine.securityModels[securityModel]
+
         try:
             (securityEngineId,
              securityName,
@@ -535,15 +591,17 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
              securityStateReference) = smHandler.processIncomingMsg(
                 snmpEngine, messageProcessingModel, maxMessageSize,
                 securityParameters, securityModel, securityLevel,
-                wholeMsg, msg
-            )
-            debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: SM succeeded')
+                wholeMsg, msg)
+
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'prepareDataElements: SM succeeded')
 
         except error.StatusInformation as exc:
             statusInformation = exc
 
             debug.logger & debug.FLAG_MP and debug.logger(
-                'prepareDataElements: SM failed, statusInformation %s' % statusInformation)
+                'prepareDataElements: SM failed, statusInformation '
+                '%s' % statusInformation)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:sm-failure',
@@ -552,11 +610,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      securityModel=securityModel,
                      securityLevel=securityLevel,
                      securityParameters=securityParameters,
-                     statusInformation=statusInformation)
-            )
+                     statusInformation=statusInformation))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:sm-failure'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:sm-failure')
 
             if 'errorIndication' in statusInformation:
                 # 7.2.6a
@@ -565,16 +622,20 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     securityStateReference = statusInformation['securityStateReference']
                     contextEngineId = statusInformation['contextEngineId']
                     contextName = statusInformation['contextName']
+
                     if 'scopedPDU' in statusInformation:
                         scopedPDU = statusInformation['scopedPDU']
                         pdu = scopedPDU.getComponentByPosition(2).getComponent()
+
                     else:
                         pdu = None
+
                     maxSizeResponseScopedPDU = statusInformation['maxSizeResponseScopedPDU']
                     securityName = None  # XXX secmod cache used
 
                     # 7.2.6a2
                     stateReference = self._cache.newStateReference()
+
                     self._cache.pushByStateRef(
                         stateReference, msgVersion=messageProcessingModel,
                         msgID=msgID, contextEngineId=contextEngineId,
@@ -585,8 +646,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                         msgMaxSize=maxMessageSize,
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                         transportDomain=transportDomain,
-                        transportAddress=transportAddress
-                    )
+                        transportAddress=transportAddress)
 
                     # 7.2.6a3
                     try:
@@ -594,16 +654,18 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                             snmpEngine, 3, securityModel, securityName,
                             securityLevel, contextEngineId, contextName,
                             1, pdu, maxSizeResponseScopedPDU, stateReference,
-                            statusInformation
-                        )
+                            statusInformation)
+
                     except error.StatusInformation:
                         pass
 
-                    debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: error reported')
+                    debug.logger & debug.FLAG_MP and debug.logger(
+                        'prepareDataElements: error reported')
 
             # 7.2.6b
             if sys.version_info[0] <= 2:
                 raise statusInformation
+
             else:
                 origTraceback = sys.exc_info()[2]
 
@@ -616,31 +678,36 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     del origTraceback
         else:
             # Sniff for engineIdCache
-            k = (transportDomain, transportAddress)
-            if k not in self.__engineIdCache:
+            k = transportDomain, transportAddress
+            if k not in self._engineIdCache:
                 contextEngineId = scopedPDU[0]
                 contextName = scopedPDU[1]
+
                 pdus = scopedPDU[2]
                 pdu = pdus.getComponent()
+
                 # Here we assume that authentic/default EngineIDs
                 # come only in the course of engine-to-engine communication.
                 if pdu.tagSet in rfc3411.INTERNAL_CLASS_PDUS:
-                    self.__engineIdCache[k] = {
+                    self._engineIdCache[k] = {
                         'securityEngineId': securityEngineId,
                         'contextEngineId': contextEngineId,
                         'contextName': contextName
                     }
 
-                    expireAt = int(self.__expirationTimer + 300 / snmpEngine.transportDispatcher.getTimerResolution())
-                    if expireAt not in self.__engineIdCacheExpQueue:
-                        self.__engineIdCacheExpQueue[expireAt] = []
-                    self.__engineIdCacheExpQueue[expireAt].append(k)
+                    timerResolution = snmpEngine.transportDispatcher.getTimerResolution()
+                    expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+                    if expireAt not in self._engineIdCacheExpQueue:
+                        self._engineIdCacheExpQueue[expireAt] = []
+
+                    self._engineIdCacheExpQueue[expireAt].append(k)
 
                     debug.logger & debug.FLAG_MP and debug.logger(
                         'prepareDataElements: cache securityEngineId %r for %r %r' % (
                             securityEngineId, transportDomain, transportAddress))
 
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+        snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
         snmpEngineID = snmpEngineID.syntax
 
         # 7.2.7 XXX PDU would be parsed here?
@@ -662,33 +729,39 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             # 7.2.10a
             try:
                 cachedReqParams = self._cache.popByMsgId(msgID)
+
             except error.ProtocolError:
                 smHandler.releaseStateInformation(securityStateReference)
-                raise error.StatusInformation(
-                    errorIndication=errind.dataMismatch
-                )
+                raise error.StatusInformation(errorIndication=errind.dataMismatch)
+
             # 7.2.10b
             sendPduHandle = cachedReqParams['sendPduHandle']
+
         else:
             sendPduHandle = None
 
         debug.logger & debug.FLAG_MP and debug.logger(
-            'prepareDataElements: using sendPduHandle %s for msgID %s' % (sendPduHandle, msgID))
+            'prepareDataElements: using sendPduHandle %s for msgID '
+            '%s' % (sendPduHandle, msgID))
 
         # 7.2.11
         if pduType in rfc3411.INTERNAL_CLASS_PDUS:
             # 7.2.11a
             varBinds = pMod.apiPDU.getVarBinds(pdu)
+
             if varBinds:
+                errorIndication = _snmpErrors.get(
+                    varBinds[0][0],
+                    errind.ReportPduReceived(varBinds[0][0].prettyPrint()))
+
                 statusInformation = error.StatusInformation(
-                    errorIndication=_snmpErrors.get(varBinds[0][0], errind.ReportPduReceived(varBinds[0][0].prettyPrint())),
+                    errorIndication=errorIndication,
                     oid=varBinds[0][0], val=varBinds[0][1],
-                    sendPduHandle=sendPduHandle
-                )
+                    sendPduHandle=sendPduHandle)
+
             else:
                 statusInformation = error.StatusInformation(
-                    sendPduHandle=sendPduHandle
-                )
+                    sendPduHandle=sendPduHandle)
 
             # 7.2.11b (incomplete implementation)
 
@@ -702,11 +775,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:internal'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:internal')
 
             # 7.2.11c
             smHandler.releaseStateInformation(securityStateReference)
@@ -730,10 +802,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     securityLevel != cachedReqParams['securityLevel'] or
                     contextEngineId != cachedReqParams['contextEngineId'] or
                     contextName != cachedReqParams['contextName']):
+
                 smHandler.releaseStateInformation(securityStateReference)
-                raise error.StatusInformation(
-                    errorIndication=errind.dataMismatch
-                )
+
+                raise error.StatusInformation(errorIndication=errind.dataMismatch)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:response',
@@ -745,11 +817,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:response'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:response')
 
             # 7.2.12c
             smHandler.releaseStateInformation(securityStateReference)
@@ -768,11 +839,11 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
             if securityEngineId != snmpEngineID:
                 smHandler.releaseStateInformation(securityStateReference)
                 raise error.StatusInformation(
-                    errorIndication=errind.engineIDMismatch
-                )
+                    errorIndication=errind.engineIDMismatch)
 
             # 7.2.13b
             stateReference = self._cache.newStateReference()
+
             self._cache.pushByStateRef(
                 stateReference, msgVersion=messageProcessingModel,
                 msgID=msgID, contextEngineId=contextEngineId,
@@ -782,10 +853,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                 reportableFlag=reportableFlag, msgMaxSize=maxMessageSize,
                 maxSizeResponseScopedPDU=maxSizeResponseScopedPDU,
                 transportDomain=transportDomain,
-                transportAddress=transportAddress
-            )
+                transportAddress=transportAddress)
 
-            debug.logger & debug.FLAG_MP and debug.logger('prepareDataElements: new stateReference %s' % stateReference)
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'prepareDataElements: new stateReference %s' % stateReference)
 
             snmpEngine.observer.storeExecutionContext(
                 snmpEngine, 'rfc3412.prepareDataElements:confirmed',
@@ -797,11 +868,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:confirmed'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:confirmed')
 
             # 7.2.13c
             return (messageProcessingModel, securityModel, securityName,
@@ -812,6 +882,7 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
 
         # 7.2.14
         if pduType in rfc3411.UNCONFIRMED_CLASS_PDUS:
+
             # Pass new stateReference to let app browse request details
             stateReference = self._cache.newStateReference()
 
@@ -825,11 +896,10 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                      contextEngineId=contextEngineId,
                      contextName=contextName,
                      securityEngineId=securityEngineId,
-                     pdu=pdu)
-            )
+                     pdu=pdu))
+
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed'
-            )
+                snmpEngine, 'rfc3412.prepareDataElements:unconfirmed')
 
             # This is not specified explicitly in RFC
             smHandler.releaseStateInformation(securityStateReference)
@@ -841,18 +911,22 @@ class SnmpV3MessageProcessingModel(AbstractMessageProcessingModel):
                     stateReference)
 
         smHandler.releaseStateInformation(securityStateReference)
-        raise error.StatusInformation(
-            errorIndication=errind.unsupportedPDUtype
-        )
 
-    def __expireEnginesInfo(self):
-        if self.__expirationTimer in self.__engineIdCacheExpQueue:
-            for engineKey in self.__engineIdCacheExpQueue[self.__expirationTimer]:
-                del self.__engineIdCache[engineKey]
-                debug.logger & debug.FLAG_MP and debug.logger('__expireEnginesInfo: expiring %r' % (engineKey,))
-            del self.__engineIdCacheExpQueue[self.__expirationTimer]
-        self.__expirationTimer += 1
+        raise error.StatusInformation(errorIndication=errind.unsupportedPDUtype)
+
+    def _expireEnginesInfo(self):
+        if self._expirationTimer in self._engineIdCacheExpQueue:
+
+            for engineKey in self._engineIdCacheExpQueue[self._expirationTimer]:
+                del self._engineIdCache[engineKey]
+
+                debug.logger & debug.FLAG_MP and debug.logger(
+                    '__expireEnginesInfo: expiring %r' % (engineKey,))
+
+            del self._engineIdCacheExpQueue[self._expirationTimer]
+
+        self._expirationTimer += 1
 
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__expireEnginesInfo()
+        self._expireEnginesInfo()
         AbstractMessageProcessingModel.receiveTimerTick(self, snmpEngine, timeNow)
diff --git a/pysnmp/proto/proxy/rfc2576.py b/pysnmp/proto/proxy/rfc2576.py
index 359a3b4f..de5a5fdb 100644
--- a/pysnmp/proto/proxy/rfc2576.py
+++ b/pysnmp/proto/proxy/rfc2576.py
@@ -102,7 +102,8 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
     pduType = v1Pdu.tagSet
     v2Pdu = V1_TO_V2_PDU_MAP[pduType].clone()
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v1ToV2: v1Pdu %s' % v1Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v1ToV2: v1Pdu %s' % v1Pdu.prettyPrint())
 
     v2VarBinds = []
 
@@ -114,21 +115,24 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
         # 3.1.2
         genericTrap = v1.apiTrapPDU.getGenericTrap(v1Pdu)
         if genericTrap == 6:
-            snmpTrapOIDParam = v1.apiTrapPDU.getEnterprise(v1Pdu) + (0, int(v1.apiTrapPDU.getSpecificTrap(v1Pdu)))
+            snmpTrapOIDParam = (v1.apiTrapPDU.getEnterprise(v1Pdu) +
+                                (0, int(v1.apiTrapPDU.getSpecificTrap(v1Pdu))))
 
         # 3.1.3
         else:
             snmpTrapOIDParam = v2c.ObjectIdentifier(V1_TO_V2_TRAP_MAP[genericTrap])
 
         # 3.1.4
-        v2VarBinds.append((v2c.apiTrapPDU.sysUpTime, sysUpTime))
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapOID, snmpTrapOIDParam))
         v2VarBinds.append(
-            (v2c.apiTrapPDU.snmpTrapAddress, v1.apiTrapPDU.getAgentAddr(v1Pdu))
-        )
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapCommunity, v2c.OctetString(snmpTrapCommunity)))
-        v2VarBinds.append((v2c.apiTrapPDU.snmpTrapEnterprise,
-                           v1.apiTrapPDU.getEnterprise(v1Pdu)))
+            (v2c.apiTrapPDU.sysUpTime, sysUpTime))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapOID, snmpTrapOIDParam))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapAddress, v1.apiTrapPDU.getAgentAddr(v1Pdu)))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapCommunity, v2c.OctetString(snmpTrapCommunity)))
+        v2VarBinds.append(
+            (v2c.apiTrapPDU.snmpTrapEnterprise, v1.apiTrapPDU.getEnterprise(v1Pdu)))
 
         varBinds = v1.apiTrapPDU.getVarBinds(v1Pdu)
 
@@ -142,13 +146,13 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
             v1Val = v1Val.getComponent()
 
         v2VarBinds.append(
-            (oid, V1_TO_V2_VALUE_MAP[v1Val.tagSet].clone(v1Val))
-        )
+            (oid, V1_TO_V2_VALUE_MAP[v1Val.tagSet].clone(v1Val)))
 
     if pduType in rfc3411.RESPONSE_CLASS_PDUS:
         # 4.1.2.2.1&2
         errorStatus = int(v1.apiPDU.getErrorStatus(v1Pdu))
         errorIndex = int(v1.apiPDU.getErrorIndex(v1Pdu, muteErrors=True))
+
         if errorStatus == 2:  # noSuchName
             if origV2Pdu.tagSet == v2c.GetNextRequestPDU.tagSet:
                 v2VarBinds = [(o, rfc1905.endOfMibView) for o, v in v2VarBinds]
@@ -171,13 +175,15 @@ def v1ToV2(v1Pdu, origV2Pdu=None, snmpTrapCommunity=''):
 
     v2c.apiPDU.setVarBinds(v2Pdu, v2VarBinds)
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v1ToV2: v2Pdu %s' % v2Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v1ToV2: v2Pdu %s' % v2Pdu.prettyPrint())
 
     return v2Pdu
 
 
 def v2ToV1(v2Pdu, origV1Pdu=None):
-    debug.logger & debug.FLAG_PRX and debug.logger('v2ToV1: v2Pdu %s' % v2Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v2ToV1: v2Pdu %s' % v2Pdu.prettyPrint())
 
     pduType = v2Pdu.tagSet
 
@@ -224,7 +230,8 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         for oid, val in v2VarBinds:
             # snmpTrapAddress
             if oid == v2c.apiTrapPDU.snmpTrapAddress:
-                v1.apiTrapPDU.setAgentAddr(v1Pdu, v1.IpAddress(val))  # v2c.OctetString is more constrained
+                # v2c.OctetString is more constrained
+                v1.apiTrapPDU.setAgentAddr(v1Pdu, v1.IpAddress(val))
                 break
 
         else:
@@ -232,7 +239,8 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
 
         # 3.2.3
         if snmpTrapOIDParam in V2_TO_V1_TRAP_MAP:
-            v1.apiTrapPDU.setGenericTrap(v1Pdu, V2_TO_V1_TRAP_MAP[snmpTrapOIDParam])
+            v1.apiTrapPDU.setGenericTrap(
+                v1Pdu, V2_TO_V1_TRAP_MAP[snmpTrapOIDParam])
 
         else:
             v1.apiTrapPDU.setGenericTrap(v1Pdu, 6)
@@ -273,6 +281,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         while idx >= 0:
             # 4.1.2.1
             oid, val = v2VarBinds[idx]
+
             if v2c.Counter64.tagSet == val.tagSet:
                 if origV1Pdu.tagSet == v1.GetRequestPDU.tagSet:
                     v1.apiPDU.setErrorStatus(v1Pdu, 2)
@@ -298,8 +307,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
         v2ErrorStatus = v2c.apiPDU.getErrorStatus(v2Pdu)
         if v2ErrorStatus:
             v1.apiPDU.setErrorStatus(
-                v1Pdu, V2_TO_V1_ERROR_MAP.get(v2ErrorStatus, 5)
-            )
+                v1Pdu, V2_TO_V1_ERROR_MAP.get(v2ErrorStatus, 5))
             v1.apiPDU.setErrorIndex(v1Pdu, v2c.apiPDU.getErrorIndex(v2Pdu, muteErrors=True))
 
     elif pduType in rfc3411.CONFIRMED_CLASS_PDUS:
@@ -309,6 +317,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
     # Translate Var-Binds
     if (pduType in rfc3411.RESPONSE_CLASS_PDUS and
             v1.apiPDU.getErrorStatus(v1Pdu)):
+
         v1VarBinds = v1.apiPDU.getVarBinds(origV1Pdu)
 
     else:
@@ -327,6 +336,7 @@ def v2ToV1(v2Pdu, origV1Pdu=None):
             v1Pdu, v2c.apiPDU.getRequestID(v2Pdu)
         )
 
-    debug.logger & debug.FLAG_PRX and debug.logger('v2ToV1: v1Pdu %s' % v1Pdu.prettyPrint())
+    debug.logger & debug.FLAG_PRX and debug.logger(
+        'v2ToV1: v1Pdu %s' % v1Pdu.prettyPrint())
 
     return v1Pdu
diff --git a/pysnmp/proto/rfc1155.py b/pysnmp/proto/rfc1155.py
index e194f1c0..f78e6dc1 100644
--- a/pysnmp/proto/rfc1155.py
+++ b/pysnmp/proto/rfc1155.py
@@ -29,15 +29,19 @@ class IpAddress(univ.OctetString):
         if isinstance(value, str) and len(value) != 4:
             try:
                 value = [int(x) for x in value.split('.')]
-            except:
+
+            except Exception:
                 raise error.ProtocolError('Bad IP address syntax %s' % value)
+
         if len(value) != 4:
             raise error.ProtocolError('Bad IP address syntax')
+
         return univ.OctetString.prettyIn(self, value)
 
     def prettyOut(self, value):
         if value:
             return '.'.join(['%d' % x for x in self.__class__(value).asNumbers()])
+
         else:
             return ''
 
@@ -70,18 +74,24 @@ class NetworkAddress(univ.Choice):
             if the type of *value* is not allowed for this Choice instance.
         """
         cloned = univ.Choice.clone(self, **kwargs)
+
         if value is not univ.noValue:
             if isinstance(value, NetworkAddress):
                 value = value.getComponent()
+
             elif not isinstance(value, IpAddress):
                 # IpAddress is the only supported type, perhaps forever because
                 # this is SNMPv1.
                 value = IpAddress(value)
+
             try:
                 tagSet = value.tagSet
+
             except AttributeError:
                 raise PyAsn1Error('component value %r has no tag set' % (value,))
+
             cloned.setComponentByType(tagSet, value)
+
         return cloned
 
     # RFC 1212, section 4.1.6:
@@ -94,17 +104,21 @@ class NetworkAddress(univ.Choice):
     def cloneFromName(self, value, impliedFlag, parentRow, parentIndices):
         kind = value[0]
         clone = self.clone()
+
         if kind == 1:
             clone['internet'] = tuple(value[1:5])
             return clone, value[5:]
+
         else:
             raise SmiError('unknown NetworkAddress type %r' % (kind,))
 
     def cloneAsName(self, impliedFlag, parentRow, parentIndices):
         kind = self.getName()
         component = self.getComponent()
+
         if kind == 'internet':
             return (1,) + tuple(component.asNumbers())
+
         else:
             raise SmiError('unknown NetworkAddress type %r' % (kind,))
 
@@ -145,7 +159,9 @@ class TypeCoercionHackMixIn:  # XXX keep this old-style class till pyasn1 types
         if componentType:
             if idx >= len(componentType):
                 raise PyAsn1Error('Component type error out of range')
+
             t = componentType[idx].getType()
+
             if not t.getTagSet().isSuperTagSetOf(value.getTagSet()):
                 raise PyAsn1Error('Component type error %r vs %r' % (t, value))
 
diff --git a/pysnmp/proto/rfc1157.py b/pysnmp/proto/rfc1157.py
index b0ddbb08..30a26bc7 100644
--- a/pysnmp/proto/rfc1157.py
+++ b/pysnmp/proto/rfc1157.py
@@ -27,8 +27,9 @@ class VarBindList(univ.SequenceOf):
 
 
 errorStatus = univ.Integer(
-    namedValues=namedval.NamedValues(('noError', 0), ('tooBig', 1), ('noSuchName', 2),
-                                     ('badValue', 3), ('readOnly', 4), ('genErr', 5)))
+    namedValues=namedval.NamedValues(
+        ('noError', 0), ('tooBig', 1), ('noSuchName', 2),
+        ('badValue', 3), ('readOnly', 4), ('genErr', 5)))
 
 
 class _RequestBase(univ.Sequence):
@@ -65,8 +66,10 @@ class SetRequestPDU(_RequestBase):
 
 
 genericTrap = univ.Integer().clone(
-    namedValues=namedval.NamedValues(('coldStart', 0), ('warmStart', 1), ('linkDown', 2), ('linkUp', 3),
-                                     ('authenticationFailure', 4), ('egpNeighborLoss', 5), ('enterpriseSpecific', 6)))
+    namedValues=namedval.NamedValues(
+        ('coldStart', 0), ('warmStart', 1), ('linkDown', 2), ('linkUp', 3),
+        ('authenticationFailure', 4), ('egpNeighborLoss', 5),
+        ('enterpriseSpecific', 6)))
 
 
 class TrapPDU(univ.Sequence):
diff --git a/pysnmp/proto/rfc1902.py b/pysnmp/proto/rfc1902.py
index e1c037ee..50252c36 100644
--- a/pysnmp/proto/rfc1902.py
+++ b/pysnmp/proto/rfc1902.py
@@ -95,7 +95,8 @@ class Integer32(univ.Integer):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.SingleValueConstraint(*values)
+            subtypeSpec = cls.subtypeSpec + constraint.SingleValueConstraint(
+                *values)
 
         X.__name__ = cls.__name__
         return X
@@ -106,7 +107,8 @@ class Integer32(univ.Integer):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.ValueRangeConstraint(minimum, maximum)
+            subtypeSpec = cls.subtypeSpec + constraint.ValueRangeConstraint(
+                minimum, maximum)
 
         X.__name__ = cls.__name__
         return X
@@ -171,6 +173,7 @@ class Integer(Integer32):
                 *values.values())
 
         X.__name__ = cls.__name__
+
         return X
 
 
@@ -234,10 +237,12 @@ class OctetString(univ.OctetString):
         return self.fixedLength
 
     def clone(self, *args, **kwargs):
-        return univ.OctetString.clone(self, *args, **kwargs).setFixedLength(self.getFixedLength())
+        return univ.OctetString.clone(
+            self, *args, **kwargs).setFixedLength(self.getFixedLength())
 
     def subtype(self, *args, **kwargs):
-        return univ.OctetString.subtype(self, *args, **kwargs).setFixedLength(self.getFixedLength())
+        return univ.OctetString.subtype(
+            self, *args, **kwargs).setFixedLength(self.getFixedLength())
 
     @classmethod
     def withSize(cls, minimum, maximum):
@@ -245,7 +250,8 @@ class OctetString(univ.OctetString):
         """
 
         class X(cls):
-            subtypeSpec = cls.subtypeSpec + constraint.ValueSizeConstraint(minimum, maximum)
+            subtypeSpec = cls.subtypeSpec + constraint.ValueSizeConstraint(
+                minimum, maximum)
 
         X.__name__ = cls.__name__
         return X
@@ -328,11 +334,15 @@ class IpAddress(OctetString):
         if isinstance(value, str) and len(value) != 4:
             try:
                 value = [int(x) for x in value.split('.')]
-            except:
+
+            except Exception:
                 raise error.ProtocolError('Bad IP address syntax %s' % value)
+
         value = OctetString.prettyIn(self, value)
+
         if len(value) != 4:
             raise error.ProtocolError('Bad IP address syntax')
+
         return value
 
     def prettyOut(self, value):
@@ -340,6 +350,7 @@ class IpAddress(OctetString):
             return '.'.join(
                 ['%d' % x for x in self.__class__(value).asNumbers()]
             )
+
         else:
             return ''
 
@@ -643,30 +654,44 @@ class Bits(OctetString):
     def prettyIn(self, bits):
         if not isinstance(bits, (tuple, list)):
             return OctetString.prettyIn(self, bits)  # raw bitstring
+
         octets = []
+
         for bit in bits:  # tuple of named bits
             v = self.namedValues.getValue(bit)
+
             if v is None:
                 raise error.ProtocolError('Unknown named bit %s' % bit)
+
             d, m = divmod(v, 8)
             if d >= len(octets):
                 octets.extend([0] * (d - len(octets) + 1))
+
             octets[d] |= 0x01 << (7 - m)
+
         return OctetString.prettyIn(self, octets)
 
     def prettyOut(self, value):
         names = []
+
         ints = self.__class__(value).asNumbers()
+
         for i, v in enumerate(ints):
             v = ints[i]
+
             j = 7
+
             while j >= 0:
                 if v & (0x01 << j):
                     name = self.namedValues.getName(i * 8 + 7 - j)
+
                     if name is None:
                         name = 'UnknownBit-%s' % (i * 8 + 7 - j,)
+
                     names.append(name)
+
                 j -= 1
+
         return ', '.join([str(x) for x in names])
 
     @classmethod
diff --git a/pysnmp/proto/rfc1905.py b/pysnmp/proto/rfc1905.py
index 6a2637e2..15f56194 100644
--- a/pysnmp/proto/rfc1905.py
+++ b/pysnmp/proto/rfc1905.py
@@ -90,11 +90,12 @@ class VarBindList(univ.SequenceOf):
 
 errorStatus = univ.Integer(
     namedValues=namedval.NamedValues(
-        ('noError', 0), ('tooBig', 1), ('noSuchName', 2), ('badValue', 3), ('readOnly', 4),
-        ('genErr', 5), ('noAccess', 6), ('wrongType', 7), ('wrongLength', 8),
-        ('wrongEncoding', 9), ('wrongValue', 10), ('noCreation', 11),
-        ('inconsistentValue', 12), ('resourceUnavailable', 13), ('commitFailed', 14),
-        ('undoFailed', 15), ('authorizationError', 16), ('notWritable', 17),
+        ('noError', 0), ('tooBig', 1), ('noSuchName', 2), ('badValue', 3),
+        ('readOnly', 4), ('genErr', 5), ('noAccess', 6), ('wrongType', 7),
+        ('wrongLength', 8), ('wrongEncoding', 9), ('wrongValue', 10),
+        ('noCreation', 11), ('inconsistentValue', 12),
+        ('resourceUnavailable', 13), ('commitFailed', 14), ('undoFailed', 15),
+        ('authorizationError', 16), ('notWritable', 17),
         ('inconsistentName', 18))
     )
 
@@ -105,13 +106,17 @@ class PDU(univ.Sequence):
         namedtype.NamedType('request-id', rfc1902.Integer32()),
         namedtype.NamedType('error-status', errorStatus),
         namedtype.NamedType('error-index',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))),
+                            univ.Integer().subtype(
+                                subtypeSpec=constraint.ValueRangeConstraint(
+                                    0, max_bindings))),
         namedtype.NamedType('variable-bindings', VarBindList())
     )
 
 
-nonRepeaters = univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
-maxRepetitions = univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
+nonRepeaters = univ.Integer().subtype(
+    subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
+maxRepetitions = univ.Integer().subtype(
+    subtypeSpec=constraint.ValueRangeConstraint(0, max_bindings))
 
 
 # Base class for bulk PDU
diff --git a/pysnmp/proto/rfc3412.py b/pysnmp/proto/rfc3412.py
index 7a3baa86..4e0f401c 100644
--- a/pysnmp/proto/rfc3412.py
+++ b/pysnmp/proto/rfc3412.py
@@ -28,6 +28,7 @@ class MsgAndPduDispatcher(object):
             self.mibInstrumController = instrum.MibInstrumController(
                 builder.MibBuilder()
             )
+
         else:
             self.mibInstrumController = mibInstrumController
 
@@ -37,25 +38,25 @@ class MsgAndPduDispatcher(object):
         )
 
         # Requests cache
-        self.__cache = cache.Cache()
+        self._cache = cache.Cache()
 
         # Registered context engine IDs
-        self.__appsRegistration = {}
+        self._appsRegistration = {}
 
         # Source of sendPduHandle and cache of requesting apps
-        self.__sendPduHandle = nextid.Integer(0xffffff)
+        self._sendPduHandle = nextid.Integer(0xffffff)
 
         # To pass transport info to app (legacy)
-        self.__transportInfo = {}
+        self._transportInfo = {}
 
     # legacy
     def getTransportInfo(self, stateReference):
-        if stateReference in self.__transportInfo:
-            return self.__transportInfo[stateReference]
+        if stateReference in self._transportInfo:
+            return self._transportInfo[stateReference]
+
         else:
             raise error.ProtocolError(
-                'No data for stateReference %s' % stateReference
-            )
+                'No data for stateReference %s' % stateReference)
 
     # Application registration with dispatcher
 
@@ -66,42 +67,45 @@ class MsgAndPduDispatcher(object):
 
         # 4.3.3
         for pduType in pduTypes:
-            k = (contextEngineId, pduType)
-            if k in self.__appsRegistration:
+            k = contextEngineId, pduType
+            if k in self._appsRegistration:
                 raise error.ProtocolError(
-                    'Duplicate registration %r/%s' % (contextEngineId, pduType)
-                )
+                    'Duplicate registration %r/%s' % (contextEngineId, pduType))
 
             # 4.3.4
-            self.__appsRegistration[k] = processPdu
+            self._appsRegistration[k] = processPdu
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'registerContextEngineId: contextEngineId %r pduTypes %s' % (contextEngineId, pduTypes))
+            'registerContextEngineId: contextEngineId %r pduTypes '
+            '%s' % (contextEngineId, pduTypes))
 
     # 4.4.1
     def unregisterContextEngineId(self, contextEngineId, pduTypes):
         """Unregister application with dispatcher"""
+
         # 4.3.4
         if contextEngineId is None:
             # Default to local snmpEngineId
-            contextEngineId, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                  'snmpEngineID')
+            contextEngineId, = self.mibInstrumController.mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
         for pduType in pduTypes:
-            k = (contextEngineId, pduType)
-            if k in self.__appsRegistration:
-                del self.__appsRegistration[k]
+            k = contextEngineId, pduType
+            if k in self._appsRegistration:
+                del self._appsRegistration[k]
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'unregisterContextEngineId: contextEngineId %r pduTypes %s' % (contextEngineId, pduTypes))
+            'unregisterContextEngineId: contextEngineId %r pduTypes '
+            '%s' % (contextEngineId, pduTypes))
 
     def getRegisteredApp(self, contextEngineId, pduType):
-        k = (contextEngineId, pduType)
-        if k in self.__appsRegistration:
-            return self.__appsRegistration[k]
-        k = (null, pduType)
-        if k in self.__appsRegistration:
-            return self.__appsRegistration[k]  # wildcard
+        k = contextEngineId, pduType
+        if k in self._appsRegistration:
+            return self._appsRegistration[k]
+
+        k = null, pduType
+        if k in self._appsRegistration:
+            return self._appsRegistration[k]  # wildcard
 
     # Dispatcher <-> application API
 
@@ -115,20 +119,23 @@ class MsgAndPduDispatcher(object):
         """PDU dispatcher -- prepare and serialize a request or notification"""
         # 4.1.1.2
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedMsgProcessingModel
-            )
+                errorIndication=errind.unsupportedMsgProcessingModel)
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'sendPdu: securityName %s, PDU\n%s' % (securityName, PDU.prettyPrint()))
+            'sendPdu: securityName %s, PDU\n'
+            '%s' % (securityName, PDU.prettyPrint()))
 
         # 4.1.1.3
-        sendPduHandle = self.__sendPduHandle()
+        sendPduHandle = self._sendPduHandle()
+
         if expectResponse:
-            self.__cache.add(
+            self._cache.add(
                 sendPduHandle,
                 messageProcessingModel=messageProcessingModel,
                 sendPduHandle=sendPduHandle,
@@ -137,11 +144,14 @@ class MsgAndPduDispatcher(object):
                 cbCtx=cbCtx
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('sendPdu: current time %d ticks, one tick is %s seconds' % (
-                snmpEngine.transportDispatcher.getTimerTicks(), snmpEngine.transportDispatcher.getTimerResolution()))
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'sendPdu: current time %d ticks, one tick is %s '
+                'seconds' % (snmpEngine.transportDispatcher.getTimerTicks(),
+                             snmpEngine.transportDispatcher.getTimerResolution()))
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'sendPdu: new sendPduHandle %s, timeout %s ticks, cbFun %s' % (sendPduHandle, timeout, cbFun))
+            'sendPdu: new sendPduHandle %s, timeout %s ticks, cbFun '
+            '%s' % (sendPduHandle, timeout, cbFun))
 
         origTransportDomain = transportDomain
         origTransportAddress = transportAddress
@@ -157,17 +167,20 @@ class MsgAndPduDispatcher(object):
                 pduVersion, PDU, expectResponse, sendPduHandle
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('sendPdu: MP succeeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'sendPdu: MP succeeded')
+
         except PySnmpError:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
                 self.releaseStateInformation(snmpEngine, sendPduHandle, messageProcessingModel)
+
             raise
 
         # 4.1.1.6
         if snmpEngine.transportDispatcher is None:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
 
             raise error.PySnmpError('Transport dispatcher not set')
 
@@ -187,27 +200,30 @@ class MsgAndPduDispatcher(object):
 
         try:
             snmpEngine.transportDispatcher.sendMessage(
-                outgoingMessage, transportDomain, transportAddress
-            )
+                outgoingMessage, transportDomain, transportAddress)
+
         except PySnmpError:
             if expectResponse:
-                self.__cache.pop(sendPduHandle)
+                self._cache.pop(sendPduHandle)
             raise
 
-        snmpEngine.observer.clearExecutionContext(snmpEngine, 'rfc3412.sendPdu')
+        snmpEngine.observer.clearExecutionContext(
+            snmpEngine, 'rfc3412.sendPdu')
 
         # Update cache with orignal req params (used for retrying)
         if expectResponse:
-            self.__cache.update(sendPduHandle,
-                                transportDomain=origTransportDomain,
-                                transportAddress=origTransportAddress,
-                                securityModel=securityModel,
-                                securityName=securityName,
-                                securityLevel=securityLevel,
-                                contextEngineId=contextEngineId,
-                                contextName=contextName,
-                                pduVersion=pduVersion,
-                                PDU=PDU)
+            self._cache.update(
+                sendPduHandle,
+                transportDomain=origTransportDomain,
+                transportAddress=origTransportAddress,
+                securityModel=securityModel,
+                securityName=securityName,
+                securityLevel=securityLevel,
+                contextEngineId=contextEngineId,
+                contextName=contextName,
+                pduVersion=pduVersion,
+                PDU=PDU
+            )
 
         return sendPduHandle
 
@@ -217,17 +233,20 @@ class MsgAndPduDispatcher(object):
                           contextEngineId, contextName, pduVersion,
                           PDU, maxSizeResponseScopedPDU, stateReference,
                           statusInformation):
+
         # Extract input values and initialize defaults
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedMsgProcessingModel
-            )
+                errorIndication=errind.unsupportedMsgProcessingModel)
 
         debug.logger & debug.FLAG_DSP and debug.logger(
-            'returnResponsePdu: PDU %s' % (PDU and PDU.prettyPrint() or "<empty>",))
+            'returnResponsePdu: PDU '
+            '%s' % (PDU and PDU.prettyPrint() or "<empty>",))
 
         # 4.1.2.2
         try:
@@ -240,19 +259,26 @@ class MsgAndPduDispatcher(object):
                 statusInformation
             )
 
-            debug.logger & debug.FLAG_DSP and debug.logger('returnResponsePdu: MP suceeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'returnResponsePdu: MP suceeded')
 
         except error.StatusInformation:
             # 4.1.2.3
             raise
 
+        mibBuilder = self.mibInstrumController.mibBuilder
+
         # Handle oversized messages XXX transport constrains?
-        snmpEngineMaxMessageSize, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                       'snmpEngineMaxMessageSize')
+        snmpEngineMaxMessageSize, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineMaxMessageSize')
+
         if (snmpEngineMaxMessageSize.syntax and
                 len(outgoingMessage) > snmpEngineMaxMessageSize.syntax):
-            snmpSilentDrops, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpSilentDrops')
+
+            snmpSilentDrops, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpSilentDrops')
             snmpSilentDrops.syntax += 1
+
             raise error.StatusInformation(errorIndication=errind.tooBig)
 
         snmpEngine.observer.storeExecutionContext(
@@ -271,45 +297,50 @@ class MsgAndPduDispatcher(object):
         )
 
         # 4.1.2.4
-        snmpEngine.transportDispatcher.sendMessage(outgoingMessage,
-                                                   transportDomain,
-                                                   transportAddress)
+        snmpEngine.transportDispatcher.sendMessage(
+            outgoingMessage, transportDomain, transportAddress)
 
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3412.returnResponsePdu'
-        )
+            snmpEngine, 'rfc3412.returnResponsePdu')
 
     # 4.2.1
     def receiveMessage(self, snmpEngine, transportDomain,
                        transportAddress, wholeMsg):
         """Message dispatcher -- de-serialize message into PDU"""
+        mibBuilder = self.mibInstrumController.mibBuilder
+
         # 4.2.1.1
-        snmpInPkts, = self.mibInstrumController.mibBuilder.importSymbols(
-            '__SNMPv2-MIB', 'snmpInPkts'
-        )
+        snmpInPkts, = mibBuilder.importSymbols(
+            '__SNMPv2-MIB', 'snmpInPkts')
         snmpInPkts.syntax += 1
 
+        restOfWholeMsg = null  # XXX fix decoder non-recursive return
+
         # 4.2.1.2
         try:
-            restOfWholeMsg = null  # XXX fix decoder non-recursive return
             msgVersion = verdec.decodeMessageVersion(wholeMsg)
 
         except error.ProtocolError:
-            snmpInASNParseErrs, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB',
-                                                                                     'snmpInASNParseErrs')
+            snmpInASNParseErrs, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInASNParseErrs')
             snmpInASNParseErrs.syntax += 1
+
             return null  # n.b the whole buffer gets dropped
 
-        debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: msgVersion %s, msg decoded' % msgVersion)
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            'receiveMessage: msgVersion %s, msg decoded' % msgVersion)
 
         messageProcessingModel = msgVersion
 
         try:
-            mpHandler = snmpEngine.messageProcessingSubsystems[int(messageProcessingModel)]
+            mpHandler = snmpEngine.messageProcessingSubsystems[
+                int(messageProcessingModel)]
 
         except KeyError:
-            snmpInBadVersions, = self.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInBadVersions')
+            snmpInBadVersions, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInBadVersions')
             snmpInBadVersions.syntax += 1
+
             return restOfWholeMsg
 
         # 4.2.1.3 -- no-op
@@ -329,48 +360,56 @@ class MsgAndPduDispatcher(object):
              maxSizeResponseScopedPDU,
              statusInformation,
              stateReference) = mpHandler.prepareDataElements(
-                snmpEngine, transportDomain, transportAddress, wholeMsg
-            )
+                snmpEngine, transportDomain, transportAddress, wholeMsg)
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: MP succeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: MP succeded')
 
         except error.StatusInformation as exc:
             statusInformation = exc
+
             if 'sendPduHandle' in statusInformation:
                 # Dropped REPORT -- re-run pending reqs queue as some
                 # of them may be waiting for this REPORT
                 debug.logger & debug.FLAG_DSP and debug.logger(
-                    'receiveMessage: MP failed, statusInformation %s, forcing a retry' % statusInformation)
+                    'receiveMessage: MP failed, statusInformation %s, '
+                    'forcing retry' % statusInformation)
+
                 self.__expireRequest(
                     statusInformation['sendPduHandle'],
-                    self.__cache.pop(statusInformation['sendPduHandle']),
+                    self._cache.pop(statusInformation['sendPduHandle']),
                     snmpEngine,
-                    statusInformation
-                )
+                    statusInformation)
+
             return restOfWholeMsg
 
         except PyAsn1Error as exc:
-            debug.logger & debug.FLAG_MP and debug.logger('receiveMessage: %s' % exc)
-            snmpInASNParseErrs, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInASNParseErrs')
+            debug.logger & debug.FLAG_MP and debug.logger(
+                'receiveMessage: %s' % exc)
+            snmpInASNParseErrs, = mibBuilder.importSymbols(
+                '__SNMPv2-MIB', 'snmpInASNParseErrs')
             snmpInASNParseErrs.syntax += 1
 
             return restOfWholeMsg
 
-        debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: PDU %s' % PDU.prettyPrint())
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            'receiveMessage: PDU %s' % PDU.prettyPrint())
 
         # 4.2.2
         if sendPduHandle is None:
             # 4.2.2.1 (request or notification)
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: pduType %s' % pduType)
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: pduType %s' % pduType)
+
             # 4.2.2.1.1
             processPdu = self.getRegisteredApp(contextEngineId, pduType)
 
             # 4.2.2.1.2
             if processPdu is None:
                 # 4.2.2.1.2.a
-                snmpUnknownPDUHandlers, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB',
-                                                                                             'snmpUnknownPDUHandlers')
+                snmpUnknownPDUHandlers, = importSymbols(
+                    '__SNMP-MPD-MIB', 'snmpUnknownPDUHandlers')
                 snmpUnknownPDUHandlers.syntax += 1
 
                 # 4.2.2.1.2.b
@@ -380,7 +419,8 @@ class MsgAndPduDispatcher(object):
                     'val': snmpUnknownPDUHandlers.syntax
                 }
 
-                debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: unhandled PDU type')
+                debug.logger & debug.FLAG_DSP and debug.logger(
+                    'receiveMessage: unhandled PDU type')
 
                 # 4.2.2.1.2.c
                 try:
@@ -391,20 +431,19 @@ class MsgAndPduDispatcher(object):
                         securityModel, securityName, securityLevel,
                         contextEngineId, contextName, pduVersion,
                         PDU, maxSizeResponseScopedPDU, stateReference,
-                        statusInformation
-                    )
+                        statusInformation)
 
                     snmpEngine.transportDispatcher.sendMessage(
                         outgoingMessage, destTransportDomain,
-                        destTransportAddress
-                    )
+                        destTransportAddress)
 
                 except PySnmpError as exc:
                     debug.logger & debug.FLAG_DSP and debug.logger(
                         'receiveMessage: report failed, statusInformation %s' % exc)
 
                 else:
-                    debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: reporting succeeded')
+                    debug.logger & debug.FLAG_DSP and debug.logger(
+                        'receiveMessage: reporting succeeded')
 
                 # 4.2.2.1.2.d
                 return restOfWholeMsg
@@ -421,42 +460,44 @@ class MsgAndPduDispatcher(object):
                          securityLevel=securityLevel,
                          contextEngineId=contextEngineId,
                          contextName=contextName,
-                         pdu=PDU)
-                )
+                         pdu=PDU))
 
                 # pass transport info to app (legacy)
                 if stateReference is not None:
-                    self.__transportInfo[stateReference] = (
-                        transportDomain, transportAddress
-                    )
+                    self._transportInfo[stateReference] = (
+                        transportDomain, transportAddress)
 
                 # 4.2.2.1.3 (asynchronous function)
-                processPdu(snmpEngine, messageProcessingModel,
-                           securityModel, securityName, securityLevel,
-                           contextEngineId, contextName, pduVersion,
-                           PDU, maxSizeResponseScopedPDU, stateReference)
+                processPdu(
+                    snmpEngine, messageProcessingModel, securityModel,
+                    securityName, securityLevel, contextEngineId,
+                    contextName, pduVersion, PDU, maxSizeResponseScopedPDU,
+                    stateReference)
 
                 snmpEngine.observer.clearExecutionContext(
-                    snmpEngine, 'rfc3412.receiveMessage:request'
-                )
+                    snmpEngine, 'rfc3412.receiveMessage:request')
 
                 # legacy
                 if stateReference is not None:
-                    del self.__transportInfo[stateReference]
+                    del self._transportInfo[stateReference]
+
+                debug.logger & debug.FLAG_DSP and debug.logger(
+                    'receiveMessage: processPdu initiated')
 
-                debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: processPdu initiated')
                 return restOfWholeMsg
+
         else:
             # 4.2.2.2 (response)
 
             # 4.2.2.2.1
-            cachedParams = self.__cache.pop(sendPduHandle)
+            cachedParams = self._cache.pop(sendPduHandle)
 
             # 4.2.2.2.2
             if cachedParams is None:
-                snmpUnknownPDUHandlers, = self.mibInstrumController.mibBuilder.importSymbols('__SNMP-MPD-MIB',
-                                                                                             'snmpUnknownPDUHandlers')
+                snmpUnknownPDUHandlers, = mibBuilder.importSymbols(
+                    '__SNMP-MPD-MIB', 'snmpUnknownPDUHandlers')
                 snmpUnknownPDUHandlers.syntax += 1
+
                 return restOfWholeMsg
 
             debug.logger & debug.FLAG_DSP and debug.logger(
@@ -476,42 +517,44 @@ class MsgAndPduDispatcher(object):
                      securityLevel=securityLevel,
                      contextEngineId=contextEngineId,
                      contextName=contextName,
-                     pdu=PDU)
-            )
+                     pdu=PDU))
 
             # 4.2.2.2.4
             processResponsePdu = cachedParams['cbFun']
 
-            processResponsePdu(snmpEngine, messageProcessingModel,
-                               securityModel, securityName, securityLevel,
-                               contextEngineId, contextName, pduVersion,
-                               PDU, statusInformation,
-                               cachedParams['sendPduHandle'],
-                               cachedParams['cbCtx'])
+            processResponsePdu(
+                snmpEngine, messageProcessingModel, securityModel,
+                securityName, securityLevel, contextEngineId, contextName,
+                pduVersion, PDU, statusInformation,
+                cachedParams['sendPduHandle'],
+                cachedParams['cbCtx'])
 
             snmpEngine.observer.clearExecutionContext(
-                snmpEngine, 'rfc3412.receiveMessage:response'
-            )
+                snmpEngine, 'rfc3412.receiveMessage:response')
 
-            debug.logger & debug.FLAG_DSP and debug.logger('receiveMessage: processResponsePdu succeeded')
+            debug.logger & debug.FLAG_DSP and debug.logger(
+                'receiveMessage: processResponsePdu succeeded')
 
             return restOfWholeMsg
 
     def releaseStateInformation(self, snmpEngine, sendPduHandle,
                                 messageProcessingModel):
         k = int(messageProcessingModel)
+
         if k in snmpEngine.messageProcessingSubsystems:
             mpHandler = snmpEngine.messageProcessingSubsystems[k]
             mpHandler.releaseStateInformation(sendPduHandle)
 
-        self.__cache.pop(sendPduHandle)
+        self._cache.pop(sendPduHandle)
 
     # Cache expiration stuff
 
     # noinspection PyUnusedLocal
     def __expireRequest(self, cacheKey, cachedParams, snmpEngine,
                         statusInformation=None):
+
         timeNow = snmpEngine.transportDispatcher.getTimerTicks()
+
         timeoutAt = cachedParams['timeout']
 
         if statusInformation is None and timeNow < timeoutAt:
@@ -519,24 +562,25 @@ class MsgAndPduDispatcher(object):
 
         processResponsePdu = cachedParams['cbFun']
 
-        debug.logger & debug.FLAG_DSP and debug.logger('__expireRequest: req cachedParams %s' % cachedParams)
+        debug.logger & debug.FLAG_DSP and debug.logger(
+            '__expireRequest: req cachedParams %s' % cachedParams)
 
         # Fail timed-out requests
         if not statusInformation:
             statusInformation = error.StatusInformation(
-                errorIndication=errind.requestTimedOut
-            )
+                errorIndication=errind.requestTimedOut)
+
+        self.releaseStateInformation(
+            snmpEngine, cachedParams['sendPduHandle'],
+            cachedParams['messageProcessingModel'])
 
-        self.releaseStateInformation(snmpEngine,
-                                     cachedParams['sendPduHandle'],
-                                     cachedParams['messageProcessingModel'])
+        processResponsePdu(
+            snmpEngine, None, None, None, None, None, None, None, None,
+            statusInformation,
+            cachedParams['sendPduHandle'], cachedParams['cbCtx'])
 
-        processResponsePdu(snmpEngine, None, None, None, None, None,
-                           None, None, None, statusInformation,
-                           cachedParams['sendPduHandle'],
-                           cachedParams['cbCtx'])
         return True
 
     # noinspection PyUnusedLocal
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__cache.expire(self.__expireRequest, snmpEngine)
+        self._cache.expire(self.__expireRequest, snmpEngine)
diff --git a/pysnmp/proto/secmod/cache.py b/pysnmp/proto/secmod/cache.py
index f5843c50..1859bbad 100644
--- a/pysnmp/proto/secmod/cache.py
+++ b/pysnmp/proto/secmod/cache.py
@@ -21,10 +21,8 @@ class Cache(object):
 
     def pop(self, stateReference):
         if stateReference in self.__cacheEntries:
-            securityData = self.__cacheEntries[stateReference]
-        else:
-            raise error.ProtocolError(
-                'Cache miss for stateReference=%s at %s' % (stateReference, self)
-            )
-        del self.__cacheEntries[stateReference]
-        return securityData
+            return self.__cacheEntries.pop(stateReference)
+
+        raise error.ProtocolError(
+            'Cache miss for stateReference=%s at '
+            '%s' % (stateReference, self))
diff --git a/pysnmp/proto/secmod/eso/priv/aes192.py b/pysnmp/proto/secmod/eso/priv/aes192.py
index 7df0a0f5..cbbc748e 100644
--- a/pysnmp/proto/secmod/eso/priv/aes192.py
+++ b/pysnmp/proto/secmod/eso/priv/aes192.py
@@ -14,7 +14,8 @@ class AesBlumenthal192(aesbase.AbstractAesBlumenthal):
 
        http://tools.ietf.org/html/draft-blumenthal-aes-usm-04
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 1)  # cusmAESCfb192PrivProtocol
+    # cusmAESCfb192PrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 1)
     KEY_SIZE = 24
 
 
@@ -29,5 +30,6 @@ class Aes192(aesbase.AbstractAesReeder):
 
     Known to be used by many vendors including Cisco and others.
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 101)  # cusmAESCfb192PrivProtocol (non-standard OID)
+    # cusmAESCfb192PrivProtocol (non-standard OID)
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 101)
     KEY_SIZE = 24
diff --git a/pysnmp/proto/secmod/eso/priv/aes256.py b/pysnmp/proto/secmod/eso/priv/aes256.py
index 94a255ff..7ca42504 100644
--- a/pysnmp/proto/secmod/eso/priv/aes256.py
+++ b/pysnmp/proto/secmod/eso/priv/aes256.py
@@ -12,7 +12,8 @@ class AesBlumenthal256(aesbase.AbstractAesBlumenthal):
 
        http://tools.ietf.org/html/draft-blumenthal-aes-usm-04
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 2)  # cusmAESCfb256PrivProtocol
+    # cusmAESCfb256PrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 2)
     KEY_SIZE = 32
 
 
@@ -27,5 +28,6 @@ class Aes256(aesbase.AbstractAesReeder):
 
     Known to be used by many vendors including Cisco and others.
     """
-    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 102)  # cusmAESCfb256PrivProtocol (non-standard OID)
+    # cusmAESCfb256PrivProtocol (non-standard OID)
+    SERVICE_ID = (1, 3, 6, 1, 4, 1, 9, 12, 6, 1, 102)
     KEY_SIZE = 32
diff --git a/pysnmp/proto/secmod/eso/priv/aesbase.py b/pysnmp/proto/secmod/eso/priv/aesbase.py
index 0c2e5d17..3af30df0 100644
--- a/pysnmp/proto/secmod/eso/priv/aesbase.py
+++ b/pysnmp/proto/secmod/eso/priv/aesbase.py
@@ -24,19 +24,25 @@ class AbstractAesBlumenthal(aes.Aes):
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
 
-        localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+        localPrivKey = localkey.localizeKey(
+            privKey, snmpEngineID, hashAlgo)
 
-        # now extend this key if too short by repeating steps that includes the hashPassphrase step
-        for count in range(1, int(ceil(self.KEY_SIZE * 1.0 / len(localPrivKey)))):
+        # now extend this key if too short by repeating steps that includes
+        # the hashPassphrase step
+        rounds = int(ceil(self.KEY_SIZE * 1.0 / len(localPrivKey)))
+
+        for _ in range(1, rounds):
             localPrivKey += hashAlgo(localPrivKey).digest()
 
         return localPrivKey[:self.KEY_SIZE]
@@ -64,14 +70,16 @@ class AbstractAesReeder(aes.Aes):
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
 
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
 
diff --git a/pysnmp/proto/secmod/eso/priv/des3.py b/pysnmp/proto/secmod/eso/priv/des3.py
index da84475b..8d193084 100644
--- a/pysnmp/proto/secmod/eso/priv/des3.py
+++ b/pysnmp/proto/secmod/eso/priv/des3.py
@@ -34,7 +34,8 @@ class Des3(base.AbstractEncryptionService):
 
        https://tools.ietf.org/html/draft-reeder-snmpv3-usm-3desede-00
     """
-    SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3)  # usm3DESEDEPrivProtocol
+    # usm3DESEDEPrivProtocol
+    SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 2, 3)
     KEY_SIZE = 32
 
     local_int = random.randrange(0, 0xffffffff)
@@ -42,28 +43,34 @@ class Des3(base.AbstractEncryptionService):
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     # 2.1
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
 
         # now extend this key if too short by repeating steps that includes the hashPassphrase step
@@ -75,7 +82,7 @@ class Des3(base.AbstractEncryptionService):
         return localPrivKey[:self.KEY_SIZE]
 
     # 5.1.1.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots):
+    def _getEncryptionKey(self, privKey, snmpEngineBoots):
         # 5.1.1.1.1
         des3Key = privKey[:24]
         preIV = privKey[24:32]
@@ -94,39 +101,46 @@ class Des3(base.AbstractEncryptionService):
         ]
         if self.local_int == 0xffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
         # salt not yet hashed XXX
 
+        iv = map(lambda x, y: x ^ y, salt, preIV.asNumbers())
+
         return (des3Key.asOctets(),
                 univ.OctetString(salt).asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     @staticmethod
-    def __getDecryptionKey(privKey, salt):
+    def _getDecryptionKey(privKey, salt):
+        iv = map(
+            lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())
+
         return (privKey[:24].asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[24:32].asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     # 5.1.1.2
     def encryptData(self, encryptKey, privParameters, dataToEncrypt):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
-        des3Key, salt, iv = self.__getEncryptionKey(
+        des3Key, salt, iv = self._getEncryptionKey(
             encryptKey, snmpEngineBoots
         )
 
         privParameters = univ.OctetString(salt)
 
-        plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
+        plaintext = dataToEncrypt
+        plaintext += univ.OctetString(
+            (0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
 
         try:
             ciphertext = des3.encrypt(plaintext, des3Key, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         return univ.OctetString(ciphertext), privParameters
 
@@ -136,15 +150,13 @@ class Des3(base.AbstractEncryptionService):
 
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
-        des3Key, iv = self.__getDecryptionKey(decryptKey, salt)
+        des3Key, iv = self._getDecryptionKey(decryptKey, salt)
 
         if len(encryptedData) % 8 != 0:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         ciphertext = encryptedData.asOctets()
 
@@ -153,7 +165,6 @@ class Des3(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         return plaintext
diff --git a/pysnmp/proto/secmod/rfc2576.py b/pysnmp/proto/secmod/rfc2576.py
index ba11b0fe..92b5eac2 100644
--- a/pysnmp/proto/secmod/rfc2576.py
+++ b/pysnmp/proto/secmod/rfc2576.py
@@ -4,9 +4,6 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-from pyasn1.codec.ber import encoder
-from pyasn1.error import PyAsn1Error
-
 from pysnmp import debug
 from pysnmp.carrier.asyncore.dgram import udp
 from pysnmp.carrier.asyncore.dgram import udp6
@@ -15,6 +12,9 @@ from pysnmp.proto import error
 from pysnmp.proto.secmod import base
 from pysnmp.smi.error import NoSuchInstanceError
 
+from pyasn1.codec.ber import encoder
+from pyasn1.error import PyAsn1Error
+
 
 class SnmpV1SecurityModel(base.AbstractSecurityModel):
     SECURITY_MODEL_ID = 1
@@ -26,60 +26,69 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
     # in here.
 
     def __init__(self):
-        self.__transportBranchId = self.__paramsBranchId = self.__communityBranchId = self.__securityBranchId = -1
+        self._transportBranchId = -1
+        self._paramsBranchId = -1
+        self._communityBranchId = -1
+        self._securityBranchId = -1
+
         base.AbstractSecurityModel.__init__(self)
 
     def _sec2com(self, snmpEngine, securityName, contextEngineId, contextName):
-        snmpTargetParamsSecurityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpTargetParamsSecurityName, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityName')
-        if self.__paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
-            snmpTargetParamsSecurityModel, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+
+        if self._paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
+            snmpTargetParamsSecurityModel, = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityModel')
 
-            self.__nameToModelMap = {}
+            self._nameToModelMap = {}
 
             nextMibNode = snmpTargetParamsSecurityName
 
             while True:
                 try:
-                    nextMibNode = snmpTargetParamsSecurityName.getNextNode(nextMibNode.name)
+                    nextMibNode = snmpTargetParamsSecurityName.getNextNode(
+                        nextMibNode.name)
 
                 except NoSuchInstanceError:
                     break
 
                 instId = nextMibNode.name[len(snmpTargetParamsSecurityName.name):]
 
-                mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
+                mibNode = snmpTargetParamsSecurityModel.getNode(
+                    snmpTargetParamsSecurityModel.name + instId)
 
                 try:
-                    if mibNode.syntax not in self.__nameToModelMap:
-                        self.__nameToModelMap[nextMibNode.syntax] = set()
+                    if mibNode.syntax not in self._nameToModelMap:
+                        self._nameToModelMap[nextMibNode.syntax] = set()
 
-                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                    self._nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2com: table entries %r/%r hashing failed' % (
-                            nextMibNode.syntax, mibNode.syntax)
-                    )
+                        '_sec2com: table entries %r/%r hashing '
+                        'failed' % (nextMibNode.syntax, mibNode.syntax))
                     continue
 
-            self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
+            self._paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
             # invalidate next map as it include this one
-            self.__securityBranchId = -1
+            self._securityBranchId = -1
 
-        snmpCommunityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMP-COMMUNITY-MIB',
-                                                                                                   'snmpCommunityName')
-        if self.__securityBranchId != snmpCommunityName.branchVersionId:
+        snmpCommunityName, = mibBuilder.importSymbols(
+            'SNMP-COMMUNITY-MIB', 'snmpCommunityName')
+
+        if self._securityBranchId != snmpCommunityName.branchVersionId:
             (snmpCommunitySecurityName,
              snmpCommunityContextEngineId,
-             snmpCommunityContextName) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpCommunityContextName) = mibBuilder.importSymbols(
                 'SNMP-COMMUNITY-MIB', 'snmpCommunitySecurityName',
                 'snmpCommunityContextEngineID', 'snmpCommunityContextName'
             )
 
-            self.__securityMap = {}
+            self._securityMap = {}
 
             nextMibNode = snmpCommunityName
 
@@ -92,54 +101,55 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpCommunityName.name):]
 
-                _securityName = snmpCommunitySecurityName.getNode(snmpCommunitySecurityName.name + instId).syntax
+                _securityName = snmpCommunitySecurityName.getNode(
+                    snmpCommunitySecurityName.name + instId).syntax
 
                 _contextEngineId = snmpCommunityContextEngineId.getNode(
                     snmpCommunityContextEngineId.name + instId).syntax
 
-                _contextName = snmpCommunityContextName.getNode(snmpCommunityContextName.name + instId).syntax
+                _contextName = snmpCommunityContextName.getNode(
+                    snmpCommunityContextName.name + instId).syntax
+
+                key = _securityName, _contextEngineId, _contextName
 
                 try:
-                    self.__securityMap[(_securityName,
-                                        _contextEngineId,
-                                        _contextName)] = nextMibNode.syntax
+                    self._securityMap[key] = nextMibNode.syntax
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2com: table entries %r/%r/%r hashing failed' % (
-                            _securityName, _contextEngineId, _contextName)
-                    )
+                        '_sec2com: table entries %r/%r/%r hashing failed' % key)
                     continue
 
-            self.__securityBranchId = snmpCommunityName.branchVersionId
+            self._securityBranchId = snmpCommunityName.branchVersionId
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_sec2com: built securityName to communityName map, version %s: %s' % (
-                    self.__securityBranchId, self.__securityMap))
+                '_sec2com: built securityName to communityName map, version '
+                '%s: %s' % (self._securityBranchId, self._securityMap))
+
+        key = securityName, contextEngineId, contextName
 
         try:
-            return self.__securityMap[(securityName,
-                                       contextEngineId,
-                                       contextName)]
+            return self._securityMap[key]
 
         except KeyError:
             raise error.StatusInformation(
-                errorIndication=errind.unknownCommunityName
-            )
+                errorIndication=errind.unknownCommunityName)
 
     def _com2sec(self, snmpEngine, communityName, transportInformation):
-        snmpTargetAddrTAddress, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
+        snmpTargetAddrTAddress, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetAddrTAddress')
-        if self.__transportBranchId != snmpTargetAddrTAddress.branchVersionId:
+
+        if self._transportBranchId != snmpTargetAddrTAddress.branchVersionId:
             (SnmpTagValue, snmpTargetAddrTDomain,
-             snmpTargetAddrTagList) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpTargetAddrTagList) = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'SnmpTagValue', 'snmpTargetAddrTDomain',
-                'snmpTargetAddrTagList'
-            )
+                'snmpTargetAddrTagList')
 
-            self.__emptyTag = SnmpTagValue('')
+            self._emptyTag = SnmpTagValue('')
 
-            self.__transportToTagMap = {}
+            self._transportToTagMap = {}
 
             nextMibNode = snmpTargetAddrTagList
 
@@ -151,56 +161,64 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                     break
 
                 instId = nextMibNode.name[len(snmpTargetAddrTagList.name):]
-                targetAddrTDomain = snmpTargetAddrTDomain.getNode(snmpTargetAddrTDomain.name + instId).syntax
-                targetAddrTAddress = snmpTargetAddrTAddress.getNode(snmpTargetAddrTAddress.name + instId).syntax
+
+                targetAddrTDomain = snmpTargetAddrTDomain.getNode(
+                    snmpTargetAddrTDomain.name + instId).syntax
+                targetAddrTAddress = snmpTargetAddrTAddress.getNode(
+                    snmpTargetAddrTAddress.name + instId).syntax
 
                 targetAddrTDomain = tuple(targetAddrTDomain)
 
-                if targetAddrTDomain[:len(udp.SNMP_UDP_DOMAIN)] == udp.SNMP_UDP_DOMAIN:
-                    SnmpUDPAddress, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMPv2-TM',
-                                                                                                            'SnmpUDPAddress')
+                if (targetAddrTDomain[:len(udp.SNMP_UDP_DOMAIN)] ==
+                        udp.SNMP_UDP_DOMAIN):
+                    SnmpUDPAddress, = mibBuilder.importSymbols(
+                        'SNMPv2-TM', 'SnmpUDPAddress')
                     targetAddrTAddress = tuple(SnmpUDPAddress(targetAddrTAddress))
-                elif targetAddrTDomain[:len(udp6.SNMP_UDP6_DOMAIN)] == udp6.SNMP_UDP6_DOMAIN:
-                    TransportAddressIPv6, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+
+                elif (targetAddrTDomain[:len(udp6.SNMP_UDP6_DOMAIN)] ==
+                        udp6.SNMP_UDP6_DOMAIN):
+                    TransportAddressIPv6, = mibBuilder.importSymbols(
                         'TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
+
                     targetAddrTAddress = tuple(TransportAddressIPv6(targetAddrTAddress))
 
                 targetAddr = targetAddrTDomain, targetAddrTAddress
-                targetAddrTagList = snmpTargetAddrTagList.getNode(snmpTargetAddrTagList.name + instId).syntax
 
-                if targetAddr not in self.__transportToTagMap:
-                    self.__transportToTagMap[targetAddr] = set()
+                targetAddrTagList = snmpTargetAddrTagList.getNode(
+                    snmpTargetAddrTagList.name + instId).syntax
+
+                if targetAddr not in self._transportToTagMap:
+                    self._transportToTagMap[targetAddr] = set()
 
                 try:
                     if targetAddrTagList:
-                        self.__transportToTagMap[targetAddr].update(
+                        self._transportToTagMap[targetAddr].update(
                             [SnmpTagValue(x)
-                             for x in targetAddrTagList.asOctets().split()]
-                        )
+                             for x in targetAddrTagList.asOctets().split()])
 
                     else:
-                        self.__transportToTagMap[targetAddr].add(self.__emptyTag)
+                        self._transportToTagMap[targetAddr].add(self._emptyTag)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
                         '_com2sec: table entries %r/%r hashing failed' % (
-                            targetAddr, targetAddrTagList)
-                    )
+                            targetAddr, targetAddrTagList))
                     continue
 
-            self.__transportBranchId = snmpTargetAddrTAddress.branchVersionId
+            self._transportBranchId = snmpTargetAddrTAddress.branchVersionId
 
-            debug.logger & debug.FLAG_SM and debug.logger('_com2sec: built transport-to-tag map version %s: %s' % (
-                self.__transportBranchId, self.__transportToTagMap))
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '_com2sec: built transport-to-tag map version %s: '
+                '%s' % (self._transportBranchId, self._transportToTagMap))
 
-        snmpTargetParamsSecurityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        snmpTargetParamsSecurityName, = mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityName')
 
-        if self.__paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
-            snmpTargetParamsSecurityModel, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+        if self._paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
+            snmpTargetParamsSecurityModel, = mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityModel')
 
-            self.__nameToModelMap = {}
+            self._nameToModelMap = {}
 
             nextMibNode = snmpTargetParamsSecurityName
 
@@ -213,43 +231,44 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpTargetParamsSecurityName.name):]
 
-                mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
+                mibNode = snmpTargetParamsSecurityModel.getNode(
+                    snmpTargetParamsSecurityModel.name + instId)
 
                 try:
-                    if nextMibNode.syntax not in self.__nameToModelMap:
-                        self.__nameToModelMap[nextMibNode.syntax] = set()
+                    if nextMibNode.syntax not in self._nameToModelMap:
+                        self._nameToModelMap[nextMibNode.syntax] = set()
 
-                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                    self._nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_com2sec: table entries %r/%r hashing failed' % (
-                            nextMibNode.syntax, mibNode.syntax)
-                    )
+                        '_com2sec: table entries %r/%r hashing '
+                        'failed' % (nextMibNode.syntax, mibNode.syntax))
                     continue
 
-            self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
+            self._paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
             # invalidate next map as it include this one
-            self.__communityBranchId = -1
+            self._communityBranchId = -1
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built securityName to securityModel map, version %s: %s' % (
-                    self.__paramsBranchId, self.__nameToModelMap))
+                '_com2sec: built securityName to securityModel map, version '
+                '%s: %s' % (self._paramsBranchId, self._nameToModelMap))
+
+        snmpCommunityName, = mibBuilder.importSymbols(
+            'SNMP-COMMUNITY-MIB', 'snmpCommunityName')
 
-        snmpCommunityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('SNMP-COMMUNITY-MIB',
-                                                                                                   'snmpCommunityName')
-        if self.__communityBranchId != snmpCommunityName.branchVersionId:
+        if self._communityBranchId != snmpCommunityName.branchVersionId:
             (snmpCommunitySecurityName, snmpCommunityContextEngineId,
              snmpCommunityContextName,
-             snmpCommunityTransportTag) = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+             snmpCommunityTransportTag) = mibBuilder.importSymbols(
                 'SNMP-COMMUNITY-MIB', 'snmpCommunitySecurityName',
                 'snmpCommunityContextEngineID', 'snmpCommunityContextName',
                 'snmpCommunityTransportTag'
             )
 
-            self.__communityToTagMap = {}
-            self.__tagAndCommunityToSecurityMap = {}
+            self._communityToTagMap = {}
+            self._tagAndCommunityToSecurityMap = {}
 
             nextMibNode = snmpCommunityName
 
@@ -262,100 +281,125 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 instId = nextMibNode.name[len(snmpCommunityName.name):]
 
-                securityName = snmpCommunitySecurityName.getNode(snmpCommunitySecurityName.name + instId).syntax
+                securityName = snmpCommunitySecurityName.getNode(
+                    snmpCommunitySecurityName.name + instId).syntax
 
                 contextEngineId = snmpCommunityContextEngineId.getNode(
                     snmpCommunityContextEngineId.name + instId).syntax
 
-                contextName = snmpCommunityContextName.getNode(snmpCommunityContextName.name + instId).syntax
+                contextName = snmpCommunityContextName.getNode(
+                    snmpCommunityContextName.name + instId).syntax
 
-                transportTag = snmpCommunityTransportTag.getNode(snmpCommunityTransportTag.name + instId).syntax
+                transportTag = snmpCommunityTransportTag.getNode(
+                    snmpCommunityTransportTag.name + instId).syntax
 
                 _tagAndCommunity = transportTag, nextMibNode.syntax
 
                 try:
-                    if _tagAndCommunity not in self.__tagAndCommunityToSecurityMap:
-                        self.__tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
+                    if _tagAndCommunity not in self._tagAndCommunityToSecurityMap:
+                        self._tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
 
-                    self.__tagAndCommunityToSecurityMap[_tagAndCommunity].add(
-                        (securityName, contextEngineId, contextName)
-                    )
+                    self._tagAndCommunityToSecurityMap[_tagAndCommunity].add(
+                        (securityName, contextEngineId, contextName))
 
-                    if nextMibNode.syntax not in self.__communityToTagMap:
-                        self.__communityToTagMap[nextMibNode.syntax] = set()
+                    if nextMibNode.syntax not in self._communityToTagMap:
+                        self._communityToTagMap[nextMibNode.syntax] = set()
 
-                    self.__communityToTagMap[nextMibNode.syntax].add(transportTag)
+                    self._communityToTagMap[nextMibNode.syntax].add(transportTag)
 
                 except PyAsn1Error:
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_com2sec: table entries %r/%r hashing failed' % (
-                            _tagAndCommunity, nextMibNode.syntax)
-                    )
+                        '_com2sec: table entries %r/%r hashing '
+                        'failed' % (_tagAndCommunity, nextMibNode.syntax))
                     continue
 
-            self.__communityBranchId = snmpCommunityName.branchVersionId
+            self._communityBranchId = snmpCommunityName.branchVersionId
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built communityName to tag map (securityModel %s), version %s: %s' % (
-                    self.SECURITY_MODEL_ID, self.__communityBranchId, self.__communityToTagMap))
+                '_com2sec: built communityName to tag map '
+                '(securityModel %s), version %s: '
+                '%s' % (self.SECURITY_MODEL_ID, self._communityBranchId,
+                        self._communityToTagMap))
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_com2sec: built tag & community to securityName map (securityModel %s), version %s: %s' % (
-                    self.SECURITY_MODEL_ID, self.__communityBranchId, self.__tagAndCommunityToSecurityMap))
-
-        if communityName in self.__communityToTagMap:
-            if transportInformation in self.__transportToTagMap:
-                tags = self.__transportToTagMap[transportInformation].intersection(
-                    self.__communityToTagMap[communityName])
-            elif self.__emptyTag in self.__communityToTagMap[communityName]:
-                tags = [self.__emptyTag]
+                '_com2sec: built tag & community to securityName map '
+                '(securityModel %s), version %s: '
+                '%s' % (self.SECURITY_MODEL_ID, self._communityBranchId,
+                        self._tagAndCommunityToSecurityMap))
+
+        if communityName in self._communityToTagMap:
+            if transportInformation in self._transportToTagMap:
+                tags = self._transportToTagMap[transportInformation].intersection(
+                    self._communityToTagMap[communityName])
+
+            elif self._emptyTag in self._communityToTagMap[communityName]:
+                tags = [self._emptyTag]
+
             else:
-                raise error.StatusInformation(errorIndication=errind.unknownCommunityName)
+                raise error.StatusInformation(
+                    errorIndication=errind.unknownCommunityName)
 
             candidateSecurityNames = []
 
-            for x in [self.__tagAndCommunityToSecurityMap[(t, communityName)] for t in tags]:
+            securityNamesSets = [
+                self._tagAndCommunityToSecurityMap[(t, communityName)]
+                for t in tags
+            ]
+
+            for x in securityNamesSets:
                 candidateSecurityNames.extend(list(x))
 
-            # 5.2.1 (row selection in snmpCommunityTable)
-            # Picks first match but favors entries already in targets table
             if candidateSecurityNames:
-                candidateSecurityNames.sort(
-                    key=lambda x, m=self.__nameToModelMap, v=self.SECURITY_MODEL_ID: (
-                        not int(x[0] in m and v in m[x[0]]), str(x[0]))
-                )
+                candidateSecurityNames.sort(key=self._orderSecurityNames)
+
                 chosenSecurityName = candidateSecurityNames[0]  # min()
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '_com2sec: securityName candidates for communityName \'%s\' are %s; choosing securityName \'%s\'' % (
-                        communityName, candidateSecurityNames, chosenSecurityName[0]))
+                    '_com2sec: securityName candidates for communityName %s '
+                    'are %s; choosing securityName '
+                    '%s' % (communityName, candidateSecurityNames,
+                            chosenSecurityName[0]))
+
                 return chosenSecurityName
 
-        raise error.StatusInformation(errorIndication=errind.unknownCommunityName)
+        raise error.StatusInformation(
+            errorIndication=errind.unknownCommunityName)
+
+    # 5.2.1 (row selection in snmpCommunityTable)
+    # Picks first match but favors entries already in targets table
+    def _orderSecurityNames(self, securityName):
+        return (not int(securityName[0] in self._nameToModelMap and
+                        self.SECURITY_MODEL_ID in self._nameToModelMap[securityName[0]]),
+                str(securityName[0]))
 
     def generateRequestMsg(self, snmpEngine, messageProcessingModel,
                            globalData, maxMessageSize, securityModel,
                            securityEngineId, securityName, securityLevel,
                            scopedPDU):
         msg, = globalData
+
         contextEngineId, contextName, pdu = scopedPDU
 
         # rfc2576: 5.2.3
-        communityName = self._sec2com(snmpEngine, securityName,
-                                      contextEngineId, contextName)
+        communityName = self._sec2com(
+            snmpEngine, securityName, contextEngineId, contextName)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'generateRequestMsg: using community %r for securityModel %r, securityName %r, contextEngineId %r contextName %r' % (
-                communityName, securityModel, securityName, contextEngineId, contextName))
+            'generateRequestMsg: using community %r for securityModel %r, '
+            'securityName %r, contextEngineId %r contextName '
+            '%r' % (communityName, securityModel, securityName,
+                    contextEngineId, contextName))
 
         securityParameters = communityName
 
         msg.setComponentByPosition(1, securityParameters)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('generateRequestMsg: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'generateRequestMsg: %s' % (msg.prettyPrint(),))
 
         try:
             return securityParameters, encoder.encode(msg)
@@ -363,7 +407,9 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         except PyAsn1Error as exc:
             debug.logger & debug.FLAG_MP and debug.logger(
                 'generateRequestMsg: serialization failure: %s' % exc)
-            raise error.StatusInformation(errorIndication=errind.serializationError)
+
+            raise error.StatusInformation(
+                errorIndication=errind.serializationError)
 
     def generateResponseMsg(self, snmpEngine, messageProcessingModel,
                             globalData, maxMessageSize, securityModel,
@@ -371,21 +417,26 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                             scopedPDU, securityStateReference):
         # rfc2576: 5.2.2
         msg, = globalData
+
         contextEngineId, contextName, pdu = scopedPDU
+
         cachedSecurityData = self._cache.pop(securityStateReference)
+
         communityName = cachedSecurityData['communityName']
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'generateResponseMsg: recovered community %r by securityStateReference %s' % (
-                communityName, securityStateReference))
+            'generateResponseMsg: recovered community %r by '
+            'securityStateReference '
+            '%s' % (communityName, securityStateReference))
 
         msg.setComponentByPosition(1, communityName)
         msg.setComponentByPosition(2)
         msg.getComponentByPosition(2).setComponentByType(
-            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            pdu.tagSet, pdu, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
-        debug.logger & debug.FLAG_MP and debug.logger('generateResponseMsg: %s' % (msg.prettyPrint(),))
+        debug.logger & debug.FLAG_MP and debug.logger(
+            'generateResponseMsg: %s' % (msg.prettyPrint(),))
 
         try:
             return communityName, encoder.encode(msg)
@@ -393,11 +444,14 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         except PyAsn1Error as exc:
             debug.logger & debug.FLAG_MP and debug.logger(
                 'generateResponseMsg: serialization failure: %s' % exc)
+
             raise error.StatusInformation(errorIndication=errind.serializationError)
 
     def processIncomingMsg(self, snmpEngine, messageProcessingModel,
                            maxMessageSize, securityParameters, securityModel,
                            securityLevel, wholeMsg, msg):
+        mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
+
         # rfc2576: 5.2.1
         communityName, transportInformation = securityParameters
 
@@ -407,6 +461,7 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
         snmpEngine.observer.storeExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg:writable', scope
         )
+
         snmpEngine.observer.clearExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg:writable'
         )
@@ -418,16 +473,17 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
             )
 
         except error.StatusInformation:
-            snmpInBadCommunityNames, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
+            snmpInBadCommunityNames, = mibBuilder.importSymbols(
                 '__SNMPv2-MIB', 'snmpInBadCommunityNames')
             snmpInBadCommunityNames.syntax += 1
+
             raise error.StatusInformation(
                 errorIndication=errind.unknownCommunityName,
                 communityName=communityName
             )
 
-        snmpEngineID, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB',
-                                                                                              'snmpEngineID')
+        snmpEngineID, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
         securityEngineID = snmpEngineID.syntax
 
@@ -440,24 +496,31 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                  contextEngineId=contextEngineId,
                  contextName=contextName)
         )
+
         snmpEngine.observer.clearExecutionContext(
             snmpEngine, 'rfc2576.processIncomingMsg'
         )
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: looked up securityName %r securityModel %r contextEngineId %r contextName %r by communityName %r AND transportInformation %r' % (
-                securityName, self.SECURITY_MODEL_ID, contextEngineId, contextName, communityName, transportInformation))
+            'processIncomingMsg: looked up securityName %r securityModel %r '
+            'contextEngineId %r contextName %r by communityName %r '
+            'AND transportInformation '
+            '%r' % (securityName, self.SECURITY_MODEL_ID, contextEngineId,
+                    contextName, communityName, transportInformation))
 
         stateReference = self._cache.push(communityName=communityName)
 
         scopedPDU = (contextEngineId, contextName,
                      msg.getComponentByPosition(2).getComponent())
+
         maxSizeResponseScopedPDU = maxMessageSize - 128
+
         securityStateReference = stateReference
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: generated maxSizeResponseScopedPDU %s securityStateReference %s' % (
-                maxSizeResponseScopedPDU, securityStateReference))
+            'processIncomingMsg: generated maxSizeResponseScopedPDU '
+            '%s securityStateReference '
+            '%s' % (maxSizeResponseScopedPDU, securityStateReference))
 
         return (securityEngineID, securityName, scopedPDU,
                 maxSizeResponseScopedPDU, securityStateReference)
diff --git a/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py b/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
index df3db63f..c3578682 100644
--- a/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
+++ b/pysnmp/proto/secmod/rfc3414/auth/hmacmd5.py
@@ -41,11 +41,13 @@ class HmacMd5(base.AbstractAuthenticationService):
         # should be in the substrate. Also, it pre-sets digest placeholder
         # so we hash wholeMsg out of the box.
         # Yes, that's ugly but that's rfc...
-        l = wholeMsg.find(TWELVE_ZEROS)
-        if l == -1:
+        ln = wholeMsg.find(TWELVE_ZEROS)
+
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest placeholder')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
 
         # 6.3.1.1
 
@@ -56,15 +58,13 @@ class HmacMd5(base.AbstractAuthenticationService):
 
         # 6.3.1.2c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 6.3.1.2d --> no-op
 
         # 6.3.1.2e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 6.3.1.3
         # noinspection PyDeprecation,PyCallingNonCallable
@@ -83,15 +83,16 @@ class HmacMd5(base.AbstractAuthenticationService):
         # 6.3.2.1 & 2
         if len(authParameters) != 12:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 6.3.2.3
-        l = wholeMsg.find(authParameters.asOctets())
-        if l == -1:
+        ln = wholeMsg.find(authParameters.asOctets())
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest in wholeMsg')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
+
         authenticatedWholeMsg = wholeHead + TWELVE_ZEROS + wholeTail
 
         # 6.3.2.4a
@@ -101,15 +102,13 @@ class HmacMd5(base.AbstractAuthenticationService):
 
         # 6.3.2.4c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 6.3.2.4d --> no-op
 
         # 6.3.2.4e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 6.3.2.5a
         # noinspection PyDeprecation,PyCallingNonCallable
@@ -125,7 +124,6 @@ class HmacMd5(base.AbstractAuthenticationService):
         # 6.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg
diff --git a/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py b/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
index 4d5498d1..76c35af0 100644
--- a/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
+++ b/pysnmp/proto/secmod/rfc3414/auth/hmacsha.py
@@ -42,11 +42,12 @@ class HmacSha(base.AbstractAuthenticationService):
         # should be in the substrate. Also, it pre-sets digest placeholder
         # so we hash wholeMsg out of the box.
         # Yes, that's ugly but that's rfc...
-        l = wholeMsg.find(TWELVE_ZEROS)
-        if l == -1:
+        ln = wholeMsg.find(TWELVE_ZEROS)
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest placeholder')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
 
         # 7.3.1.2a
         extendedAuthKey = authKey.asNumbers() + FORTY_FOUR_ZEROS
@@ -55,15 +56,13 @@ class HmacSha(base.AbstractAuthenticationService):
 
         # 7.3.1.2c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 7.3.1.2d -- no-op
 
         # 7.3.1.2e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 7.3.1.3
         d1 = sha1(k1.asOctets() + wholeMsg).digest()
@@ -80,15 +79,16 @@ class HmacSha(base.AbstractAuthenticationService):
         # 7.3.2.1 & 2
         if len(authParameters) != 12:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 7.3.2.3
-        l = wholeMsg.find(authParameters.asOctets())
-        if l == -1:
+        ln = wholeMsg.find(authParameters.asOctets())
+        if ln == -1:
             raise error.ProtocolError('Cant locate digest in wholeMsg')
-        wholeHead = wholeMsg[:l]
-        wholeTail = wholeMsg[l + 12:]
+
+        wholeHead = wholeMsg[:ln]
+        wholeTail = wholeMsg[ln + 12:]
+
         authenticatedWholeMsg = wholeHead + TWELVE_ZEROS + wholeTail
 
         # 7.3.2.4a
@@ -98,15 +98,13 @@ class HmacSha(base.AbstractAuthenticationService):
 
         # 7.3.2.4c
         k1 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.IPAD))
 
         # 7.3.2.4d --> no-op
 
         # 7.3.2.4e
         k2 = univ.OctetString(
-            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD)
-        )
+            map(lambda x, y: x ^ y, extendedAuthKey, self.OPAD))
 
         # 7.3.2.5a
         d1 = sha1(k1.asOctets() + authenticatedWholeMsg).digest()
@@ -120,7 +118,6 @@ class HmacSha(base.AbstractAuthenticationService):
         # 7.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg
diff --git a/pysnmp/proto/secmod/rfc3414/localkey.py b/pysnmp/proto/secmod/rfc3414/localkey.py
index 144342fa..bc4faa91 100644
--- a/pysnmp/proto/secmod/rfc3414/localkey.py
+++ b/pysnmp/proto/secmod/rfc3414/localkey.py
@@ -12,9 +12,12 @@ from pyasn1.type import univ
 
 def hashPassphrase(passphrase, hashFunc):
     passphrase = univ.OctetString(passphrase).asOctets()
+
     hasher = hashFunc()
+
     ringBuffer = passphrase * (64 // len(passphrase) + 1)
     ringBufferLen = len(ringBuffer)
+
     count = 0
     mark = 0
 
@@ -25,9 +28,11 @@ def hashPassphrase(passphrase, hashFunc):
             mark = e
 
         else:
-            hasher.update(
-                ringBuffer[mark:ringBufferLen] + ringBuffer[0:e - ringBufferLen]
-            )
+            chunk = ringBuffer[mark:ringBufferLen]
+            chunk += ringBuffer[0:e - ringBufferLen]
+
+            hasher.update(chunk)
+
             mark = e - ringBufferLen
 
         count += 1
@@ -36,11 +41,13 @@ def hashPassphrase(passphrase, hashFunc):
 
 
 def passwordToKey(passphrase, snmpEngineId, hashFunc):
-    return localizeKey(hashPassphrase(passphrase, hashFunc), snmpEngineId, hashFunc)
+    return localizeKey(
+        hashPassphrase(passphrase, hashFunc), snmpEngineId, hashFunc)
 
 
 def localizeKey(passKey, snmpEngineId, hashFunc):
     passKey = univ.OctetString(passKey).asOctets()
+
     # noinspection PyDeprecation,PyCallingNonCallable
     return hashFunc(passKey + snmpEngineId.asOctets() + passKey).digest()
 
diff --git a/pysnmp/proto/secmod/rfc3414/priv/des.py b/pysnmp/proto/secmod/rfc3414/priv/des.py
index 5128a662..10058aeb 100644
--- a/pysnmp/proto/secmod/rfc3414/priv/des.py
+++ b/pysnmp/proto/secmod/rfc3414/priv/des.py
@@ -38,32 +38,39 @@ class Des(base.AbstractEncryptionService):
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+
         return localPrivKey[:self.KEY_SIZE]
 
     # 8.1.1.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots):
+    def _getEncryptionKey(self, privKey, snmpEngineBoots):
         desKey = privKey[:8]
         preIV = privKey[8:16]
 
@@ -77,42 +84,47 @@ class Des(base.AbstractEncryptionService):
                 self.local_int >> 16 & 0xff,
                 self.local_int >> 8 & 0xff,
                 self.local_int & 0xff]
+
         if self.local_int == 0xffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
+        iv = map(lambda x, y: x ^ y, salt, preIV.asNumbers())
+
         return (desKey.asOctets(),
                 univ.OctetString(salt).asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt, preIV.asNumbers())).asOctets())
+                univ.OctetString(iv).asOctets())
 
     @staticmethod
-    def __getDecryptionKey(privKey, salt):
-        return (privKey[:8].asOctets(),
-                univ.OctetString(map(lambda x, y: x ^ y, salt.asNumbers(), privKey[8:16].asNumbers())).asOctets())
+    def _getDecryptionKey(privKey, salt):
+        iv = map(lambda x, y: x ^ y, salt.asNumbers(),
+                 privKey[8:16].asNumbers())
+
+        return privKey[:8].asOctets(), univ.OctetString(iv).asOctets()
 
     # 8.2.4.1
     def encryptData(self, encryptKey, privParameters, dataToEncrypt):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
         # 8.3.1.1
-        desKey, salt, iv = self.__getEncryptionKey(
-            encryptKey, snmpEngineBoots
-        )
+        desKey, salt, iv = self._getEncryptionKey(encryptKey, snmpEngineBoots)
 
         # 8.3.1.2
         privParameters = univ.OctetString(salt)
 
         # 8.1.1.2
-        plaintext = dataToEncrypt + univ.OctetString((0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
+        plaintext = dataToEncrypt
+        plaintext += univ.OctetString(
+            (0,) * (8 - len(dataToEncrypt) % 8)).asOctets()
 
         try:
             ciphertext = des.encrypt(plaintext, desKey, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         # 8.3.1.3 & 4
         return univ.OctetString(ciphertext), privParameters
@@ -124,19 +136,17 @@ class Des(base.AbstractEncryptionService):
         # 8.3.2.1
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         # 8.3.2.2 no-op
 
         # 8.3.2.3
-        desKey, iv = self.__getDecryptionKey(decryptKey, salt)
+        desKey, iv = self._getDecryptionKey(decryptKey, salt)
 
         # 8.3.2.4 -> 8.1.1.3
         if len(encryptedData) % 8 != 0:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         try:
             # 8.3.2.6
@@ -144,5 +154,4 @@ class Des(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
diff --git a/pysnmp/proto/secmod/rfc3414/service.py b/pysnmp/proto/secmod/rfc3414/service.py
index f9bf056b..0a8f54e5 100644
--- a/pysnmp/proto/secmod/rfc3414/service.py
+++ b/pysnmp/proto/secmod/rfc3414/service.py
@@ -38,15 +38,26 @@ from pysnmp.smi.error import NoSuchInstanceError
 
 class UsmSecurityParameters(rfc1155.TypeCoercionHackMixIn, univ.Sequence):
     componentType = namedtype.NamedTypes(
-        namedtype.NamedType('msgAuthoritativeEngineId', univ.OctetString()),
-        namedtype.NamedType('msgAuthoritativeEngineBoots',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgAuthoritativeEngineTime',
-                            univ.Integer().subtype(subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
-        namedtype.NamedType('msgUserName',
-                            univ.OctetString().subtype(subtypeSpec=constraint.ValueSizeConstraint(0, 32))),
-        namedtype.NamedType('msgAuthenticationParameters', univ.OctetString()),
-        namedtype.NamedType('msgPrivacyParameters', univ.OctetString())
+        namedtype.NamedType(
+            'msgAuthoritativeEngineId', univ.OctetString()),
+        namedtype.NamedType(
+            'msgAuthoritativeEngineBoots',
+            univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgAuthoritativeEngineTime',
+            univ.Integer().subtype(
+                subtypeSpec=constraint.ValueRangeConstraint(0, 2147483647))),
+        namedtype.NamedType(
+            'msgUserName',
+            univ.OctetString().subtype(
+                subtypeSpec=constraint.ValueSizeConstraint(0, 32))),
+        namedtype.NamedType(
+            'msgAuthenticationParameters',
+            univ.OctetString()),
+        namedtype.NamedType(
+            'msgPrivacyParameters',
+            univ.OctetString())
     )
 
 
@@ -56,10 +67,14 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
     AUTH_SERVICES = {
         hmacmd5.HmacMd5.SERVICE_ID: hmacmd5.HmacMd5(),
         hmacsha.HmacSha.SERVICE_ID: hmacsha.HmacSha(),
-        hmacsha2.HmacSha2.SHA224_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA224_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA256_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA256_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA384_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA384_SERVICE_ID),
-        hmacsha2.HmacSha2.SHA512_SERVICE_ID: hmacsha2.HmacSha2(hmacsha2.HmacSha2.SHA512_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA224_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA224_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA256_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA256_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA384_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA384_SERVICE_ID),
+        hmacsha2.HmacSha2.SHA512_SERVICE_ID: hmacsha2.HmacSha2(
+            hmacsha2.HmacSha2.SHA512_SERVICE_ID),
         noauth.NoAuth.SERVICE_ID: noauth.NoAuth(),
     }
 
@@ -76,21 +91,23 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
     def __init__(self):
         AbstractSecurityModel.__init__(self)
-        self.__securityParametersSpec = UsmSecurityParameters()
-        self.__timeline = {}
-        self.__timelineExpQueue = {}
-        self.__expirationTimer = 0
-        self.__paramsBranchId = -1
+        self._securityParametersSpec = UsmSecurityParameters()
+        self._timeline = {}
+        self._timelineExpQueue = {}
+        self._expirationTimer = 0
+        self._paramsBranchId = -1
 
-    def __sec2usr(self, snmpEngine, securityName, securityEngineID=None):
+    def _sec2usr(self, snmpEngine, securityName, securityEngineID=None):
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
-        usmUserEngineID, = mibBuilder.importSymbols('SNMP-USER-BASED-SM-MIB',
-                                                    'usmUserEngineID')
-        if self.__paramsBranchId != usmUserEngineID.branchVersionId:
+
+        usmUserEngineID, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEngineID')
+
+        if self._paramsBranchId != usmUserEngineID.branchVersionId:
             usmUserName, usmUserSecurityName = mibBuilder.importSymbols(
                 'SNMP-USER-BASED-SM-MIB', 'usmUserName', 'usmUserSecurityName')
 
-            self.__securityToUserMap = {}
+            self._securityToUserMap = {}
 
             nextMibNode = usmUserEngineID
 
@@ -99,108 +116,138 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     nextMibNode = usmUserEngineID.getNextNode(nextMibNode.name)
 
                 except NoSuchInstanceError:
-                    self.__paramsBranchId = usmUserEngineID.branchVersionId
+                    self._paramsBranchId = usmUserEngineID.branchVersionId
+
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        '_sec2usr: built snmpEngineId + securityName to userName map, version %s: %r' % (
-                            self.__paramsBranchId, self.__securityToUserMap))
+                        '_sec2usr: built snmpEngineId + securityName to '
+                        'userName map, version %s: %r' % (
+                            self._paramsBranchId, self._securityToUserMap))
                     break
 
                 instId = nextMibNode.name[len(usmUserSecurityName.name):]
 
-                __engineID = usmUserEngineID.getNode(usmUserEngineID.name + instId).syntax
-                __userName = usmUserName.getNode(usmUserName.name + instId).syntax
-                __securityName = usmUserSecurityName.getNode(usmUserSecurityName.name + instId).syntax
+                _engineID = usmUserEngineID.getNode(
+                    usmUserEngineID.name + instId).syntax
+                _userName = usmUserName.getNode(
+                    usmUserName.name + instId).syntax
+                _securityName = usmUserSecurityName.getNode(
+                    usmUserSecurityName.name + instId).syntax
 
-                k = __engineID, __securityName
+                k = _engineID, _securityName
 
                 # first (lesser) securityName wins
-                if k not in self.__securityToUserMap:
-                    self.__securityToUserMap[k] = __userName
+                if k not in self._securityToUserMap:
+                    self._securityToUserMap[k] = _userName
 
         if securityEngineID is None:
-            snmpEngineID, = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
+            snmpEngineID, = mibBuilder.importSymbols(
+                '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
             securityEngineID = snmpEngineID.syntax
 
         try:
-            userName = self.__securityToUserMap[(securityEngineID, securityName)]
+            userName = self._securityToUserMap[(securityEngineID, securityName)]
+
         except KeyError:
             debug.logger & debug.FLAG_SM and debug.logger(
-                '_sec2usr: no entry exists for snmpEngineId %r, securityName %r' % (securityEngineID, securityName))
+                '_sec2usr: no entry exists for snmpEngineId %r, securityName '
+                '%r' % (securityEngineID, securityName))
             raise NoSuchInstanceError()  # emulate MIB lookup
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            '_sec2usr: using userName %r for snmpEngineId %r, securityName %r' % (
-                userName, securityEngineID, securityName))
+            '_sec2usr: using userName %r for snmpEngineId %r, securityName '
+            '%r' % (userName, securityEngineID, securityName))
 
         return userName
 
     @staticmethod
-    def __getUserInfo(mibInstrumController, securityEngineID, userName):
-        usmUserEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry'
-        )
+    def _getUserInfo(mibInstrumController, securityEngineID, userName):
+        mibBuilder = mibInstrumController.mibBuilder
+
+        usmUserEntry, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+
         tblIdx = usmUserEntry.getInstIdFromIndices(securityEngineID, userName)
+
         # Get userName & securityName
         usmUserName = usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx).syntax
         usmUserSecurityName = usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx).syntax
+
         # Get protocols
         usmUserAuthProtocol = usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx).syntax
         usmUserPrivProtocol = usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx).syntax
+
         # Get keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
-        pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (1,) + tblIdx).syntax
-        pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (2,) + tblIdx).syntax
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
+
+        pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (1,) + tblIdx).syntax
+        pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (2,) + tblIdx).syntax
+
         return (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
                 pysnmpUsmKeyAuthLocalized, usmUserPrivProtocol,
                 pysnmpUsmKeyPrivLocalized)
 
-    def __cloneUserInfo(self, snmpEngine, securityEngineID, userName):
+    def _cloneUserInfo(self, snmpEngine, securityEngineID, userName):
         mibInstrumController = snmpEngine.msgAndPduDsp.mibInstrumController
+        mibBuilder = mibInstrumController.mibBuilder
+
+        snmpEngineID, = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')
 
-        snmpEngineID, = mibInstrumController.mibBuilder.importSymbols(
-            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID'
-        )
         # Proto entry
-        usmUserEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry'
-        )
+        usmUserEntry, = mibBuilder.importSymbols(
+            'SNMP-USER-BASED-SM-MIB', 'usmUserEntry')
+
         tblIdx1 = usmUserEntry.getInstIdFromIndices(
-            snmpEngineID.syntax, userName
-        )
+            snmpEngineID.syntax, userName)
+
         # Get proto protocols
-        usmUserName = usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx1)
-        usmUserSecurityName = usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx1)
-        usmUserCloneFrom = usmUserEntry.getNode(usmUserEntry.name + (4,) + tblIdx1)
-        usmUserAuthProtocol = usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx1)
-        usmUserPrivProtocol = usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx1)
+        usmUserName = usmUserEntry.getNode(
+            usmUserEntry.name + (2,) + tblIdx1)
+        usmUserSecurityName = usmUserEntry.getNode(
+            usmUserEntry.name + (3,) + tblIdx1)
+        usmUserCloneFrom = usmUserEntry.getNode(
+            usmUserEntry.name + (4,) + tblIdx1)
+        usmUserAuthProtocol = usmUserEntry.getNode(
+            usmUserEntry.name + (5,) + tblIdx1)
+        usmUserPrivProtocol = usmUserEntry.getNode(
+            usmUserEntry.name + (8,) + tblIdx1)
+
         # Get proto keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
-        pysnmpUsmKeyAuth = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (3,) + tblIdx1)
-        pysnmpUsmKeyPriv = pysnmpUsmKeyEntry.getNode(pysnmpUsmKeyEntry.name + (4,) + tblIdx1)
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
+
+        pysnmpUsmKeyAuth = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (3,) + tblIdx1)
+        pysnmpUsmKeyPriv = pysnmpUsmKeyEntry.getNode(
+            pysnmpUsmKeyEntry.name + (4,) + tblIdx1)
 
         # Create new row from proto values
 
-        tblIdx2 = usmUserEntry.getInstIdFromIndices(securityEngineID, userName)
+        tblIdx2 = usmUserEntry.getInstIdFromIndices(
+            securityEngineID, userName)
 
         # New inactive row
         mibInstrumController.writeMibObjects(
-            (usmUserEntry.name + (13,) + tblIdx2, 5), snmpEngine=snmpEngine
-        )
+            (usmUserEntry.name + (13,) + tblIdx2, 5), snmpEngine=snmpEngine)
 
         # Set user&securityNames
-        usmUserEntry.getNode(usmUserEntry.name + (2,) + tblIdx2).syntax = usmUserName.syntax
-        usmUserEntry.getNode(usmUserEntry.name + (3,) + tblIdx2).syntax = usmUserSecurityName.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (2,) + tblIdx2).syntax = usmUserName.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (3,) + tblIdx2).syntax = usmUserSecurityName.syntax
 
         # Store a reference to original row
-        usmUserEntry.getNode(usmUserEntry.name + (4,) + tblIdx2).syntax = usmUserCloneFrom.syntax.clone(tblIdx1)
+        usmUserEntry.getNode(
+            usmUserEntry.name + (4,) + tblIdx2).syntax = usmUserCloneFrom.syntax.clone(tblIdx1)
 
         # Set protocols
-        usmUserEntry.getNode(usmUserEntry.name + (5,) + tblIdx2).syntax = usmUserAuthProtocol.syntax
-        usmUserEntry.getNode(usmUserEntry.name + (8,) + tblIdx2).syntax = usmUserPrivProtocol.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (5,) + tblIdx2).syntax = usmUserAuthProtocol.syntax
+        usmUserEntry.getNode(
+            usmUserEntry.name + (8,) + tblIdx2).syntax = usmUserPrivProtocol.syntax
 
         # Activate row
         mibInstrumController.writeMibObjects(
@@ -208,98 +255,124 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         )
 
         # Localize and set keys
-        pysnmpUsmKeyEntry, = mibInstrumController.mibBuilder.importSymbols(
-            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry'
-        )
+        pysnmpUsmKeyEntry, = mibBuilder.importSymbols(
+            'PYSNMP-USM-MIB', 'pysnmpUsmKeyEntry')
         pysnmpUsmKeyAuthLocalized = pysnmpUsmKeyEntry.getNode(
-            pysnmpUsmKeyEntry.name + (1,) + tblIdx2
-        )
+            pysnmpUsmKeyEntry.name + (1,) + tblIdx2)
+
         if usmUserAuthProtocol.syntax in self.AUTH_SERVICES:
             localizeKey = self.AUTH_SERVICES[usmUserAuthProtocol.syntax].localizeKey
-            localAuthKey = localizeKey(pysnmpUsmKeyAuth.syntax,
-                                       securityEngineID)
+            localAuthKey = localizeKey(
+                pysnmpUsmKeyAuth.syntax, securityEngineID)
+
         else:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedAuthProtocol
-            )
+                errorIndication=errind.unsupportedAuthProtocol)
+
         if localAuthKey is not None:
             pysnmpUsmKeyAuthLocalized.syntax = pysnmpUsmKeyAuthLocalized.syntax.clone(localAuthKey)
+
         pysnmpUsmKeyPrivLocalized = pysnmpUsmKeyEntry.getNode(
-            pysnmpUsmKeyEntry.name + (2,) + tblIdx2
-        )
+            pysnmpUsmKeyEntry.name + (2,) + tblIdx2)
+
         if usmUserPrivProtocol.syntax in self.PRIV_SERVICES:
             localizeKey = self.PRIV_SERVICES[usmUserPrivProtocol.syntax].localizeKey
-            localPrivKey = localizeKey(usmUserAuthProtocol.syntax,
-                                       pysnmpUsmKeyPriv.syntax,
-                                       securityEngineID)
+            localPrivKey = localizeKey(
+                usmUserAuthProtocol.syntax, pysnmpUsmKeyPriv.syntax,
+                securityEngineID)
+
         else:
-            raise error.StatusInformation(errorIndication=errind.unsupportedPrivProtocol)
+            raise error.StatusInformation(
+                errorIndication=errind.unsupportedPrivProtocol)
+
         if localPrivKey is not None:
             pysnmpUsmKeyPrivLocalized.syntax = pysnmpUsmKeyPrivLocalized.syntax.clone(localPrivKey)
+
         return (usmUserName.syntax, usmUserSecurityName.syntax,
                 usmUserAuthProtocol.syntax, pysnmpUsmKeyAuthLocalized.syntax,
                 usmUserPrivProtocol.syntax, pysnmpUsmKeyPrivLocalized.syntax)
 
-    def __generateRequestOrResponseMsg(self, snmpEngine,
-                                       messageProcessingModel,
-                                       globalData, maxMessageSize,
-                                       securityModel, securityEngineID,
-                                       securityName, securityLevel,
-                                       scopedPDU, securityStateReference):
+    def _generateRequestOrResponseMsg(self, snmpEngine,
+                                      messageProcessingModel,
+                                      globalData, maxMessageSize,
+                                      securityModel, securityEngineID,
+                                      securityName, securityLevel,
+                                      scopedPDU, securityStateReference):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
-        snmpEngineID = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+
+        snmpEngineID = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
 
         # 3.1.1
         if securityStateReference is not None:
             # 3.1.1a
             cachedSecurityData = self._cache.pop(securityStateReference)
+
             usmUserName = cachedSecurityData['msgUserName']
+
             if 'usmUserSecurityName' in cachedSecurityData:
                 usmUserSecurityName = cachedSecurityData['usmUserSecurityName']
+
             else:
                 usmUserSecurityName = usmUserName
+
             if 'usmUserAuthProtocol' in cachedSecurityData:
                 usmUserAuthProtocol = cachedSecurityData['usmUserAuthProtocol']
+
             else:
                 usmUserAuthProtocol = noauth.NoAuth.SERVICE_ID
+
             if 'usmUserAuthKeyLocalized' in cachedSecurityData:
                 usmUserAuthKeyLocalized = cachedSecurityData['usmUserAuthKeyLocalized']
+
             else:
                 usmUserAuthKeyLocalized = None
+
             if 'usmUserPrivProtocol' in cachedSecurityData:
                 usmUserPrivProtocol = cachedSecurityData['usmUserPrivProtocol']
+
             else:
                 usmUserPrivProtocol = nopriv.NoPriv.SERVICE_ID
+
             if 'usmUserPrivKeyLocalized' in cachedSecurityData:
                 usmUserPrivKeyLocalized = cachedSecurityData['usmUserPrivKeyLocalized']
+
             else:
                 usmUserPrivKeyLocalized = None
+
             securityEngineID = snmpEngineID
-            debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: user info read from cache')
+
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '__generateRequestOrResponseMsg: user info read from cache')
+
         elif securityName:
             # 3.1.1b
             try:
                 (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
                  usmUserAuthKeyLocalized, usmUserPrivProtocol,
-                 usmUserPrivKeyLocalized) = self.__getUserInfo(
+                 usmUserPrivKeyLocalized) = self._getUserInfo(
                     snmpEngine.msgAndPduDsp.mibInstrumController,
                     securityEngineID,
-                    self.__sec2usr(snmpEngine, securityName, securityEngineID)
+                    self._sec2usr(snmpEngine, securityName, securityEngineID)
                 )
-                debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: read user info')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    '__generateRequestOrResponseMsg: read user info')
 
             except NoSuchInstanceError:
-                pysnmpUsmDiscovery, = mibBuilder.importSymbols('__PYSNMP-USM-MIB', 'pysnmpUsmDiscovery')
+                pysnmpUsmDiscovery, = mibBuilder.importSymbols(
+                    '__PYSNMP-USM-MIB', 'pysnmpUsmDiscovery')
+
                 reportUnknownName = not pysnmpUsmDiscovery.syntax
+
                 if not reportUnknownName:
                     try:
                         (usmUserName, usmUserSecurityName,
                          usmUserAuthProtocol, usmUserAuthKeyLocalized,
                          usmUserPrivProtocol,
-                         usmUserPrivKeyLocalized) = self.__cloneUserInfo(
-                            snmpEngine,
-                            securityEngineID,
-                            self.__sec2usr(snmpEngine, securityName)
+                         usmUserPrivKeyLocalized) = self._cloneUserInfo(
+                            snmpEngine, securityEngineID,
+                            self._sec2usr(snmpEngine, securityName)
                         )
 
                     except NoSuchInstanceError:
@@ -307,31 +380,40 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
                 if reportUnknownName:
                     raise error.StatusInformation(
-                        errorIndication=errind.unknownSecurityName
-                    )
+                        errorIndication=errind.unknownSecurityName)
 
-                debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: clone user info')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    '__generateRequestOrResponseMsg: clone user info')
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
                     '__generateRequestOrResponseMsg: %s' % exc)
-                snmpInGenErrs, = mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInGenErrs')
+
+                snmpInGenErrs, = mibBuilder.importSymbols(
+                    '__SNMPv2-MIB', 'snmpInGenErrs')
                 snmpInGenErrs.syntax += 1
-                raise error.StatusInformation(
-                    errorIndication=errind.invalidMsg
-                )
+
+                raise error.StatusInformation(errorIndication=errind.invalidMsg)
+
         else:
             # empty username used for engineID discovery
             usmUserName = usmUserSecurityName = null
             usmUserAuthProtocol = noauth.NoAuth.SERVICE_ID
             usmUserPrivProtocol = nopriv.NoPriv.SERVICE_ID
+
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
-            debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: use empty USM data')
+
+            debug.logger & debug.FLAG_SM and debug.logger(
+                '__generateRequestOrResponseMsg: use empty USM data')
 
         # noinspection PyUnboundLocalVariable
         debug.logger & debug.FLAG_SM and debug.logger(
-            '__generateRequestOrResponseMsg: local usmUserName %r usmUserSecurityName %r usmUserAuthProtocol %s usmUserPrivProtocol %s securityEngineID %r securityName %r' % (
-                usmUserName, usmUserSecurityName, usmUserAuthProtocol, usmUserPrivProtocol, securityEngineID, securityName))
+            '__generateRequestOrResponseMsg: local usmUserName %r '
+            'usmUserSecurityName %r usmUserAuthProtocol %s '
+            'usmUserPrivProtocol %s securityEngineID %r '
+            'securityName %r' % (
+                usmUserName, usmUserSecurityName, usmUserAuthProtocol,
+                usmUserPrivProtocol, securityEngineID, securityName))
 
         msg = globalData
 
@@ -340,22 +422,21 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             if (usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID or
                     usmUserPrivProtocol == nopriv.NoPriv.SERVICE_ID):
                 raise error.StatusInformation(
-                    errorIndication=errind.unsupportedSecurityLevel
-                )
+                    errorIndication=errind.unsupportedSecurityLevel)
 
         # 3.1.3
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                 raise error.StatusInformation(
-                    errorIndication=errind.unsupportedSecurityLevel
-                )
+                    errorIndication=errind.unsupportedSecurityLevel)
 
-        securityParameters = self.__securityParametersSpec
+        securityParameters = self._securityParametersSpec
 
         scopedPDUData = msg.setComponentByPosition(3).getComponentByPosition(3)
+
         scopedPDUData.setComponentByPosition(
-            0, scopedPDU, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, scopedPDU, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         snmpEngineBoots = snmpEngineTime = 0
 
@@ -364,161 +445,180 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
             # 3.1.6.b
             if pdu.tagSet in rfc3411.UNCONFIRMED_CLASS_PDUS:
-                (snmpEngineBoots,
-                 snmpEngineTime) = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots', 'snmpEngineTime')
+                snmpEngineBoots, snmpEngineTime = mibBuilder.importSymbols(
+                    '__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots',
+                    'snmpEngineTime')
 
                 snmpEngineBoots = snmpEngineBoots.syntax
                 snmpEngineTime = snmpEngineTime.syntax.clone()
 
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: read snmpEngineBoots, snmpEngineTime from LCD')
+                    '__generateRequestOrResponseMsg: read snmpEngineBoots, '
+                    'snmpEngineTime from LCD')
 
             # 3.1.6a
-            elif securityEngineID in self.__timeline:
+            elif securityEngineID in self._timeline:
                 (snmpEngineBoots,
                  snmpEngineTime,
                  latestReceivedEngineTime,
-                 latestUpdateTimestamp) = self.__timeline[securityEngineID]
+                 latestUpdateTimestamp) = self._timeline[securityEngineID]
 
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: read snmpEngineBoots, snmpEngineTime from timeline')
+                    '__generateRequestOrResponseMsg: read snmpEngineBoots, '
+                    'snmpEngineTime from timeline')
 
             # 3.1.6.c
             else:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: assuming zero snmpEngineBoots, snmpEngineTime')
+                    '__generateRequestOrResponseMsg: assuming zero '
+                    'snmpEngineBoots, snmpEngineTime')
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: use snmpEngineBoots %s snmpEngineTime %s for securityEngineID %r' % (
+                '__generateRequestOrResponseMsg: use snmpEngineBoots %s '
+                'snmpEngineTime %s for securityEngineID %r' % (
                     snmpEngineBoots, snmpEngineTime, securityEngineID))
 
         # 3.1.4a
         if securityLevel == 3:
             if usmUserPrivProtocol in self.PRIV_SERVICES:
                 privHandler = self.PRIV_SERVICES[usmUserPrivProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.encryptionError
-                )
+                    errorIndication=errind.encryptionError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU %s' % scopedPDU.prettyPrint())
+                '__generateRequestOrResponseMsg: scopedPDU '
+                '%s' % scopedPDU.prettyPrint())
 
             try:
                 dataToEncrypt = encoder.encode(scopedPDU)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: scopedPDU serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: scopedPDU serialization '
+                    'error: %s' % exc)
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU encoded into %s' % debug.hexdump(dataToEncrypt))
+                '__generateRequestOrResponseMsg: scopedPDU encoded into '
+                '%s' % debug.hexdump(dataToEncrypt))
 
             # noinspection PyUnboundLocalVariable
-            (encryptedData,
-             privParameters) = privHandler.encryptData(
+            encryptedData, privParameters = privHandler.encryptData(
                 usmUserPrivKeyLocalized,
-                (snmpEngineBoots, snmpEngineTime, None), dataToEncrypt
-            )
+                (snmpEngineBoots, snmpEngineTime, None),
+                dataToEncrypt)
 
             securityParameters.setComponentByPosition(
-                5, privParameters, verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                5, privParameters, verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
+
             scopedPDUData.setComponentByPosition(
-                1, encryptedData, verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                1, encryptedData, verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: scopedPDU ciphered into %s' % debug.hexdump(encryptedData))
+                '__generateRequestOrResponseMsg: scopedPDU ciphered into '
+                '%s' % debug.hexdump(encryptedData))
 
         # 3.1.4b
         elif securityLevel == 1 or securityLevel == 2:
             securityParameters.setComponentByPosition(5, '')
 
-        debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: %s' % scopedPDUData.prettyPrint())
+        debug.logger & debug.FLAG_SM and debug.logger(
+            '__generateRequestOrResponseMsg: %s' % scopedPDUData.prettyPrint())
 
         # 3.1.5
         securityParameters.setComponentByPosition(
-            0, securityEngineID, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            0, securityEngineID, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         securityParameters.setComponentByPosition(
-            1, snmpEngineBoots, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            1, snmpEngineBoots, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
+
         securityParameters.setComponentByPosition(
-            2, snmpEngineTime, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            2, snmpEngineTime, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 3.1.7
         securityParameters.setComponentByPosition(
-            3, usmUserName, verifyConstraints=False, matchTags=False, matchConstraints=False
-        )
+            3, usmUserName, verifyConstraints=False, matchTags=False,
+            matchConstraints=False)
 
         # 3.1.8a
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol in self.AUTH_SERVICES:
                 authHandler = self.AUTH_SERVICES[usmUserAuthProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.authenticationFailure
-                )
+                    errorIndication=errind.authenticationFailure)
 
             # extra-wild hack to facilitate BER substrate in-place re-write
             securityParameters.setComponentByPosition(
-                4, '\x00' * authHandler.digestLength
-            )
+                4, '\x00' * authHandler.digestLength)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: %s' % (securityParameters.prettyPrint(),))
+                '__generateRequestOrResponseMsg: '
+                '%s' % (securityParameters.prettyPrint(),))
 
             try:
-                msg.setComponentByPosition(2, encoder.encode(securityParameters), verifyConstraints=False)
+                msg.setComponentByPosition(
+                    2, encoder.encode(securityParameters),
+                    verifyConstraints=False)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: securityParameters serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: securityParameters '
+                    'serialization error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: auth outgoing msg: %s' % msg.prettyPrint())
+                '__generateRequestOrResponseMsg: auth outgoing msg: '
+                '%s' % msg.prettyPrint())
 
             try:
                 wholeMsg = encoder.encode(msg)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: msg serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: msg serialization '
+                    'error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             # noinspection PyUnboundLocalVariable
             authenticatedWholeMsg = authHandler.authenticateOutgoingMsg(
-                usmUserAuthKeyLocalized, wholeMsg
-            )
+                usmUserAuthKeyLocalized, wholeMsg)
 
         # 3.1.8b
         else:
             securityParameters.setComponentByPosition(
-                4, '', verifyConstraints=False, matchTags=False, matchConstraints=False
-            )
+                4, '', verifyConstraints=False, matchTags=False,
+                matchConstraints=False)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                '__generateRequestOrResponseMsg: %s' % (securityParameters.prettyPrint(),))
+                '__generateRequestOrResponseMsg: '
+                '%s' % (securityParameters.prettyPrint(),))
 
             try:
-                msg.setComponentByPosition(2, encoder.encode(securityParameters), verifyConstraints=False, matchTags=False, matchConstraints=False)
+                msg.setComponentByPosition(
+                    2, encoder.encode(securityParameters), verifyConstraints=False,
+                    matchTags=False, matchConstraints=False)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: secutiryParameters serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: securityParameters '
+                    'serialization error: %s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
             try:
                 debug.logger & debug.FLAG_SM and debug.logger(
@@ -527,13 +627,16 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    '__generateRequestOrResponseMsg: msg serialization error: %s' % exc)
+                    '__generateRequestOrResponseMsg: msg serialization error: '
+                    '%s' % exc)
+
                 raise error.StatusInformation(
-                    errorIndication=errind.serializationError
-                )
+                    errorIndication=errind.serializationError)
 
-        debug.logger & debug.FLAG_SM and debug.logger('__generateRequestOrResponseMsg: %s outgoing msg: %s' % (
-            securityLevel > 1 and "authenticated" or "plain", debug.hexdump(authenticatedWholeMsg)))
+        debug.logger & debug.FLAG_SM and debug.logger(
+            '__generateRequestOrResponseMsg: %s outgoing msg: '
+            '%s' % (securityLevel > 1 and "authenticated" or
+                    "plain", debug.hexdump(authenticatedWholeMsg)))
 
         # 3.1.9
         return msg.getComponentByPosition(2), authenticatedWholeMsg
@@ -542,88 +645,99 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                            globalData, maxMessageSize, securityModel,
                            securityEngineID, securityName, securityLevel,
                            scopedPDU):
-        return self.__generateRequestOrResponseMsg(snmpEngine,
-                                                   messageProcessingModel,
-                                                   globalData,
-                                                   maxMessageSize,
-                                                   securityModel,
-                                                   securityEngineID,
-                                                   securityName,
-                                                   securityLevel,
-                                                   scopedPDU,
-                                                   None)
+
+        return self._generateRequestOrResponseMsg(
+            snmpEngine, messageProcessingModel, globalData,
+            maxMessageSize, securityModel, securityEngineID,
+            securityName, securityLevel, scopedPDU, None)
 
     def generateResponseMsg(self, snmpEngine, messageProcessingModel,
                             globalData, maxMessageSize, securityModel,
                             securityEngineID, securityName, securityLevel,
                             scopedPDU, securityStateReference):
-        return self.__generateRequestOrResponseMsg(
+
+        return self._generateRequestOrResponseMsg(
             snmpEngine, messageProcessingModel, globalData,
             maxMessageSize, securityModel, securityEngineID,
-            securityName, securityLevel, scopedPDU, securityStateReference
+            securityName, securityLevel, scopedPDU,
+            securityStateReference
         )
 
     # 3.2
     def processIncomingMsg(self, snmpEngine, messageProcessingModel,
                            maxMessageSize, securityParameters,
                            securityModel, securityLevel, wholeMsg, msg):
+
         mibBuilder = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder
 
         # 3.2.9 -- moved up here to be able to report
         # maxSizeResponseScopedPDU on error
         # (48 - maximum SNMPv3 header length)
-        maxSizeResponseScopedPDU = int(maxMessageSize) - len(securityParameters) - 48
+        maxSizeResponseScopedPDU = (int(maxMessageSize) -
+                                    len(securityParameters) - 48)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: securityParameters %s' % debug.hexdump(securityParameters))
+            'processIncomingMsg: securityParameters '
+            '%s' % debug.hexdump(securityParameters))
 
         # 3.2.1
         securityParameters, rest = decoder.decode(
-            securityParameters, asn1Spec=self.__securityParametersSpec
-        )
+            securityParameters, asn1Spec=self._securityParametersSpec)
 
-        debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: %s' % (securityParameters.prettyPrint(),))
+        debug.logger & debug.FLAG_SM and debug.logger(
+            'processIncomingMsg: %s' % (securityParameters.prettyPrint(),))
 
         if eoo.endOfOctets.isSameTypeWith(securityParameters):
             raise error.StatusInformation(errorIndication=errind.parseError)
 
         # 3.2.2
         msgAuthoritativeEngineId = securityParameters.getComponentByPosition(0)
+
         securityStateReference = self._cache.push(
             msgUserName=securityParameters.getComponentByPosition(3)
         )
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: cache write securityStateReference %s by msgUserName %s' % (
-                securityStateReference, securityParameters.getComponentByPosition(3)))
+            'processIncomingMsg: cache write securityStateReference %s by '
+            'msgUserName %s' % (securityStateReference,
+                                securityParameters.getComponentByPosition(3)))
 
         scopedPduData = msg.getComponentByPosition(3)
 
         # Used for error reporting
-        contextEngineId = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+        contextEngineId = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
         contextName = null
 
-        snmpEngineID = mibBuilder.importSymbols('__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
+        snmpEngineID = mibBuilder.importSymbols(
+            '__SNMP-FRAMEWORK-MIB', 'snmpEngineID')[0].syntax
 
         # 3.2.3
         if (msgAuthoritativeEngineId != snmpEngineID and
-                msgAuthoritativeEngineId not in self.__timeline):
+                msgAuthoritativeEngineId not in self._timeline):
+
             if (msgAuthoritativeEngineId and
                     4 < len(msgAuthoritativeEngineId) < 33):
                 # 3.2.3a - cloned user when request was sent
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: non-synchronized securityEngineID %r' % (msgAuthoritativeEngineId,))
+                    'processIncomingMsg: non-synchronized securityEngineID '
+                    '%r' % (msgAuthoritativeEngineId,))
+
             else:
                 # 3.2.3b
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: peer requested snmpEngineID discovery')
+
                 usmStatsUnknownEngineIDs, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownEngineIDs')
                 usmStatsUnknownEngineIDs.syntax += 1
+
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: null or malformed msgAuthoritativeEngineId')
+
                 pysnmpUsmDiscoverable, = mibBuilder.importSymbols(
                     '__PYSNMP-USM-MIB', 'pysnmpUsmDiscoverable')
+
                 if pysnmpUsmDiscoverable.syntax:
                     debug.logger & debug.FLAG_SM and debug.logger(
                         'processIncomingMsg: starting snmpEngineID discovery procedure')
@@ -631,10 +745,11 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     # Report original contextName
                     if scopedPduData.getName() != 'plaintext':
                         debug.logger & debug.FLAG_SM and debug.logger(
-                            'processIncomingMsg: scopedPduData not plaintext %s' % scopedPduData.prettyPrint())
+                            'processIncomingMsg: scopedPduData not plaintext '
+                            '%s' % scopedPduData.prettyPrint())
+
                         raise error.StatusInformation(
-                            errorIndication=errind.unknownEngineID
-                        )
+                            errorIndication=errind.unknownEngineID)
 
                     # 7.2.6.a.1
                     scopedPdu = scopedPduData.getComponent()
@@ -653,16 +768,18 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                     )
                 else:
-                    debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: will not discover EngineID')
+                    debug.logger & debug.FLAG_SM and debug.logger(
+                        'processIncomingMsg: will not discover EngineID')
+
                     # free securityStateReference XXX
                     raise error.StatusInformation(
-                        errorIndication=errind.unknownEngineID
-                    )
+                        errorIndication=errind.unknownEngineID)
 
         msgUserName = securityParameters.getComponentByPosition(3)
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: read from securityParams msgAuthoritativeEngineId %r msgUserName %r' % (
+            'processIncomingMsg: read from securityParams '
+            'msgAuthoritativeEngineId %r msgUserName %r' % (
                 msgAuthoritativeEngineId, msgUserName))
 
         if msgUserName:
@@ -673,16 +790,17 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                  usmUserAuthProtocol,
                  usmUserAuthKeyLocalized,
                  usmUserPrivProtocol,
-                 usmUserPrivKeyLocalized) = self.__getUserInfo(
+                 usmUserPrivKeyLocalized) = self._getUserInfo(
                     snmpEngine.msgAndPduDsp.mibInstrumController,
                     msgAuthoritativeEngineId, msgUserName
                 )
-                debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: read user info from LCD')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    'processIncomingMsg: read user info from LCD')
 
             except NoSuchInstanceError:
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: unknown securityEngineID %r msgUserName %r' % (
-                        msgAuthoritativeEngineId, msgUserName))
+                    'processIncomingMsg: unknown securityEngineID %r '
+                    'msgUserName %r' % (msgAuthoritativeEngineId, msgUserName))
 
                 usmStatsUnknownUserNames, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownUserNames')
@@ -701,10 +819,15 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                 )
 
             except PyAsn1Error as exc:
-                debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: %s' % exc)
-                snmpInGenErrs, = mibBuilder.importSymbols('__SNMPv2-MIB', 'snmpInGenErrs')
+                debug.logger & debug.FLAG_SM and debug.logger(
+                    'processIncomingMsg: %s' % exc)
+
+                snmpInGenErrs, = mibBuilder.importSymbols(
+                    '__SNMPv2-MIB', 'snmpInGenErrs')
                 snmpInGenErrs.syntax += 1
+
                 raise error.StatusInformation(errorIndication=errind.invalidMsg)
+
         else:
             # empty username used for engineID discovery
             usmUserName = usmUserSecurityName = null
@@ -713,11 +836,14 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             usmUserAuthKeyLocalized = usmUserPrivKeyLocalized = None
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: now have usmUserName %r usmUserSecurityName %r usmUserAuthProtocol %r usmUserPrivProtocol %r for msgUserName %r' % (
-                usmUserName, usmUserSecurityName, usmUserAuthProtocol, usmUserPrivProtocol, msgUserName))
+            'processIncomingMsg: now have usmUserName %r usmUserSecurityName '
+            '%r usmUserAuthProtocol %r usmUserPrivProtocol %r for msgUserName '
+            '%r' % (usmUserName, usmUserSecurityName, usmUserAuthProtocol,
+                    usmUserPrivProtocol, msgUserName))
 
         # 3.2.11 (moved up here to let Reports be authenticated & encrypted)
         self._cache.pop(securityStateReference)
+
         securityStateReference = self._cache.push(
             msgUserName=securityParameters.getComponentByPosition(3),
             usmUserSecurityName=usmUserSecurityName,
@@ -743,21 +869,24 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                  privKey=usmUserPrivKeyLocalized)
         )
         snmpEngine.observer.clearExecutionContext(
-            snmpEngine, 'rfc3414.processIncomingMsg'
-        )
+            snmpEngine, 'rfc3414.processIncomingMsg')
 
         # 3.2.5
         if msgAuthoritativeEngineId == snmpEngineID:
             # Authoritative SNMP engine: make sure securityLevel is sufficient
             badSecIndication = None
+
             if securityLevel == 3:
                 if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'authPriv wanted while auth not expected'
+
                 if usmUserPrivProtocol == nopriv.NoPriv.SERVICE_ID:
                     badSecIndication = 'authPriv wanted while priv not expected'
+
             elif securityLevel == 2:
                 if usmUserAuthProtocol == noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'authNoPriv wanted while auth not expected'
+
                 if usmUserPrivProtocol != nopriv.NoPriv.SERVICE_ID:
                     # 4 (discovery phase always uses authenticated messages)
                     if msgAuthoritativeEngineBoots or msgAuthoritativeEngineTime:
@@ -766,15 +895,20 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             elif securityLevel == 1:
                 if usmUserAuthProtocol != noauth.NoAuth.SERVICE_ID:
                     badSecIndication = 'noAuthNoPriv wanted while auth expected'
+
                 if usmUserPrivProtocol != nopriv.NoPriv.SERVICE_ID:
                     badSecIndication = 'noAuthNoPriv wanted while priv expected'
+
             if badSecIndication:
                 usmStatsUnsupportedSecLevels, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnsupportedSecLevels')
+
                 usmStatsUnsupportedSecLevels.syntax += 1
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: reporting inappropriate security level for user %s: %s' % (
-                        msgUserName, badSecIndication))
+                    'processIncomingMsg: reporting inappropriate security '
+                    'level for user %s: %s' % (msgUserName, badSecIndication))
+
                 raise error.StatusInformation(
                     errorIndication=errind.unsupportedSecurityLevel,
                     oid=usmStatsUnsupportedSecLevels.name,
@@ -791,22 +925,23 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         if securityLevel == 3 or securityLevel == 2:
             if usmUserAuthProtocol in self.AUTH_SERVICES:
                 authHandler = self.AUTH_SERVICES[usmUserAuthProtocol]
+
             else:
                 raise error.StatusInformation(
-                    errorIndication=errind.authenticationFailure
-                )
+                    errorIndication=errind.authenticationFailure)
 
             try:
                 authHandler.authenticateIncomingMsg(
                     usmUserAuthKeyLocalized,
                     securityParameters.getComponentByPosition(4),
-                    wholeMsg
-                )
+                    wholeMsg)
 
             except error.StatusInformation:
                 usmStatsWrongDigests, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsWrongDigests')
+
                 usmStatsWrongDigests.syntax += 1
+
                 raise error.StatusInformation(
                     errorIndication=errind.authenticationFailure,
                     oid=usmStatsWrongDigests.name,
@@ -819,62 +954,81 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                 )
 
-            debug.logger & debug.FLAG_SM and debug.logger('processIncomingMsg: incoming msg authenticated')
+            debug.logger & debug.FLAG_SM and debug.logger(
+                'processIncomingMsg: incoming msg authenticated')
 
             # synchronize time with authed peer
-            self.__timeline[msgAuthoritativeEngineId] = (
+            self._timeline[msgAuthoritativeEngineId] = (
                 securityParameters.getComponentByPosition(1),
                 securityParameters.getComponentByPosition(2),
                 securityParameters.getComponentByPosition(2),
                 int(time.time())
             )
 
-            timerResolution = snmpEngine.transportDispatcher is None and 1.0 or snmpEngine.transportDispatcher.getTimerResolution()
-            expireAt = int(self.__expirationTimer + 300 / timerResolution)
-            if expireAt not in self.__timelineExpQueue:
-                self.__timelineExpQueue[expireAt] = []
-            self.__timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
+            timerResolution = (snmpEngine.transportDispatcher is None and 1.0 or
+                               snmpEngine.transportDispatcher.getTimerResolution())
+
+            expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+            if expireAt not in self._timelineExpQueue:
+                self._timelineExpQueue[expireAt] = []
+
+            self._timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
 
             debug.logger & debug.FLAG_SM and debug.logger(
-                'processIncomingMsg: store timeline for securityEngineID %r' % (msgAuthoritativeEngineId,))
+                'processIncomingMsg: store timeline for securityEngineID '
+                '%r' % (msgAuthoritativeEngineId,))
 
         # 3.2.7
         if securityLevel == 3 or securityLevel == 2:
             if msgAuthoritativeEngineId == snmpEngineID:
                 # Authoritative SNMP engine: use local notion (SF bug #1649032)
-                (snmpEngineBoots,
-                 snmpEngineTime) = mibBuilder.importSymbols(
+                snmpEngineBoots, snmpEngineTime = mibBuilder.importSymbols(
                     '__SNMP-FRAMEWORK-MIB', 'snmpEngineBoots', 'snmpEngineTime')
+
                 snmpEngineBoots = snmpEngineBoots.syntax
                 snmpEngineTime = snmpEngineTime.syntax.clone()
+
                 idleTime = 0
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: read snmpEngineBoots (%s), snmpEngineTime (%s) from LCD' % (
+                    'processIncomingMsg: read snmpEngineBoots (%s), '
+                    'snmpEngineTime (%s) from LCD' % (
                         snmpEngineBoots, snmpEngineTime))
+
             else:
                 # Non-authoritative SNMP engine: use cached estimates
-                if msgAuthoritativeEngineId in self.__timeline:
+                if msgAuthoritativeEngineId in self._timeline:
                     (snmpEngineBoots, snmpEngineTime,
                      latestReceivedEngineTime,
-                     latestUpdateTimestamp) = self.__timeline[
+                     latestUpdateTimestamp) = self._timeline[
                         msgAuthoritativeEngineId
                     ]
+
                     # time passed since last talk with this SNMP engine
                     idleTime = int(time.time()) - latestUpdateTimestamp
+
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        'processIncomingMsg: read timeline snmpEngineBoots %s snmpEngineTime %s for msgAuthoritativeEngineId %r, idle time %s secs' % (
-                            snmpEngineBoots, snmpEngineTime, msgAuthoritativeEngineId, idleTime))
+                        'processIncomingMsg: read timeline snmpEngineBoots %s '
+                        'snmpEngineTime %s for msgAuthoritativeEngineId %r, '
+                        'idle time %s secs' % (snmpEngineBoots, snmpEngineTime,
+                                               msgAuthoritativeEngineId,
+                                               idleTime))
                 else:
                     raise error.ProtocolError('Peer SNMP engine info missing')
 
             # 3.2.7a
             if msgAuthoritativeEngineId == snmpEngineID:
+
                 if (snmpEngineBoots == 2147483647 or
                         snmpEngineBoots != msgAuthoritativeEngineBoots or
-                        abs(idleTime + int(snmpEngineTime) - int(msgAuthoritativeEngineTime)) > 150):
+                        (abs(idleTime + int(snmpEngineTime)
+                             - int(msgAuthoritativeEngineTime))) > 150):
+
                     usmStatsNotInTimeWindows, = mibBuilder.importSymbols(
                         '__SNMP-USER-BASED-SM-MIB', 'usmStatsNotInTimeWindows')
                     usmStatsNotInTimeWindows.syntax += 1
+
                     raise error.StatusInformation(
                         errorIndication=errind.notInTimeWindow,
                         oid=usmStatsNotInTimeWindows.name,
@@ -886,6 +1040,7 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                         msgUserName=msgUserName,
                         maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                     )
+
             # 3.2.7b
             else:
                 # 3.2.7b.1
@@ -893,48 +1048,60 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                 if (msgAuthoritativeEngineBoots > snmpEngineBoots or
                         msgAuthoritativeEngineBoots == snmpEngineBoots and
                         msgAuthoritativeEngineTime > latestReceivedEngineTime):
-                    self.__timeline[msgAuthoritativeEngineId] = (
+                    self._timeline[msgAuthoritativeEngineId] = (
                         msgAuthoritativeEngineBoots,
                         msgAuthoritativeEngineTime,
                         msgAuthoritativeEngineTime,
                         int(time.time())
                     )
 
-                    timerResolution = snmpEngine.transportDispatcher is None and 1.0 or snmpEngine.transportDispatcher.getTimerResolution()
-                    expireAt = int(self.__expirationTimer + 300 / timerResolution)
-                    if expireAt not in self.__timelineExpQueue:
-                        self.__timelineExpQueue[expireAt] = []
-                    self.__timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
+                    timerResolution = (
+                            snmpEngine.transportDispatcher is None and 1.0 or
+                           snmpEngine.transportDispatcher.getTimerResolution())
+
+                    expireAt = int(self._expirationTimer + 300 / timerResolution)
+
+                    if expireAt not in self._timelineExpQueue:
+                        self._timelineExpQueue[expireAt] = []
+
+                    self._timelineExpQueue[expireAt].append(msgAuthoritativeEngineId)
 
                     debug.logger & debug.FLAG_SM and debug.logger(
-                        'processIncomingMsg: stored timeline msgAuthoritativeEngineBoots %s msgAuthoritativeEngineTime %s for msgAuthoritativeEngineId %r' % (
-                            msgAuthoritativeEngineBoots, msgAuthoritativeEngineTime, msgAuthoritativeEngineId))
+                        'processIncomingMsg: stored timeline '
+                        'msgAuthoritativeEngineBoots %s '
+                        'msgAuthoritativeEngineTime %s for '
+                        'msgAuthoritativeEngineId '
+                        '%r' % (msgAuthoritativeEngineBoots,
+                                msgAuthoritativeEngineTime,
+                                msgAuthoritativeEngineId))
 
                 # 3.2.7b.2
                 if (snmpEngineBoots == 2147483647 or
                         msgAuthoritativeEngineBoots < snmpEngineBoots or
                         msgAuthoritativeEngineBoots == snmpEngineBoots and
-                        abs(idleTime + int(snmpEngineTime) - int(msgAuthoritativeEngineTime)) > 150):
+                        (abs(idleTime + int(snmpEngineTime)
+                             - int(msgAuthoritativeEngineTime))) > 150):
+
                     raise error.StatusInformation(
                         errorIndication=errind.notInTimeWindow,
-                        msgUserName=msgUserName
-                    )
+                        msgUserName=msgUserName)
 
         # 3.2.8a
         if securityLevel == 3:
             if usmUserPrivProtocol in self.PRIV_SERVICES:
                 privHandler = self.PRIV_SERVICES[usmUserPrivProtocol]
+
             else:
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
+
             encryptedPDU = scopedPduData.getComponentByPosition(1)
+
             if encryptedPDU is None:  # no ciphertext
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
             try:
                 decryptedData = privHandler.decryptData(
@@ -942,15 +1109,17 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     (securityParameters.getComponentByPosition(1),
                      securityParameters.getComponentByPosition(2),
                      securityParameters.getComponentByPosition(5)),
-                    encryptedPDU
-                )
+                    encryptedPDU)
+
                 debug.logger & debug.FLAG_SM and debug.logger(
-                    'processIncomingMsg: PDU deciphered into %s' % debug.hexdump(decryptedData))
+                    'processIncomingMsg: PDU deciphered into '
+                    '%s' % debug.hexdump(decryptedData))
 
             except error.StatusInformation:
                 usmStatsDecryptionErrors, = mibBuilder.importSymbols(
                     '__SNMP-USER-BASED-SM-MIB', 'usmStatsDecryptionErrors')
                 usmStatsDecryptionErrors.syntax += 1
+
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
                     oid=usmStatsDecryptionErrors.name,
@@ -962,31 +1131,32 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
                     msgUserName=msgUserName,
                     maxSizeResponseScopedPDU=maxSizeResponseScopedPDU
                 )
-            scopedPduSpec = scopedPduData.setComponentByPosition(0).getComponentByPosition(0)
+            scopedPduSpec = scopedPduData.setComponentByPosition(
+                0).getComponentByPosition(0)
+
             try:
                 scopedPDU, rest = decoder.decode(decryptedData, asn1Spec=scopedPduSpec)
 
             except PyAsn1Error as exc:
                 debug.logger & debug.FLAG_SM and debug.logger(
                     'processIncomingMsg: scopedPDU decoder failed %s' % exc)
+
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
             if eoo.endOfOctets.isSameTypeWith(scopedPDU):
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
+
         else:
             # 3.2.8b
             scopedPDU = scopedPduData.getComponentByPosition(0)
             if scopedPDU is None:  # no plaintext
                 raise error.StatusInformation(
                     errorIndication=errind.decryptionError,
-                    msgUserName=msgUserName
-                )
+                    msgUserName=msgUserName)
 
         debug.logger & debug.FLAG_SM and debug.logger(
             'processIncomingMsg: scopedPDU decoded %s' % scopedPDU.prettyPrint())
@@ -995,7 +1165,8 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         securityName = usmUserSecurityName
 
         debug.logger & debug.FLAG_SM and debug.logger(
-            'processIncomingMsg: cached msgUserName %s info by securityStateReference %s' % (
+            'processIncomingMsg: cached msgUserName %s info by '
+            'securityStateReference %s' % (
                 msgUserName, securityStateReference))
 
         # Delayed to include details
@@ -1003,6 +1174,7 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
             usmStatsUnknownUserNames, = mibBuilder.importSymbols(
                 '__SNMP-USER-BASED-SM-MIB', 'usmStatsUnknownUserNames')
             usmStatsUnknownUserNames.syntax += 1
+
             raise error.StatusInformation(
                 errorIndication=errind.unknownSecurityName,
                 oid=usmStatsUnknownUserNames.name,
@@ -1021,14 +1193,18 @@ class SnmpUSMSecurityModel(AbstractSecurityModel):
         return (msgAuthoritativeEngineId, securityName, scopedPDU,
                 maxSizeResponseScopedPDU, securityStateReference)
 
-    def __expireTimelineInfo(self):
-        if self.__expirationTimer in self.__timelineExpQueue:
-            for engineIdKey in self.__timelineExpQueue[self.__expirationTimer]:
-                if engineIdKey in self.__timeline:
-                    del self.__timeline[engineIdKey]
-                    debug.logger & debug.FLAG_SM and debug.logger('__expireTimelineInfo: expiring %r' % (engineIdKey,))
-            del self.__timelineExpQueue[self.__expirationTimer]
-        self.__expirationTimer += 1
+    def _expireTimelineInfo(self):
+        if self._expirationTimer in self._timelineExpQueue:
+
+            for engineIdKey in self._timelineExpQueue[self._expirationTimer]:
+                if engineIdKey in self._timeline:
+                    del self._timeline[engineIdKey]
+                    debug.logger & debug.FLAG_SM and debug.logger(
+                        '__expireTimelineInfo: expiring %r' % (engineIdKey,))
+
+            del self._timelineExpQueue[self._expirationTimer]
+
+        self._expirationTimer += 1
 
     def receiveTimerTick(self, snmpEngine, timeNow):
-        self.__expireTimelineInfo()
+        self._expireTimelineInfo()
diff --git a/pysnmp/proto/secmod/rfc3826/priv/aes.py b/pysnmp/proto/secmod/rfc3826/priv/aes.py
index 56f69280..d000f8ed 100644
--- a/pysnmp/proto/secmod/rfc3826/priv/aes.py
+++ b/pysnmp/proto/secmod/rfc3826/priv/aes.py
@@ -38,66 +38,85 @@ class Aes(base.AbstractEncryptionService):
     local_int = random.randrange(0, 0xffffffffffffffff)
 
     # 3.1.2.1
-    def __getEncryptionKey(self, privKey, snmpEngineBoots, snmpEngineTime):
-        salt = [self.local_int >> 56 & 0xff,
-                self.local_int >> 48 & 0xff,
-                self.local_int >> 40 & 0xff,
-                self.local_int >> 32 & 0xff,
-                self.local_int >> 24 & 0xff,
-                self.local_int >> 16 & 0xff,
-                self.local_int >> 8 & 0xff,
-                self.local_int & 0xff]
+    def _getEncryptionKey(self, privKey, snmpEngineBoots, snmpEngineTime):
+        salt = [
+            self.local_int >> 56 & 0xff,
+            self.local_int >> 48 & 0xff,
+            self.local_int >> 40 & 0xff,
+            self.local_int >> 32 & 0xff,
+            self.local_int >> 24 & 0xff,
+            self.local_int >> 16 & 0xff,
+            self.local_int >> 8 & 0xff,
+            self.local_int & 0xff
+        ]
 
         if self.local_int == 0xffffffffffffffff:
             self.local_int = 0
+
         else:
             self.local_int += 1
 
-        return self.__getDecryptionKey(privKey, snmpEngineBoots, snmpEngineTime, salt) + (
-        univ.OctetString(salt).asOctets(),)
+        key, iv = self._getDecryptionKey(
+            privKey, snmpEngineBoots, snmpEngineTime, salt)
+
+        return key, iv, univ.OctetString(salt).asOctets()
+
+    def _getDecryptionKey(self, privKey, snmpEngineBoots,
+                          snmpEngineTime, salt):
 
-    def __getDecryptionKey(self, privKey, snmpEngineBoots,
-                           snmpEngineTime, salt):
         snmpEngineBoots, snmpEngineTime, salt = (
-            int(snmpEngineBoots), int(snmpEngineTime), salt
-        )
+            int(snmpEngineBoots), int(snmpEngineTime), salt)
+
+        iv = [
+            snmpEngineBoots >> 24 & 0xff,
+            snmpEngineBoots >> 16 & 0xff,
+            snmpEngineBoots >> 8 & 0xff,
+            snmpEngineBoots & 0xff,
+            snmpEngineTime >> 24 & 0xff,
+            snmpEngineTime >> 16 & 0xff,
+            snmpEngineTime >> 8 & 0xff,
+            snmpEngineTime & 0xff
+        ]
 
-        iv = [snmpEngineBoots >> 24 & 0xff,
-              snmpEngineBoots >> 16 & 0xff,
-              snmpEngineBoots >> 8 & 0xff,
-              snmpEngineBoots & 0xff,
-              snmpEngineTime >> 24 & 0xff,
-              snmpEngineTime >> 16 & 0xff,
-              snmpEngineTime >> 8 & 0xff,
-              snmpEngineTime & 0xff] + salt
+        iv += salt
 
-        return privKey[:self.KEY_SIZE].asOctets(), univ.OctetString(iv).asOctets()
+        key = privKey[:self.KEY_SIZE].asOctets()
+        iv = univ.OctetString(iv).asOctets()
+
+        return key, iv
 
     def hashPassphrase(self, authProtocol, privKey):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         return localkey.hashPassphrase(privKey, hashAlgo)
 
     def localizeKey(self, authProtocol, privKey, snmpEngineID):
         if authProtocol == hmacmd5.HmacMd5.SERVICE_ID:
             hashAlgo = md5
+
         elif authProtocol == hmacsha.HmacSha.SERVICE_ID:
             hashAlgo = sha1
+
         elif authProtocol in hmacsha2.HmacSha2.HASH_ALGORITHM:
             hashAlgo = hmacsha2.HmacSha2.HASH_ALGORITHM[authProtocol]
+
         else:
             raise error.ProtocolError(
-                'Unknown auth protocol %s' % (authProtocol,)
-            )
+                'Unknown auth protocol %s' % (authProtocol,))
+
         localPrivKey = localkey.localizeKey(privKey, snmpEngineID, hashAlgo)
+
         return localPrivKey[:self.KEY_SIZE]
 
     # 3.2.4.1
@@ -105,21 +124,20 @@ class Aes(base.AbstractEncryptionService):
         snmpEngineBoots, snmpEngineTime, salt = privParameters
 
         # 3.3.1.1
-        aesKey, iv, salt = self.__getEncryptionKey(
-            encryptKey, snmpEngineBoots, snmpEngineTime
-        )
+        aesKey, iv, salt = self._getEncryptionKey(
+            encryptKey, snmpEngineBoots, snmpEngineTime)
 
         # 3.3.1.3
         # PyCrypto seems to require padding
-        dataToEncrypt = dataToEncrypt + univ.OctetString((0,) * (16 - len(dataToEncrypt) % 16)).asOctets()
+        padding = univ.OctetString((0,) * (16 - len(dataToEncrypt) % 16))
+        dataToEncrypt += padding
 
         try:
-            ciphertext = aes.encrypt(dataToEncrypt, aesKey, iv)
+            ciphertext = aes.encrypt(dataToEncrypt.asOctets(), aesKey, iv)
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
 
         # 3.3.1.4
         return univ.OctetString(ciphertext), univ.OctetString(salt)
@@ -131,16 +149,15 @@ class Aes(base.AbstractEncryptionService):
         # 3.3.2.1
         if len(salt) != 8:
             raise error.StatusInformation(
-                errorIndication=errind.decryptionError
-            )
+                errorIndication=errind.decryptionError)
 
         # 3.3.2.3
-        aesKey, iv = self.__getDecryptionKey(
-            decryptKey, snmpEngineBoots, snmpEngineTime, salt
-        )
+        aesKey, iv = self._getDecryptionKey(
+            decryptKey, snmpEngineBoots, snmpEngineTime, salt)
 
         # PyCrypto seems to require padding
-        encryptedData = encryptedData + univ.OctetString((0,) * (16 - len(encryptedData) % 16)).asOctets()
+        padding = univ.OctetString((0,) * (16 - len(encryptedData) % 16))
+        encryptedData += padding
 
         try:
             # 3.3.2.4-6
@@ -148,5 +165,4 @@ class Aes(base.AbstractEncryptionService):
 
         except PysnmpCryptoError:
             raise error.StatusInformation(
-                errorIndication=errind.unsupportedPrivProtocol
-            )
+                errorIndication=errind.unsupportedPrivProtocol)
diff --git a/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py b/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
index 11dd79b3..267db682 100644
--- a/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
+++ b/pysnmp/proto/secmod/rfc7860/auth/hmacsha2.py
@@ -19,19 +19,26 @@ except ImportError:
 
     sha224 = sha256 = sha384 = sha512 = NotAvailable()
 
-from pyasn1.type import univ
 from pysnmp.proto.secmod.rfc3414.auth import base
 from pysnmp.proto.secmod.rfc3414 import localkey
 from pysnmp.proto import errind, error
 
+from pyasn1.type import univ
 
 # 7.2.4
 
 class HmacSha2(base.AbstractAuthenticationService):
-    SHA224_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 4)  # usmHMAC128SHA224AuthProtocol
-    SHA256_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 5)  # usmHMAC192SHA256AuthProtocol
-    SHA384_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 6)  # usmHMAC256SHA384AuthProtocol
-    SHA512_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 7)  # usmHMAC384SHA512AuthProtocol
+    # usmHMAC128SHA224AuthProtocol
+    SHA224_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 4)
+
+    # usmHMAC192SHA256AuthProtocol
+    SHA256_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 5)
+
+    # usmHMAC256SHA384AuthProtocol
+    SHA384_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 6)
+
+    # usmHMAC384SHA512AuthProtocol
+    SHA512_SERVICE_ID = (1, 3, 6, 1, 6, 3, 10, 1, 1, 7)
 
     KEY_LENGTH = {
         SHA224_SERVICE_ID: 28,
@@ -59,39 +66,43 @@ class HmacSha2(base.AbstractAuthenticationService):
     
     def __init__(self, oid):
         if oid not in self.HASH_ALGORITHM:
-            raise error.ProtocolError('No SHA-2 authentication algorithm %s available' % (oid,))
-        self.__hashAlgo = self.HASH_ALGORITHM[oid]
-        self.__digestLength = self.DIGEST_LENGTH[oid]
-        self.__placeHolder = univ.OctetString((0,) * self.__digestLength).asOctets()
+            raise error.ProtocolError(
+                'No SHA-2 authentication algorithm %s available' % (oid,))
+
+        self._hashAlgo = self.HASH_ALGORITHM[oid]
+        self._digestLength = self.DIGEST_LENGTH[oid]
+        self._placeHolder = univ.OctetString(
+            (0,) * self._digestLength).asOctets()
 
     def hashPassphrase(self, authKey):
-        return localkey.hashPassphrase(authKey, self.__hashAlgo)
+        return localkey.hashPassphrase(authKey, self._hashAlgo)
 
     def localizeKey(self, authKey, snmpEngineID):
-        return localkey.localizeKey(authKey, snmpEngineID, self.__hashAlgo)
+        return localkey.localizeKey(authKey, snmpEngineID, self._hashAlgo)
 
     @property
     def digestLength(self):
-        return self.__digestLength
+        return self._digestLength
 
     # 7.3.1
     def authenticateOutgoingMsg(self, authKey, wholeMsg):
         # 7.3.1.1
-        location = wholeMsg.find(self.__placeHolder)
+        location = wholeMsg.find(self._placeHolder)
         if location == -1:
-            raise error.ProtocolError('Can\'t locate digest placeholder')
+            raise error.ProtocolError('Cannot locate digest placeholder')
+
         wholeHead = wholeMsg[:location]
-        wholeTail = wholeMsg[location + self.__digestLength:]
+        wholeTail = wholeMsg[location + self._digestLength:]
 
         # 7.3.1.2, 7.3.1.3
         try:
-            mac = hmac.new(authKey.asOctets(), wholeMsg, self.__hashAlgo)
+            mac = hmac.new(authKey.asOctets(), wholeMsg, self._hashAlgo)
 
         except errind.ErrorIndication as exc:
             raise error.StatusInformation(errorIndication=exc)
 
         # 7.3.1.4
-        mac = mac.digest()[:self.__digestLength]
+        mac = mac.digest()[:self._digestLength]
 
         # 7.3.1.5 & 6
         return wholeHead + mac + wholeTail
@@ -99,33 +110,32 @@ class HmacSha2(base.AbstractAuthenticationService):
     # 7.3.2
     def authenticateIncomingMsg(self, authKey, authParameters, wholeMsg):
         # 7.3.2.1 & 2
-        if len(authParameters) != self.__digestLength:
+        if len(authParameters) != self._digestLength:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationError
-            )
+                errorIndication=errind.authenticationError)
 
         # 7.3.2.3
         location = wholeMsg.find(authParameters.asOctets())
         if location == -1:
-            raise error.ProtocolError('Can\'t locate digest in wholeMsg')
+            raise error.ProtocolError('Cannot locate digest in wholeMsg')
+
         wholeHead = wholeMsg[:location]
-        wholeTail = wholeMsg[location + self.__digestLength:]
-        authenticatedWholeMsg = wholeHead + self.__placeHolder + wholeTail
+        wholeTail = wholeMsg[location + self._digestLength:]
+        authenticatedWholeMsg = wholeHead + self._placeHolder + wholeTail
 
         # 7.3.2.4
         try:
-            mac = hmac.new(authKey.asOctets(), authenticatedWholeMsg, self.__hashAlgo)
+            mac = hmac.new(authKey.asOctets(), authenticatedWholeMsg, self._hashAlgo)
 
         except errind.ErrorIndication as exc:
             raise error.StatusInformation(errorIndication=exc)
 
         # 7.3.2.5
-        mac = mac.digest()[:self.__digestLength]
+        mac = mac.digest()[:self._digestLength]
 
         # 7.3.2.6
         if mac != authParameters:
             raise error.StatusInformation(
-                errorIndication=errind.authenticationFailure
-            )
+                errorIndication=errind.authenticationFailure)
 
         return authenticatedWholeMsg
diff --git a/pysnmp/smi/builder.py b/pysnmp/smi/builder.py
index 9d75732b..513bc19a 100644
--- a/pysnmp/smi/builder.py
+++ b/pysnmp/smi/builder.py
@@ -33,25 +33,31 @@ from pysnmp import debug
 class __AbstractMibSource(object):
     def __init__(self, srcName):
         self._srcName = srcName
-        self.__magic = imp.get_magic()
-        self.__sfx = {}
-        self.__inited = None
+        self._magic = imp.get_magic()
+        self._sfx = {}
+        self._inited = None
+
         for sfx, mode, typ in imp.get_suffixes():
-            if typ not in self.__sfx:
-                self.__sfx[typ] = []
-            self.__sfx[typ].append((sfx, len(sfx), mode))
-        debug.logger & debug.FLAG_BLD and debug.logger('trying %s' % self)
+            if typ not in self._sfx:
+                self._sfx[typ] = []
+
+            self._sfx[typ].append((sfx, len(sfx), mode))
+
+        debug.logger & debug.FLAG_BLD and debug.logger(
+            'trying %s' % self)
 
     def __repr__(self):
         return '%s(%r)' % (self.__class__.__name__, self._srcName)
 
     def _uniqNames(self, files):
         u = set()
+
         for f in files:
             if f.startswith('__init__.'):
                 continue
+
             for typ in (imp.PY_SOURCE, imp.PY_COMPILED):
-                for sfx, sfxLen, mode in self.__sfx[typ]:
+                for sfx, sfxLen, mode in self._sfx[typ]:
                     if f[-sfxLen:] == sfx:
                         u.add(f[:-sfxLen])
         return tuple(u)
@@ -59,18 +65,23 @@ class __AbstractMibSource(object):
     # MibSource API follows
 
     def fullPath(self, f='', sfx=''):
-        return self._srcName + (f and (os.sep + f + sfx) or '')
+        if f:
+            return os.path.join(self._srcName, f) + sfx
+
+        return self._srcName
 
     def init(self):
-        if self.__inited is None:
-            self.__inited = self._init()
-            if self.__inited is self:
-                self.__inited = True
-        if self.__inited is True:
+        if self._inited is None:
+            self._inited = self._init()
+
+            if self._inited is self:
+                self._inited = True
+
+        if self._inited is True:
             return self
 
         else:
-            return self.__inited
+            return self._inited
 
     def listdir(self):
         return self._listdir()
@@ -78,54 +89,62 @@ class __AbstractMibSource(object):
     def read(self, f):
         pycTime = pyTime = -1
 
-        for pycSfx, pycSfxLen, pycMode in self.__sfx[imp.PY_COMPILED]:
+        for pycSfx, pycSfxLen, pycMode in self._sfx[imp.PY_COMPILED]:
+
+            pycFile = f + pycSfx
+
             try:
-                pycData, pycPath = self._getData(f + pycSfx, pycMode)
+                pycData, pycPath = self._getData(pycFile, pycMode)
 
             except IOError as exc:
                 if ENOENT == -1 or exc.errno == ENOENT:
                     debug.logger & debug.FLAG_BLD and debug.logger(
-                        'file %s access error: %s' % (f + pycSfx, exc)
-                    )
+                        'file %s access error: %s' % (pycFile, exc))
 
                 else:
-                    raise error.MibLoadError('MIB file %s access error: %s' % (f + pycSfx, exc))
+                    raise error.MibLoadError(
+                        'MIB file %s access error: %s' % (pycFile, exc))
 
             else:
-                if self.__magic == pycData[:4]:
+                if self._magic == pycData[:4]:
                     pycData = pycData[4:]
                     pycTime = struct.unpack('<L', pycData[:4])[0]
                     pycData = pycData[4:]
+
                     debug.logger & debug.FLAG_BLD and debug.logger(
-                        'file %s mtime %d' % (pycPath, pycTime)
-                    )
+                        'file %s mtime %d' % (pycPath, pycTime))
+
                     break
 
                 else:
-                    debug.logger & debug.FLAG_BLD and debug.logger('bad magic in %s' % pycPath)
+                    debug.logger & debug.FLAG_BLD and debug.logger(
+                        'bad magic in %s' % pycPath)
+
+        for pySfx, pySfxLen, pyMode in self._sfx[imp.PY_SOURCE]:
+            pyFile = f + pySfx
 
-        for pySfx, pySfxLen, pyMode in self.__sfx[imp.PY_SOURCE]:
             try:
-                pyTime = self._getTimestamp(f + pySfx)
+                pyTime = self._getTimestamp(pyFile)
 
             except IOError as exc:
                 if ENOENT == -1 or exc.errno == ENOENT:
                     debug.logger & debug.FLAG_BLD and debug.logger(
-                        'file %s access error: %s' % (f + pySfx, exc)
-                    )
+                        'file %s access error: %s' % (pyFile, exc))
 
                 else:
-                    raise error.MibLoadError('MIB file %s access error: %s' % (f + pySfx, exc))
+                    raise error.MibLoadError(
+                        'MIB file %s access error: %s' % (pyFile, exc))
 
             else:
-                debug.logger & debug.FLAG_BLD and debug.logger('file %s mtime %d' % (f + pySfx, pyTime))
+                debug.logger & debug.FLAG_BLD and debug.logger(
+                    'file %s mtime %d' % (pyFile, pyTime))
                 break
 
         if pycTime != -1 and pycTime >= pyTime:
             return marshal.loads(pycData), pycSfx
 
         if pyTime != -1:
-            modData, pyPath = self._getData(f + pySfx, pyMode)
+            modData, pyPath = self._getData(pyFile, pyMode)
             return compile(modData, pyPath, 'exec'), pyPath
 
         raise IOError(ENOENT, 'No suitable module found', f)
@@ -147,16 +166,21 @@ class __AbstractMibSource(object):
 class ZipMibSource(__AbstractMibSource):
     def _init(self):
         try:
-            p = __import__(self._srcName, globals(), locals(), ['__init__'])
-            if hasattr(p, '__loader__') and hasattr(p.__loader__, '_files'):
-                self.__loader = p.__loader__
+            mod = __import__(
+                self._srcName, globals(), locals(), ['__init__'])
+
+            if (hasattr(mod, '__loader__') and
+                    hasattr(mod.__loader__, '_files')):
+                self.__loader = mod.__loader__
                 self._srcName = self._srcName.replace('.', os.sep)
                 return self
-            elif hasattr(p, '__file__'):
+
+            elif hasattr(mod, '__file__'):
                 # Dir relative to PYTHONPATH
-                return DirMibSource(os.path.split(p.__file__)[0]).init()
+                return DirMibSource(os.path.split(mod.__file__)[0]).init()
+
             else:
-                raise error.MibLoadError('%s access error' % (p,))
+                raise error.MibLoadError('%s access error' % (mod,))
 
         except ImportError:
             # Dir relative to CWD
@@ -176,33 +200,40 @@ class ZipMibSource(__AbstractMibSource):
         return time.mktime(t)
 
     def _listdir(self):
-        l = []
+        dirs = []
+
         # noinspection PyProtectedMember
-        for f in self.__loader._files.keys():
-            d, f = os.path.split(f)
-            if d == self._srcName:
-                l.append(f)
-        return tuple(self._uniqNames(l))
+        for path in self.__loader._files:
+            dr, fl = os.path.split(path)
+            if dr == self._srcName:
+                dirs.append(fl)
+
+        return tuple(self._uniqNames(dirs))
 
     def _getTimestamp(self, f):
-        p = os.path.join(self._srcName, f)
+        path = os.path.join(self._srcName, f)
+
         # noinspection PyProtectedMember
-        if p in self.__loader._files:
+        if path in self.__loader._files:
             # noinspection PyProtectedMember
             return self._parseDosTime(
-                self.__loader._files[p][6], self.__loader._files[p][5]
+                self.__loader._files[path][6], self.__loader._files[path][5]
             )
+
         else:
-            raise IOError(ENOENT, 'No such file in ZIP archive', p)
+            raise IOError(ENOENT, 'No such file in ZIP archive', path)
 
     def _getData(self, f, mode=None):
-        p = os.path.join(self._srcName, f)
+        path = os.path.join(self._srcName, f)
+
         try:
-            return self.__loader.get_data(p), p
+            return self.__loader.get_data(path), path
 
         # ZIP code seems to return all kinds of errors
         except Exception as exc:
-            raise IOError(ENOENT, 'File or ZIP archive %s access error: %s' % (p, exc))
+            raise IOError(
+                ENOENT, 'File or ZIP archive %s access '
+                        'error: %s' % (path, exc))
 
 
 class DirMibSource(__AbstractMibSource):
@@ -213,33 +244,35 @@ class DirMibSource(__AbstractMibSource):
     def _listdir(self):
         try:
             return self._uniqNames(os.listdir(self._srcName))
+
         except OSError as exc:
             debug.logger & debug.FLAG_BLD and debug.logger(
                 'listdir() failed for %s: %s' % (self._srcName, exc))
             return ()
 
     def _getTimestamp(self, f):
-        p = os.path.join(self._srcName, f)
+        path = os.path.join(self._srcName, f)
         try:
-            return os.stat(p)[8]
+            return os.stat(path)[8]
         except OSError as exc:
-            raise IOError(ENOENT, 'No such file: %s' % exc, p)
+            raise IOError(ENOENT, 'No such file: %s' % exc, path)
+
+    def _getData(self, fl, mode):
+        path = os.path.join(self._srcName, '*')
 
-    def _getData(self, f, mode):
-        p = os.path.join(self._srcName, '*')
         try:
-            if f in os.listdir(self._srcName):  # make FS case-sensitive
-                p = os.path.join(self._srcName, f)
-                fp = open(p, mode)
+            if fl in os.listdir(self._srcName):  # make FS case-sensitive
+                path = os.path.join(self._srcName, fl)
+                fp = open(path, mode)
                 data = fp.read()
                 fp.close()
-                return data, p
+                return data, path
 
         except (IOError, OSError) as exc:
-            msg = 'File or directory %s access error: %s' % (p, exc)
+            msg = 'File or directory %s access error: %s' % (path, exc)
 
         else:
-            msg = 'No such file or directory: %s' % p
+            msg = 'No such file or directory: %s' % path
 
         raise IOError(ENOENT, msg)
 
@@ -260,91 +293,108 @@ class MibBuilder(object):
 
     def __init__(self):
         self.lastBuildId = self._autoName = 0
+
         sources = []
+
         for ev in 'PYSNMP_MIB_PKGS', 'PYSNMP_MIB_DIRS', 'PYSNMP_MIB_DIR':
             if ev in os.environ:
                 for m in os.environ[ev].split(os.pathsep):
                     sources.append(ZipMibSource(m))
+
         if not sources and self.DEFAULT_MISC_MIBS:
             for m in self.DEFAULT_MISC_MIBS.split(os.pathsep):
                 sources.append(ZipMibSource(m))
+
         for m in self.DEFAULT_CORE_MIBS.split(os.pathsep):
             sources.insert(0, ZipMibSource(m))
+
         self.mibSymbols = {}
-        self.__mibSources = []
-        self.__modSeen = {}
-        self.__modPathsSeen = set()
-        self.__mibCompiler = None
+        self._mibSources = []
+        self._modSeen = {}
+        self._modPathsSeen = set()
+        self._mibCompiler = None
+
         self.setMibSources(*sources)
 
     # MIB compiler management
 
     def getMibCompiler(self):
-        return self.__mibCompiler
+        return self._mibCompiler
 
     def setMibCompiler(self, mibCompiler, destDir):
         self.addMibSources(DirMibSource(destDir))
-        self.__mibCompiler = mibCompiler
+        self._mibCompiler = mibCompiler
         return self
 
     # MIB modules management
 
     def addMibSources(self, *mibSources):
-        self.__mibSources.extend([s.init() for s in mibSources])
-        debug.logger & debug.FLAG_BLD and debug.logger('addMibSources: new MIB sources %s' % (self.__mibSources,))
+        self._mibSources.extend([s.init() for s in mibSources])
+
+        debug.logger & debug.FLAG_BLD and debug.logger(
+            'addMibSources: new MIB sources %s' % (self._mibSources,))
 
     def setMibSources(self, *mibSources):
-        self.__mibSources = [s.init() for s in mibSources]
-        debug.logger & debug.FLAG_BLD and debug.logger('setMibSources: new MIB sources %s' % (self.__mibSources,))
+        self._mibSources = [s.init() for s in mibSources]
+
+        debug.logger & debug.FLAG_BLD and debug.logger(
+            'setMibSources: new MIB sources %s' % (self._mibSources,))
 
     def getMibSources(self):
-        return tuple(self.__mibSources)
+        return tuple(self._mibSources)
 
     def loadModule(self, modName, **userCtx):
         """Load and execute MIB modules as Python code"""
-        for mibSource in self.__mibSources:
-            debug.logger & debug.FLAG_BLD and debug.logger('loadModule: trying %s at %s' % (modName, mibSource))
+        for mibSource in self._mibSources:
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'loadModule: trying %s at %s' % (modName, mibSource))
+
             try:
                 codeObj, sfx = mibSource.read(modName)
 
             except IOError as exc:
                 debug.logger & debug.FLAG_BLD and debug.logger(
-                    'loadModule: read %s from %s failed: %s' % (modName, mibSource, exc))
+                    'loadModule: read %s from %s failed: '
+                    '%s' % (modName, mibSource, exc))
                 continue
 
             modPath = mibSource.fullPath(modName, sfx)
 
-            if modPath in self.__modPathsSeen:
-                debug.logger & debug.FLAG_BLD and debug.logger('loadModule: seen %s' % modPath)
+            if modPath in self._modPathsSeen:
+                debug.logger & debug.FLAG_BLD and debug.logger(
+                    'loadModule: seen %s' % modPath)
                 break
 
             else:
-                self.__modPathsSeen.add(modPath)
+                self._modPathsSeen.add(modPath)
 
-            debug.logger & debug.FLAG_BLD and debug.logger('loadModule: evaluating %s' % modPath)
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'loadModule: evaluating %s' % modPath)
 
-            g = {'mibBuilder': self, 'userCtx': userCtx}
+            g = {'mibBuilder': self,
+                 'userCtx': userCtx}
 
             try:
                 exec(codeObj, g)
 
             except Exception:
-                self.__modPathsSeen.remove(modPath)
+                self._modPathsSeen.remove(modPath)
                 raise error.MibLoadError(
-                    'MIB module \'%s\' load error: %s' % (modPath, traceback.format_exception(*sys.exc_info()))
-                )
+                    'MIB module "%s" load error: '
+                    '%s' % (modPath, traceback.format_exception(*sys.exc_info())))
 
-            self.__modSeen[modName] = modPath
+            self._modSeen[modName] = modPath
 
-            debug.logger & debug.FLAG_BLD and debug.logger('loadModule: loaded %s' % modPath)
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'loadModule: loaded %s' % modPath)
 
             break
 
-        if modName not in self.__modSeen:
+        if modName not in self._modSeen:
             raise error.MibNotFoundError(
-                'MIB file \"%s\" not found in search path (%s)' % (
-                    modName and modName + ".py[co]", ', '.join([str(x) for x in self.__mibSources]))
-            )
+                'MIB file "%s" not found in search path '
+                '(%s)' % (modName and modName + ".py[co]", ', '.join(
+                    [str(x) for x in self._mibSources])))
 
         return self
 
@@ -353,28 +403,36 @@ class MibBuilder(object):
         # Build a list of available modules
         if not modNames:
             modNames = {}
-            for mibSource in self.__mibSources:
+
+            for mibSource in self._mibSources:
                 for modName in mibSource.listdir():
                     modNames[modName] = None
+
             modNames = list(modNames)
 
         if not modNames:
             raise error.MibNotFoundError(
-                'No MIB module to load at %s' % (self,)
-            )
+                'No MIB module to load at %s' % (self,))
 
         for modName in modNames:
             try:
                 self.loadModule(modName, **userCtx)
 
             except error.MibNotFoundError:
-                if self.__mibCompiler:
-                    debug.logger & debug.FLAG_BLD and debug.logger('loadModules: calling MIB compiler for %s' % modName)
-                    status = self.__mibCompiler.compile(modName, genTexts=self.loadTexts)
-                    errs = '; '.join([hasattr(x, 'error') and str(x.error) or x for x in status.values() if
-                                      x in ('failed', 'missing')])
+                if self._mibCompiler:
+                    debug.logger & debug.FLAG_BLD and debug.logger(
+                        'loadModules: calling MIB compiler for %s' % modName)
+
+                    status = self._mibCompiler.compile(modName, genTexts=self.loadTexts)
+
+                    errs = '; '.join(
+                        hasattr(x, 'error') and str(x.error) or x
+                        for x in status.values()
+                        if x in ('failed', 'missing'))
+
                     if errs:
-                        raise error.MibNotFoundError('%s compilation error(s): %s' % (modName, errs))
+                        raise error.MibNotFoundError(
+                            '%s compilation error(s): %s' % (modName, errs))
 
                     # compilation succeeded, MIB might load now
                     self.loadModule(modName, **userCtx)
@@ -383,84 +441,103 @@ class MibBuilder(object):
 
     def unloadModules(self, *modNames):
         if not modNames:
-            modNames = list(self.mibSymbols.keys())
+            modNames = list(self.mibSymbols)
+
         for modName in modNames:
             if modName not in self.mibSymbols:
                 raise error.MibNotFoundError(
-                    'No module %s at %s' % (modName, self)
-                )
+                    'No module %s at %s' % (modName, self))
+
             self.unexportSymbols(modName)
-            self.__modPathsSeen.remove(self.__modSeen[modName])
-            del self.__modSeen[modName]
 
-            debug.logger & debug.FLAG_BLD and debug.logger('unloadModules: %s' % modName)
+            self._modPathsSeen.remove(self._modSeen[modName])
+
+            del self._modSeen[modName]
+
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'unloadModules: %s' % modName)
 
         return self
 
     def importSymbols(self, modName, *symNames, **userCtx):
         if not modName:
             raise error.SmiError(
-                'importSymbols: empty MIB module name'
-            )
-        r = ()
+                'importSymbols: empty MIB module name')
+
+        symbols = []
+
         for symName in symNames:
             if modName not in self.mibSymbols:
                 self.loadModules(modName, **userCtx)
+
             if modName not in self.mibSymbols:
                 raise error.MibNotFoundError(
-                    'No module %s loaded at %s' % (modName, self)
-                )
+                    'No module %s loaded at %s' % (modName, self))
+
             if symName not in self.mibSymbols[modName]:
                 raise error.SmiError(
-                    'No symbol %s::%s at %s' % (modName, symName, self)
-                )
-            r = r + (self.mibSymbols[modName][symName],)
-        return r
+                    'No symbol %s::%s at %s' % (modName, symName, self))
+
+            symbols.append(self.mibSymbols[modName][symName])
+
+        return symbols
 
     def exportSymbols(self, modName, *anonymousSyms, **namedSyms):
         if modName not in self.mibSymbols:
             self.mibSymbols[modName] = {}
+
         mibSymbols = self.mibSymbols[modName]
 
         for symObj in anonymousSyms:
             debug.logger & debug.FLAG_BLD and debug.logger(
-                'exportSymbols: anonymous symbol %s::__pysnmp_%ld' % (modName, self._autoName))
+                'exportSymbols: anonymous symbol %s::'
+                '__pysnmp_%ld' % (modName, self._autoName))
+
             mibSymbols['__pysnmp_%ld' % self._autoName] = symObj
+
             self._autoName += 1
+
         for symName, symObj in namedSyms.items():
             if symName in mibSymbols:
                 raise error.SmiError(
-                    'Symbol %s already exported at %s' % (symName, modName)
-                )
+                    'Symbol %s already exported at %s' % (symName, modName))
+
+            if (symName != self.moduleID and
+                    not isinstance(symObj, classTypes)):
 
-            if symName != self.moduleID and \
-                    not isinstance(symObj, classTypes):
                 label = symObj.getLabel()
+
                 if label:
                     symName = label
+
                 else:
                     symObj.setLabel(symName)
 
             mibSymbols[symName] = symObj
 
-            debug.logger & debug.FLAG_BLD and debug.logger('exportSymbols: symbol %s::%s' % (modName, symName))
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'exportSymbols: symbol %s::%s' % (modName, symName))
 
         self.lastBuildId += 1
 
     def unexportSymbols(self, modName, *symNames):
         if modName not in self.mibSymbols:
             raise error.SmiError('No module %s at %s' % (modName, self))
+
         mibSymbols = self.mibSymbols[modName]
+
         if not symNames:
             symNames = list(mibSymbols.keys())
+
         for symName in symNames:
             if symName not in mibSymbols:
                 raise error.SmiError(
-                    'No symbol %s::%s at %s' % (modName, symName, self)
-                )
+                    'No symbol %s::%s at %s' % (modName, symName, self))
+
             del mibSymbols[symName]
 
-            debug.logger & debug.FLAG_BLD and debug.logger('unexportSymbols: symbol %s::%s' % (modName, symName))
+            debug.logger & debug.FLAG_BLD and debug.logger(
+                'unexportSymbols: symbol %s::%s' % (modName, symName))
 
         if not self.mibSymbols[modName]:
             del self.mibSymbols[modName]
diff --git a/pysnmp/smi/compiler.py b/pysnmp/smi/compiler.py
index 231685f8..6c4d3d11 100644
--- a/pysnmp/smi/compiler.py
+++ b/pysnmp/smi/compiler.py
@@ -33,9 +33,11 @@ except ImportError as exc:
 
 
     def addMibCompilerDecorator(errorMsg):
+
         def addMibCompiler(mibBuilder, **kwargs):
             if not kwargs.get('ifAvailable'):
-                raise error.SmiError('MIB compiler not available: %s' % errorMsg)
+                raise error.SmiError(
+                    'MIB compiler not available: %s' % errorMsg)
 
         return addMibCompiler
 
@@ -48,18 +50,25 @@ else:
         if kwargs.get('ifNotAdded') and mibBuilder.getMibCompiler():
             return
 
-        compiler = MibCompiler(parserFactory(**smiV1Relaxed)(),
-                               PySnmpCodeGen(),
-                               PyFileWriter(kwargs.get('destination') or DEFAULT_DEST))
+        compiler = MibCompiler(
+            parserFactory(**smiV1Relaxed)(),
+            PySnmpCodeGen(),
+            PyFileWriter(kwargs.get('destination') or DEFAULT_DEST))
+
+        compiler.addSources(
+            *getReadersFromUrls(*kwargs.get('sources') or DEFAULT_SOURCES))
+
+        compiler.addSearchers(
+            StubSearcher(*baseMibs))
 
-        compiler.addSources(*getReadersFromUrls(*kwargs.get('sources') or DEFAULT_SOURCES))
+        compiler.addSearchers(
+            *[PyPackageSearcher(x.fullPath()) for x in mibBuilder.getMibSources()])
 
-        compiler.addSearchers(StubSearcher(*baseMibs))
-        compiler.addSearchers(*[PyPackageSearcher(x.fullPath()) for x in mibBuilder.getMibSources()])
-        compiler.addBorrowers(*[PyFileBorrower(x, genTexts=mibBuilder.loadTexts) for x in
-                                getReadersFromUrls(*kwargs.get('borrowers') or DEFAULT_BORROWERS,
-                                                   lowcaseMatching=False)])
+        compiler.addBorrowers(
+            *[PyFileBorrower(x, genTexts=mibBuilder.loadTexts)
+              for x in getReadersFromUrls(
+                    *kwargs.get('borrowers') or DEFAULT_BORROWERS,
+                    lowcaseMatching=False)])
 
         mibBuilder.setMibCompiler(
-            compiler, kwargs.get('destination') or DEFAULT_DEST
-        )
+            compiler, kwargs.get('destination') or DEFAULT_DEST)
diff --git a/pysnmp/smi/error.py b/pysnmp/smi/error.py
index 87909b1e..1322a2c5 100644
--- a/pysnmp/smi/error.py
+++ b/pysnmp/smi/error.py
@@ -23,25 +23,25 @@ class MibNotFoundError(MibLoadError):
 
 class MibOperationError(SmiError):
     def __init__(self, **kwargs):
-        self.__outArgs = kwargs
+        self._outArgs = kwargs
 
     def __str__(self):
-        return '%s(%s)' % (self.__class__.__name__, self.__outArgs)
+        return '%s(%s)' % (self.__class__.__name__, self._outArgs)
 
     def __getitem__(self, key):
-        return self.__outArgs[key]
+        return self._outArgs[key]
 
     def __contains__(self, key):
-        return key in self.__outArgs
+        return key in self._outArgs
 
     def get(self, key, defVal=None):
-        return self.__outArgs.get(key, defVal)
+        return self._outArgs.get(key, defVal)
 
     def keys(self):
-        return self.__outArgs.keys()
+        return self._outArgs.keys()
 
     def update(self, d):
-        self.__outArgs.update(d)
+        self._outArgs.update(d)
 
 
 # Aligned with SNMPv2 PDU error-status values
diff --git a/pysnmp/smi/indices.py b/pysnmp/smi/indices.py
index 677ac97c..f55f7e6a 100644
--- a/pysnmp/smi/indices.py
+++ b/pysnmp/smi/indices.py
@@ -11,45 +11,50 @@ class OrderedDict(dict):
     """Ordered dictionary used for indices"""
 
     def __init__(self, *args, **kwargs):
-        self.__keys = []
-        self.__dirty = True
         super(OrderedDict, self).__init__()
+
+        self._keys = []
+        self._dirty = True
+        self._keysLens = []
+
         if args:
             self.update(*args)
+
         if kwargs:
             self.update(**kwargs)
 
     def __setitem__(self, key, value):
         super(OrderedDict, self).__setitem__(key, value)
-        if key not in self.__keys:
-            self.__keys.append(key)
-            self.__dirty = True
+        if key not in self._keys:
+            self._keys.append(key)
+            self._dirty = True
 
     def __delitem__(self, key):
         super(OrderedDict, self).__delitem__(key)
-        if key in self.__keys:
-            self.__keys.remove(key)
-            self.__dirty = True
+        if key in self._keys:
+            self._keys.remove(key)
+            self._dirty = True
 
     def clear(self):
         super(OrderedDict, self).clear()
-        self.__keys = []
-        self.__dirty = True
+        self._keys = []
+        self._dirty = True
 
     def keys(self):
-        if self.__dirty:
-            self.__order()
-        return list(self.__keys)
+        if self._dirty:
+            self._order()
+        return list(self._keys)
 
     def values(self):
-        if self.__dirty:
-            self.__order()
-        return [self[k] for k in self.__keys]
+        if self._dirty:
+            self._order()
+        return [self[k] for k in self._keys]
 
     def items(self):
-        if self.__dirty:
-            self.__order()
-        return [(k, self[k]) for k in self.__keys]
+        if self._dirty:
+            self._order()
+
+        return [(k, self[k]) for k in self._keys]
 
     def update(self, *args, **kwargs):
         if args:
@@ -57,6 +62,7 @@ class OrderedDict(dict):
             if hasattr(iterable, 'keys'):
                 for k in iterable:
                     self[k] = iterable[k]
+
             else:
                 for k, v in iterable:
                     self[k] = v
@@ -68,16 +74,19 @@ class OrderedDict(dict):
     def sortingFun(self, keys):
         keys.sort()
 
-    def __order(self):
-        self.sortingFun(self.__keys)
-        self.__keysLens = sorted(set(len(k) for k in self.__keys), reverse=True)
-        self.__dirty = False
+    def _order(self):
+        self.sortingFun(self._keys)
+
+        self._keysLens = sorted(
+            set(len(k) for k in self._keys), reverse=True)
+
+        self._dirty = False
 
     def nextKey(self, key):
-        if self.__dirty:
-            self.__order()
+        if self._dirty:
+            self._order()
 
-        keys = self.__keys
+        keys = self._keys
 
         if key in keys:
             nextIdx = keys.index(key) + 1
@@ -92,30 +101,35 @@ class OrderedDict(dict):
             raise KeyError(key)
 
     def getKeysLens(self):
-        if self.__dirty:
-            self.__order()
-        return self.__keysLens
+        if self._dirty:
+            self._order()
+
+        return self._keysLens
 
 
 class OidOrderedDict(OrderedDict):
     """OID-ordered dictionary used for indices"""
 
     def __init__(self, *args, **kwargs):
-        self.__keysCache = {}
         OrderedDict.__init__(self, *args, **kwargs)
 
+        self._keysCache = {}
+
     def __setitem__(self, key, value):
         OrderedDict.__setitem__(self, key, value)
-        if key not in self.__keysCache:
+
+        if key not in self._keysCache:
             if isinstance(key, tuple):
-                self.__keysCache[key] = key
+                self._keysCache[key] = key
+
             else:
-                self.__keysCache[key] = [int(x) for x in key.split('.') if x]
+                self._keysCache[key] = [int(x) for x in key.split('.') if x]
 
     def __delitem__(self, key):
         OrderedDict.__delitem__(self, key)
-        if key in self.__keysCache:
-            del self.__keysCache[key]
+
+        if key in self._keysCache:
+            del self._keysCache[key]
 
     def sortingFun(self, keys):
-        keys.sort(key=lambda k, d=self.__keysCache: d[k])
+        keys.sort(key=lambda k, d=self._keysCache: d[k])
diff --git a/pysnmp/smi/instrum.py b/pysnmp/smi/instrum.py
index aec25adc..342eeb6b 100644
--- a/pysnmp/smi/instrum.py
+++ b/pysnmp/smi/instrum.py
@@ -38,21 +38,21 @@ class MibInstrumController(AbstractMibInstrumController):
     STATE_WRITE_CLEANUP = 'writeCleanup'
     STATE_WRITE_UNDO = 'writeUndo'
 
-    fsmReadVar = {
+    FSM_READ_VAR = {
         # (state, status) -> newState
         (STATE_START, STATUS_OK): STATE_READ_TEST,
         (STATE_READ_TEST, STATUS_OK): STATE_READ_GET,
         (STATE_READ_GET, STATUS_OK): STATE_STOP,
         (STATE_ANY, STATUS_ERROR): STATE_STOP
     }
-    fsmReadNextVar = {
+    FSM_READ_NEXT_VAR = {
         # (state, status) -> newState
         (STATE_START, STATUS_OK): STATE_READ_TEST_NEXT,
         (STATE_READ_TEST_NEXT, STATUS_OK): STATE_READ_GET_NEXT,
         (STATE_READ_GET_NEXT, STATUS_OK): STATE_STOP,
         (STATE_ANY, STATUS_ERROR): STATE_STOP
     }
-    fsmWriteVar = {
+    FSM_WRITE_VAR = {
         # (state, status) -> newState
         (STATE_START, STATUS_OK): STATE_WRITE_TEST,
         (STATE_WRITE_TEST, STATUS_OK): STATE_WRITE_COMMIT,
@@ -79,7 +79,7 @@ class MibInstrumController(AbstractMibInstrumController):
     def getMibBuilder(self):
         return self.mibBuilder
 
-    def __indexMib(self):
+    def _indexMib(self):
         """Rebuild a tree from MIB objects found at currently loaded modules.
 
         If currently existing tree is out of date, walk over all Managed Objects
@@ -108,7 +108,8 @@ class MibInstrumController(AbstractMibInstrumController):
         if self.lastBuildId == self.mibBuilder.lastBuildId:
             return
 
-        (MibScalarInstance, MibScalar, MibTableColumn, MibTableRow,
+        (MibScalarInstance, MibScalar,
+         MibTableColumn, MibTableRow,
          MibTable) = self.mibBuilder.importSymbols(
             'SNMPv2-SMI', 'MibScalarInstance', 'MibScalar',
             'MibTableColumn', 'MibTableRow', 'MibTable'
@@ -128,26 +129,36 @@ class MibInstrumController(AbstractMibInstrumController):
         mibSymbols.sort(key=lambda x: x[0], reverse=True)
 
         for modName, mibMod in mibSymbols:
+
             for symObj in mibMod.values():
+
                 if isinstance(symObj, MibTable):
                     tables[symObj.name] = symObj
+
                 elif isinstance(symObj, MibTableRow):
                     rows[symObj.name] = symObj
+
                 elif isinstance(symObj, MibTableColumn):
                     cols[symObj.name] = symObj
+
                 elif isinstance(symObj, MibScalarInstance):
                     instances[symObj.name] = symObj
+
                 elif isinstance(symObj, MibScalar):
                     scalars[symObj.name] = symObj
 
         # Detach items from each other
         for symName, parentName in self.lastBuildSyms.items():
+
             if parentName in scalars:
                 scalars[parentName].unregisterSubtrees(symName)
+
             elif parentName in cols:
                 cols[parentName].unregisterSubtrees(symName)
+
             elif parentName in rows:
                 rows[parentName].unregisterSubtrees(symName)
+
             else:
                 mibTree.unregisterSubtrees(symName)
 
@@ -157,23 +168,29 @@ class MibInstrumController(AbstractMibInstrumController):
         for inst in instances.values():
             if inst.typeName in scalars:
                 scalars[inst.typeName].registerSubtrees(inst)
+
             elif inst.typeName in cols:
                 cols[inst.typeName].registerSubtrees(inst)
+
             else:
                 raise error.SmiError(
-                    'Orphan MIB scalar instance %r at %r' % (inst, self)
-                )
+                    'Orphan MIB scalar instance %r at '
+                    '%r' % (inst, self))
+
             lastBuildSyms[inst.name] = inst.typeName
 
         # Attach Table Columns to Table Rows
         for col in cols.values():
             rowName = col.name[:-1]  # XXX
+
             if rowName in rows:
                 rows[rowName].registerSubtrees(col)
+
             else:
                 raise error.SmiError(
-                    'Orphan MIB table column %r at %r' % (col, self)
-                )
+                    'Orphan MIB table column %r at '
+                    '%r' % (col, self))
+
             lastBuildSyms[col.name] = rowName
 
         # Attach Table Rows to MIB tree
@@ -195,7 +212,7 @@ class MibInstrumController(AbstractMibInstrumController):
 
         self.lastBuildId = self.mibBuilder.lastBuildId
 
-        debug.logger & debug.FLAG_INS and debug.logger('__indexMib: rebuilt')
+        debug.logger & debug.FLAG_INS and debug.logger('_indexMib: rebuilt')
 
     def flipFlopFsm(self, fsmTable, *varBinds, **context):
         """Read, modify, create or remove Managed Objects Instances.
@@ -250,12 +267,12 @@ class MibInstrumController(AbstractMibInstrumController):
             if err:
                 # Move other errors into the errors sequence
                 errors = context['errors']
+
                 errors.append(
                     {'error': err,
                      'idx': idx,
                      'varbind': varBind,
-                     'state': context['state']}
-                )
+                     'state': context['state']})
 
                 context['status'] = self.STATUS_ERROR
 
@@ -271,8 +288,8 @@ class MibInstrumController(AbstractMibInstrumController):
             count[0] += 1
 
             debug.logger & debug.FLAG_INS and debug.logger(
-                '_cbFun: var-bind %d, processed %d, expected %d' % (
-                idx, count[0], len(varBinds)))
+                '_cbFun: var-bind %d, processed %d, expected '
+                '%d' % (idx, count[0], len(varBinds)))
 
             if count[0] < len(varBinds):
                 return
@@ -282,7 +299,8 @@ class MibInstrumController(AbstractMibInstrumController):
 
             self.flipFlopFsm(fsmTable, *varBinds, **dict(context, cbFun=cbFun))
 
-        debug.logger & debug.FLAG_INS and debug.logger('flipFlopFsm: input var-binds %r' % (varBinds,))
+        debug.logger & debug.FLAG_INS and debug.logger(
+            'flipFlopFsm: input var-binds %r' % (varBinds,))
 
         mibTree, = self.mibBuilder.importSymbols('SNMPv2-SMI', 'iso')
 
@@ -299,7 +317,7 @@ class MibInstrumController(AbstractMibInstrumController):
             errors = []
             _varBinds = list(varBinds)
 
-            self.__indexMib()
+            self._indexMib()
 
         debug.logger & debug.FLAG_INS and debug.logger(
             'flipFlopFsm: current state %s, status %s' % (state, status))
@@ -312,10 +330,12 @@ class MibInstrumController(AbstractMibInstrumController):
                 newState = fsmTable[(self.STATE_ANY, status)]
 
             except KeyError:
-                raise error.SmiError('Unresolved FSM state %s, %s' % (state, status))
+                raise error.SmiError(
+                    'Unresolved FSM state %s, %s' % (state, status))
 
         debug.logger & debug.FLAG_INS and debug.logger(
-            'flipFlopFsm: state %s status %s -> transitioned into state %s' % (state, status, newState))
+            'flipFlopFsm: state %s status %s -> transitioned into state '
+            '%s' % (state, status, newState))
 
         state = newState
 
@@ -324,8 +344,10 @@ class MibInstrumController(AbstractMibInstrumController):
             context.pop('status', None)
             context.pop('instances', None)
             context.pop('varBinds', None)
+
             if cbFun:
                 cbFun(_varBinds, **context)
+
             return
 
         # the case of no var-binds
@@ -336,16 +358,15 @@ class MibInstrumController(AbstractMibInstrumController):
         actionFun = getattr(mibTree, state, None)
         if not actionFun:
             raise error.SmiError(
-                'Unsupported state handler %s at %s' % (state, self)
-            )
+                'Unsupported state handler %s at '
+                '%s' % (state, self))
 
         for idx, varBind in enumerate(varBinds):
-            actionFun(varBind,
-                      **dict(context, cbFun=_cbFun,
-                             state=state, status=status,
-                             idx=idx, total=len(varBinds),
-                             instances=instances, errors=errors,
-                             varBinds=_varBinds, nextName=None))
+            actionFun(
+                varBind,
+                **dict(context, cbFun=_cbFun, state=state, status=status,
+                       idx=idx, total=len(varBinds), instances=instances,
+                       errors=errors, varBinds=_varBinds, nextName=None))
 
             debug.logger & debug.FLAG_INS and debug.logger(
                 'flipFlopFsm: func %s initiated for %r' % (actionFun, varBind))
@@ -354,9 +375,10 @@ class MibInstrumController(AbstractMibInstrumController):
     def _defaultErrorHandler(varBinds, **context):
         """Raise exception on any error if user callback is missing"""
         errors = context.get('errors')
+
         if errors:
-            error = errors[-1]
-            raise error['error']
+            err = errors[-1]
+            raise err['error']
 
     def readMibObjects(self, *varBinds, **context):
         """Read Managed Objects Instances.
@@ -410,7 +432,7 @@ class MibInstrumController(AbstractMibInstrumController):
         if 'cbFun' not in context:
             context['cbFun'] = self._defaultErrorHandler
 
-        self.flipFlopFsm(self.fsmReadVar, *varBinds, **context)
+        self.flipFlopFsm(self.FSM_READ_VAR, *varBinds, **context)
 
     def readNextMibObjects(self, *varBinds, **context):
         """Read Managed Objects Instances next to the given ones.
@@ -470,7 +492,7 @@ class MibInstrumController(AbstractMibInstrumController):
         if 'cbFun' not in context:
             context['cbFun'] = self._defaultErrorHandler
 
-        self.flipFlopFsm(self.fsmReadNextVar, *varBinds, **context)
+        self.flipFlopFsm(self.FSM_READ_NEXT_VAR, *varBinds, **context)
 
     def writeMibObjects(self, *varBinds, **context):
         """Create, destroy or modify Managed Objects Instances.
@@ -539,4 +561,4 @@ class MibInstrumController(AbstractMibInstrumController):
         if 'cbFun' not in context:
             context['cbFun'] = self._defaultErrorHandler
 
-        self.flipFlopFsm(self.fsmWriteVar, *varBinds, **context)
+        self.flipFlopFsm(self.FSM_WRITE_VAR, *varBinds, **context)
diff --git a/pysnmp/smi/rfc1902.py b/pysnmp/smi/rfc1902.py
index 9a3d4507..40249a1e 100644
--- a/pysnmp/smi/rfc1902.py
+++ b/pysnmp/smi/rfc1902.py
@@ -4,9 +4,6 @@
 # Copyright (c) 2005-2019, Ilya Etingof <etingof@gmail.com>
 # License: http://snmplabs.com/pysnmp/license.html
 #
-from pyasn1.error import PyAsn1Error
-from pyasn1.type.base import AbstractSimpleAsn1Item
-
 from pysnmp import debug
 from pysnmp.proto import rfc1902
 from pysnmp.proto import rfc1905
@@ -15,6 +12,9 @@ from pysnmp.smi.builder import ZipMibSource
 from pysnmp.smi.compiler import addMibCompiler
 from pysnmp.smi.error import SmiError
 
+from pyasn1.error import PyAsn1Error
+from pyasn1.type.base import AbstractSimpleAsn1Item
+
 __all__ = ['ObjectIdentity', 'ObjectType', 'NotificationType']
 
 
@@ -78,19 +78,22 @@ class ObjectIdentity(object):
     ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0)
     >>> ObjectIdentity('IP-MIB', 'ipAdEntAddr', '127.0.0.1', 123)
     ObjectIdentity('IP-MIB', 'ipAdEntAddr', '127.0.0.1', 123)
-
     """
     ST_DIRTY, ST_CLEAN = 1, 2
 
     def __init__(self, *args, **kwargs):
-        self.__args = args
-        self.__kwargs = kwargs
-        self.__mibSourcesToAdd = self.__modNamesToLoad = None
-        self.__asn1SourcesToAdd = self.__asn1SourcesOptions = None
-        self.__state = self.ST_DIRTY
-        self.__indices = self.__oid = self.__label = ()
-        self.__modName = self.__symName = ''
-        self.__mibNode = None
+        self._args = args
+        self._kwargs = kwargs
+        self._mibSourcesToAdd = None
+        self._modNamesToLoad = None
+        self._asn1SourcesToAdd = None
+        self._asn1SourcesOptions = None
+        self._state = self.ST_DIRTY
+        self._indices = ()
+        self._oid = ()
+        self._label = ()
+        self._modName = self._symName = ''
+        self._mibNode = None
 
     def getMibSymbol(self):
         """Returns MIB variable symbolic identification.
@@ -116,12 +119,13 @@ class ObjectIdentity(object):
         >>> objectIdentity.getMibSymbol()
         ('SNMPv2-MIB', 'sysDescr', (0,))
         >>>
-
         """
-        if self.__state & self.ST_CLEAN:
-            return self.__modName, self.__symName, self.__indices
+        if self._state & self.ST_CLEAN:
+            return self._modName, self._symName, self._indices
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def getOid(self):
         """Returns OID identifying MIB variable.
@@ -143,12 +147,13 @@ class ObjectIdentity(object):
         >>> objectIdentity.getOid()
         ObjectName('1.3.6.1.2.1.1.1.0')
         >>>
-
         """
-        if self.__state & self.ST_CLEAN:
-            return self.__oid
+        if self._state & self.ST_CLEAN:
+            return self._oid
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def getLabel(self):
         """Returns symbolic path to this MIB variable.
@@ -179,21 +184,24 @@ class ObjectIdentity(object):
         >>> objectIdentity.getOid()
         ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'system', 'sysDescr')
         >>>
-
         """
-        if self.__state & self.ST_CLEAN:
-            return self.__label
+        if self._state & self.ST_CLEAN:
+            return self._label
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def getMibNode(self):
-        if self.__state & self.ST_CLEAN:
-            return self.__mibNode
+        if self._state & self.ST_CLEAN:
+            return self._mibNode
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def isFullyResolved(self):
-        return self.__state & self.ST_CLEAN
+        return self._state & self.ST_CLEAN
 
     #
     # A gateway to MIBs manipulation routines
@@ -227,16 +235,19 @@ class ObjectIdentity(object):
         >>> ObjectIdentity('SNMPv2-MIB', 'sysDescr').addAsn1Source('http://mibs.snmplabs.com/asn1/@mib@')
         ObjectIdentity('SNMPv2-MIB', 'sysDescr')
         >>>
-
         """
-        if self.__asn1SourcesToAdd is None:
-            self.__asn1SourcesToAdd = asn1Sources
+        if self._asn1SourcesToAdd is None:
+            self._asn1SourcesToAdd = asn1Sources
+
         else:
-            self.__asn1SourcesToAdd += asn1Sources
-        if self.__asn1SourcesOptions:
-            self.__asn1SourcesOptions.update(kwargs)
+            self._asn1SourcesToAdd += asn1Sources
+
+        if self._asn1SourcesOptions:
+            self._asn1SourcesOptions.update(kwargs)
+
         else:
-            self.__asn1SourcesOptions = kwargs
+            self._asn1SourcesOptions = kwargs
+
         return self
 
     def addMibSource(self, *mibSources):
@@ -266,12 +277,13 @@ class ObjectIdentity(object):
         >>> ObjectIdentity('SNMPv2-MIB', 'sysDescr').addMibSource('/opt/pysnmp/mibs', 'pysnmp_mibs')
         ObjectIdentity('SNMPv2-MIB', 'sysDescr')
         >>>
-
         """
-        if self.__mibSourcesToAdd is None:
-            self.__mibSourcesToAdd = mibSources
+        if self._mibSourcesToAdd is None:
+            self._mibSourcesToAdd = mibSources
+
         else:
-            self.__mibSourcesToAdd += mibSources
+            self._mibSourcesToAdd += mibSources
+
         return self
 
     # provides deferred MIBs load
@@ -294,12 +306,13 @@ class ObjectIdentity(object):
         >>> ObjectIdentity('SNMPv2-MIB', 'sysDescr').loadMibs('IF-MIB', 'TCP-MIB')
         ObjectIdentity('SNMPv2-MIB', 'sysDescr')
         >>>
-
         """
-        if self.__modNamesToLoad is None:
-            self.__modNamesToLoad = modNames
+        if self._modNamesToLoad is None:
+            self._modNamesToLoad = modNames
+
         else:
-            self.__modNamesToLoad += modNames
+            self._modNamesToLoad += modNames
+
         return self
 
     # this would eventually be called by an entity which posses a
@@ -344,298 +357,382 @@ class ObjectIdentity(object):
         >>> objectIdentity.resolveWithMib(mibViewController)
         ObjectIdentity('SNMPv2-MIB', 'sysDescr')
         >>>
-
         """
-        if self.__mibSourcesToAdd is not None:
-            debug.logger & debug.FLAG_MIB and debug.logger('adding MIB sources %s' % ', '.join(self.__mibSourcesToAdd))
+        if self._mibSourcesToAdd is not None:
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'adding MIB sources %s' % ', '.join(self._mibSourcesToAdd))
+
             mibViewController.mibBuilder.addMibSources(
-                *[ZipMibSource(x) for x in self.__mibSourcesToAdd]
-            )
-            self.__mibSourcesToAdd = None
+                *[ZipMibSource(x) for x in self._mibSourcesToAdd])
+
+            self._mibSourcesToAdd = None
+
+        if self._asn1SourcesToAdd is None:
+            addMibCompiler(
+                mibViewController.mibBuilder,
+                ifAvailable=True, ifNotAdded=True)
 
-        if self.__asn1SourcesToAdd is None:
-            addMibCompiler(mibViewController.mibBuilder,
-                           ifAvailable=True, ifNotAdded=True)
         else:
             debug.logger & debug.FLAG_MIB and debug.logger(
-                'adding MIB compiler with source paths %s' % ', '.join(self.__asn1SourcesToAdd))
+                'adding MIB compiler with source paths '
+                '%s' % ', '.join(self._asn1SourcesToAdd))
+
             addMibCompiler(
                 mibViewController.mibBuilder,
-                sources=self.__asn1SourcesToAdd,
-                searchers=self.__asn1SourcesOptions.get('searchers'),
-                borrowers=self.__asn1SourcesOptions.get('borrowers'),
-                destination=self.__asn1SourcesOptions.get('destination'),
-                ifAvailable=self.__asn1SourcesOptions.get('ifAvailable'),
-                ifNotAdded=self.__asn1SourcesOptions.get('ifNotAdded')
+                sources=self._asn1SourcesToAdd,
+                searchers=self._asn1SourcesOptions.get('searchers'),
+                borrowers=self._asn1SourcesOptions.get('borrowers'),
+                destination=self._asn1SourcesOptions.get('destination'),
+                ifAvailable=self._asn1SourcesOptions.get('ifAvailable'),
+                ifNotAdded=self._asn1SourcesOptions.get('ifNotAdded')
             )
-            self.__asn1SourcesToAdd = self.__asn1SourcesOptions = None
 
-        if self.__modNamesToLoad is not None:
-            debug.logger & debug.FLAG_MIB and debug.logger('loading MIB modules %s' % ', '.join(self.__modNamesToLoad))
-            mibViewController.mibBuilder.loadModules(*self.__modNamesToLoad)
-            self.__modNamesToLoad = None
+            self._asn1SourcesToAdd = self._asn1SourcesOptions = None
+
+        if self._modNamesToLoad is not None:
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'loading MIB modules %s' % ', '.join(self._modNamesToLoad))
+
+            mibViewController.mibBuilder.loadModules(*self._modNamesToLoad)
+
+            self._modNamesToLoad = None
 
-        if self.__state & self.ST_CLEAN:
+        if self._state & self.ST_CLEAN:
             return self
 
-        MibScalar, MibTableColumn = mibViewController.mibBuilder.importSymbols('SNMPv2-SMI', 'MibScalar',
-                                                                               'MibTableColumn')
+        MibScalar, MibTableColumn = mibViewController.mibBuilder.importSymbols(
+            'SNMPv2-SMI', 'MibScalar', 'MibTableColumn')
 
-        self.__indices = ()
+        self._indices = ()
 
-        if isinstance(self.__args[0], ObjectIdentity):
-            self.__args[0].resolveWithMib(mibViewController)
+        if isinstance(self._args[0], ObjectIdentity):
+            self._args[0].resolveWithMib(mibViewController)
+
+        if len(self._args) == 1:  # OID or label or MIB module
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'resolving %s as OID or label' % self._args)
 
-        if len(self.__args) == 1:  # OID or label or MIB module
-            debug.logger & debug.FLAG_MIB and debug.logger('resolving %s as OID or label' % self.__args)
             try:
                 # pyasn1 ObjectIdentifier or sequence of ints or string OID
-                self.__oid = rfc1902.ObjectName(self.__args[0])  # OID
+                self._oid = rfc1902.ObjectName(self._args[0])  # OID
+
             except PyAsn1Error:
                 # sequence of sub-OIDs and labels
-                if isinstance(self.__args[0], (list, tuple)):
+                if isinstance(self._args[0], (list, tuple)):
                     prefix, label, suffix = mibViewController.getNodeName(
-                        self.__args[0]
-                    )
+                        self._args[0])
+
                 # string label
-                elif '.' in self.__args[0]:
+                elif '.' in self._args[0]:
                     prefix, label, suffix = mibViewController.getNodeNameByOid(
-                        tuple(self.__args[0].split('.'))
-                    )
+                        tuple(self._args[0].split('.')))
+
                 # MIB module name
                 else:
-                    modName = self.__args[0]
+                    modName = self._args[0]
+
                     mibViewController.mibBuilder.loadModules(modName)
-                    if self.__kwargs.get('last'):
-                        prefix, label, suffix = mibViewController.getLastNodeName(modName)
+
+                    if self._kwargs.get('last'):
+                        (prefix, label,
+                         suffix) = mibViewController.getLastNodeName(modName)
+
                     else:
-                        prefix, label, suffix = mibViewController.getFirstNodeName(modName)
+                        (prefix, label,
+                         suffix) = mibViewController.getFirstNodeName(modName)
 
                 if suffix:
                     try:
-                        suffix = tuple([int(x) for x in suffix])
+                        suffix = tuple(int(x) for x in suffix)
+
                     except ValueError:
-                        raise SmiError('Unknown object name component %r' % (suffix,))
-                self.__oid = rfc1902.ObjectName(prefix + suffix)
+                        raise SmiError(
+                            'Unknown object name component %r' % (suffix,))
+
+                self._oid = rfc1902.ObjectName(prefix + suffix)
+
             else:
                 prefix, label, suffix = mibViewController.getNodeNameByOid(
-                    self.__oid
-                )
+                    self._oid)
 
             debug.logger & debug.FLAG_MIB and debug.logger(
-                'resolved %r into prefix %r and suffix %r' % (self.__args, prefix, suffix))
+                'resolved %r into prefix %r and suffix '
+                '%r' % (self._args, prefix, suffix))
 
             modName, symName, _ = mibViewController.getNodeLocation(prefix)
 
-            self.__modName = modName
-            self.__symName = symName
+            self._modName = modName
+            self._symName = symName
 
-            self.__label = label
+            self._label = label
 
             mibNode, = mibViewController.mibBuilder.importSymbols(
-                modName, symName
-            )
+                modName, symName)
 
-            self.__mibNode = mibNode
+            self._mibNode = mibNode
 
-            debug.logger & debug.FLAG_MIB and debug.logger('resolved prefix %r into MIB node %r' % (prefix, mibNode))
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'resolved prefix %r into MIB node %r' % (prefix, mibNode))
 
             if isinstance(mibNode, MibTableColumn):  # table column
                 if suffix:
                     rowModName, rowSymName, _ = mibViewController.getNodeLocation(
                         mibNode.name[:-1]
                     )
+
                     rowNode, = mibViewController.mibBuilder.importSymbols(
                         rowModName, rowSymName
                     )
-                    self.__indices = rowNode.getIndicesFromInstId(suffix)
+
+                    self._indices = rowNode.getIndicesFromInstId(suffix)
+
             elif isinstance(mibNode, MibScalar):  # scalar
                 if suffix:
-                    self.__indices = (rfc1902.ObjectName(suffix),)
+                    self._indices = (rfc1902.ObjectName(suffix),)
+
             else:
                 if suffix:
-                    self.__indices = (rfc1902.ObjectName(suffix),)
-            self.__state |= self.ST_CLEAN
+                    self._indices = (rfc1902.ObjectName(suffix),)
+
+            self._state |= self.ST_CLEAN
 
-            debug.logger & debug.FLAG_MIB and debug.logger('resolved indices are %r' % (self.__indices,))
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'resolved indices are %r' % (self._indices,))
 
             return self
-        elif len(self.__args) > 1:  # MIB, symbol[, index, index ...]
+
+        elif len(self._args) > 1:  # MIB, symbol[, index, index ...]
             # MIB, symbol, index, index
-            if self.__args[0] and self.__args[1]:
-                self.__modName = self.__args[0]
-                self.__symName = self.__args[1]
+            if self._args[0] and self._args[1]:
+                self._modName = self._args[0]
+                self._symName = self._args[1]
+
             # MIB, ''
-            elif self.__args[0]:
-                mibViewController.mibBuilder.loadModules(self.__args[0])
-                if self.__kwargs.get('last'):
-                    prefix, label, suffix = mibViewController.getLastNodeName(self.__args[0])
+            elif self._args[0]:
+                mibViewController.mibBuilder.loadModules(self._args[0])
+
+                if self._kwargs.get('last'):
+                    (prefix, label,
+                     suffix) = mibViewController.getLastNodeName(self._args[0])
+
                 else:
-                    prefix, label, suffix = mibViewController.getFirstNodeName(self.__args[0])
-                self.__modName, self.__symName, _ = mibViewController.getNodeLocation(prefix)
+                    (prefix, label,
+                     suffix) = mibViewController.getFirstNodeName(self._args[0])
+
+                (self._modName,
+                 self._symName, _) = mibViewController.getNodeLocation(prefix)
+
             # '', symbol, index, index
             else:
-                prefix, label, suffix = mibViewController.getNodeName(self.__args[1:])
-                self.__modName, self.__symName, _ = mibViewController.getNodeLocation(prefix)
+                (prefix, label,
+                 suffix) = mibViewController.getNodeName(self._args[1:])
+
+                (self._modName,
+                 self._symName, _) = mibViewController.getNodeLocation(prefix)
 
             mibNode, = mibViewController.mibBuilder.importSymbols(
-                self.__modName, self.__symName
-            )
+                self._modName, self._symName)
 
-            self.__mibNode = mibNode
+            self._mibNode = mibNode
 
-            self.__oid = rfc1902.ObjectName(mibNode.getName())
+            self._oid = rfc1902.ObjectName(mibNode.getName())
 
-            prefix, label, suffix = mibViewController.getNodeNameByOid(
-                self.__oid
-            )
-            self.__label = label
+            (prefix, label,
+             suffix) = mibViewController.getNodeNameByOid(
+                self._oid)
+
+            self._label = label
 
             debug.logger & debug.FLAG_MIB and debug.logger(
-                'resolved %r into prefix %r and suffix %r' % (self.__args, prefix, suffix))
+                'resolved %r into prefix %r and suffix '
+                '%r' % (self._args, prefix, suffix))
 
             if isinstance(mibNode, MibTableColumn):  # table
                 rowModName, rowSymName, _ = mibViewController.getNodeLocation(
-                    mibNode.name[:-1]
-                )
+                    mibNode.name[:-1])
+
                 rowNode, = mibViewController.mibBuilder.importSymbols(
-                    rowModName, rowSymName
-                )
-                if self.__args[2:]:
+                    rowModName, rowSymName)
+
+                if self._args[2:]:
                     try:
-                        instIds = rowNode.getInstIdFromIndices(*self.__args[2:])
-                        self.__oid += instIds
-                        self.__indices = rowNode.getIndicesFromInstId(instIds)
+                        instIds = rowNode.getInstIdFromIndices(*self._args[2:])
+                        self._oid += instIds
+                        self._indices = rowNode.getIndicesFromInstId(instIds)
+
                     except PyAsn1Error as exc:
-                        raise SmiError('Instance index %r to OID conversion failure at object %r: %s' % (
-                            self.__args[2:], mibNode.getLabel(), exc))
-            elif self.__args[2:]:  # any other kind of MIB node with indices
-                if self.__args[2:]:
+                        raise SmiError(
+                            'Instance index %r to OID conversion failure '
+                            'at object %r: '
+                            '%s' % (self._args[2:], mibNode.getLabel(), exc))
+
+            elif self._args[2:]:  # any other kind of MIB node with indices
+                if self._args[2:]:
                     instId = rfc1902.ObjectName(
-                        '.'.join([str(x) for x in self.__args[2:]])
-                    )
-                    self.__oid += instId
-                    self.__indices = (instId,)
-            self.__state |= self.ST_CLEAN
+                        '.'.join(str(x) for x in self._args[2:]))
+
+                    self._oid += instId
+
+                    self._indices = (instId,)
 
-            debug.logger & debug.FLAG_MIB and debug.logger('resolved indices are %r' % (self.__indices,))
+            self._state |= self.ST_CLEAN
+
+            debug.logger & debug.FLAG_MIB and debug.logger(
+                'resolved indices are %r' % (self._indices,))
 
             return self
+
         else:
             raise SmiError('Non-OID, label or MIB symbol')
 
     def prettyPrint(self):
-        if self.__state & self.ST_CLEAN:
+        if self._state & self.ST_CLEAN:
             s = rfc1902.OctetString()
+
             return '%s::%s%s%s' % (
-                self.__modName, self.__symName,
-                self.__indices and '.' or '',
-                '.'.join([x.isSuperTypeOf(s, matchConstraints=False) and '"%s"' % x.prettyPrint() or x.prettyPrint() for x in self.__indices])
-            )
+                self._modName, self._symName,
+                self._indices and '.' or '',
+                '.'.join((x.isSuperTypeOf(s, matchConstraints=False) and
+                          '"%s"' % x.prettyPrint() or
+                          x.prettyPrint()) for x in self._indices))
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def __repr__(self):
-        return '%s(%s)' % (self.__class__.__name__, ', '.join([repr(x) for x in self.__args]))
+        return '%s(%s)' % (self.__class__.__name__,
+                           ', '.join(repr(x) for x in self._args))
 
     # Redirect some attrs access to the OID object to behave alike
 
     def __str__(self):
-        if self.__state & self.ST_CLEAN:
-            return str(self.__oid)
+        if self._state & self.ST_CLEAN:
+            return str(self._oid)
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __eq__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid == other
+        if self._state & self.ST_CLEAN:
+            return self._oid == other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __ne__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid != other
+        if self._state & self.ST_CLEAN:
+            return self._oid != other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __lt__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid < other
+        if self._state & self.ST_CLEAN:
+            return self._oid < other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __le__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid <= other
+        if self._state & self.ST_CLEAN:
+            return self._oid <= other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __gt__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid > other
+        if self._state & self.ST_CLEAN:
+            return self._oid > other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __ge__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid > other
+        if self._state & self.ST_CLEAN:
+            return self._oid > other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __nonzero__(self):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid != 0
+        if self._state & self.ST_CLEAN:
+            return self._oid != 0
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __bool__(self):
-        if self.__state & self.ST_CLEAN:
-            return bool(self.__oid)
+        if self._state & self.ST_CLEAN:
+            return bool(self._oid)
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __getitem__(self, i):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid[i]
+        if self._state & self.ST_CLEAN:
+            return self._oid[i]
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __len__(self):
-        if self.__state & self.ST_CLEAN:
-            return len(self.__oid)
+        if self._state & self.ST_CLEAN:
+            return len(self._oid)
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __add__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return self.__oid + other
+        if self._state & self.ST_CLEAN:
+            return self._oid + other
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __radd__(self, other):
-        if self.__state & self.ST_CLEAN:
-            return other + self.__oid
+        if self._state & self.ST_CLEAN:
+            return other + self._oid
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __hash__(self):
-        if self.__state & self.ST_CLEAN:
-            return hash(self.__oid)
+        if self._state & self.ST_CLEAN:
+            return hash(self._oid)
+
         else:
-            raise SmiError('%s object not properly initialized' % self.__class__.__name__)
+            raise SmiError('%s object not properly '
+                           'initialized' % self.__class__.__name__)
 
     def __getattr__(self, attr):
-        if self.__state & self.ST_CLEAN:
+        if self._state & self.ST_CLEAN:
             if attr in ('asTuple', 'clone', 'subtype', 'isPrefixOf',
                         'isSameTypeWith', 'isSuperTypeOf', 'getTagSet',
                         'getEffectiveTagSet', 'getTagMap', 'tagSet', 'index'):
-                return getattr(self.__oid, attr)
+                return getattr(self._oid, attr)
+
             raise AttributeError(attr)
+
         else:
-            raise SmiError('%s object not properly initialized for accessing %s' % (self.__class__.__name__, attr))
+            raise SmiError(
+                '%s object not properly initialized for accessing '
+                '%s' % (self.__class__.__name__, attr))
 
 
-# A two-element sequence of ObjectIdentity and SNMP data type object
 class ObjectType(object):
     """Create an object representing MIB variable.
 
@@ -692,30 +789,35 @@ class ObjectType(object):
     ObjectType(ObjectIdentity('1.3.6.1.2.1.1.1.0'), Null(''))
     >>> ObjectType(ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0), 'Linux i386')
     ObjectType(ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0), 'Linux i386')
-
     """
     ST_DIRTY, ST_CLEAM = 1, 2
 
     def __init__(self, objectIdentity, objectSyntax=rfc1905.unSpecified):
         if not isinstance(objectIdentity, ObjectIdentity):
-            raise SmiError('initializer should be ObjectIdentity instance, not %r' % (objectIdentity,))
-        self.__args = [objectIdentity, objectSyntax]
-        self.__state = self.ST_DIRTY
+            raise SmiError(
+                'initializer should be ObjectIdentity instance, '
+                'not %r' % (objectIdentity,))
+
+        self._args = [objectIdentity, objectSyntax]
+        self._state = self.ST_DIRTY
 
     def __getitem__(self, i):
-        if self.__state & self.ST_CLEAM:
-            return self.__args[i]
+        if self._state & self.ST_CLEAM:
+            return self._args[i]
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def __str__(self):
         return self.prettyPrint()
 
     def __repr__(self):
-        return '%s(%s)' % (self.__class__.__name__, ', '.join([repr(x) for x in self.__args]))
+        return '%s(%s)' % (self.__class__.__name__,
+                           ', '.join([repr(x) for x in self._args]))
 
     def isFullyResolved(self):
-        return self.__state & self.ST_CLEAM
+        return self._state & self.ST_CLEAM
 
     def addAsn1MibSource(self, *asn1Sources, **kwargs):
         """Adds path to a repository to search ASN.1 MIB files.
@@ -747,7 +849,7 @@ class ObjectType(object):
         >>>
 
         """
-        self.__args[0].addAsn1MibSource(*asn1Sources, **kwargs)
+        self._args[0].addAsn1MibSource(*asn1Sources, **kwargs)
         return self
 
     def addMibSource(self, *mibSources):
@@ -779,7 +881,7 @@ class ObjectType(object):
         >>>
 
         """
-        self.__args[0].addMibSource(*mibSources)
+        self._args[0].addMibSource(*mibSources)
         return self
 
     def loadMibs(self, *modNames):
@@ -803,7 +905,7 @@ class ObjectType(object):
         >>>
 
         """
-        self.__args[0].loadMibs(*modNames)
+        self._args[0].loadMibs(*modNames)
         return self
 
     def resolveWithMib(self, mibViewController):
@@ -842,50 +944,61 @@ class ObjectType(object):
         >>>
 
         """
-        if self.__state & self.ST_CLEAM:
+        if self._state & self.ST_CLEAM:
             return self
 
-        self.__args[0].resolveWithMib(mibViewController)
+        self._args[0].resolveWithMib(mibViewController)
 
-        MibScalar, MibTableColumn = mibViewController.mibBuilder.importSymbols('SNMPv2-SMI', 'MibScalar',
-                                                                               'MibTableColumn')
+        MibScalar, MibTableColumn = mibViewController.mibBuilder.importSymbols(
+            'SNMPv2-SMI', 'MibScalar', 'MibTableColumn')
 
-        if not isinstance(self.__args[0].getMibNode(),
+        if not isinstance(self._args[0].getMibNode(),
                           (MibScalar, MibTableColumn)):
-            if not isinstance(self.__args[1], AbstractSimpleAsn1Item):
-                raise SmiError('MIB object %r is not OBJECT-TYPE (MIB not loaded?)' % (self.__args[0],))
-            self.__state |= self.ST_CLEAM
+            if not isinstance(self._args[1], AbstractSimpleAsn1Item):
+                raise SmiError('MIB object %r is not OBJECT-TYPE '
+                               '(MIB not loaded?)' % (self._args[0],))
+
+            self._state |= self.ST_CLEAM
+
             return self
 
-        if isinstance(self.__args[1], (rfc1905.UnSpecified,
-                                       rfc1905.NoSuchObject,
-                                       rfc1905.NoSuchInstance,
-                                       rfc1905.EndOfMibView)):
-            self.__state |= self.ST_CLEAM
+        if isinstance(self._args[1], (rfc1905.UnSpecified,
+                                      rfc1905.NoSuchObject,
+                                      rfc1905.NoSuchInstance,
+                                      rfc1905.EndOfMibView)):
+            self._state |= self.ST_CLEAM
             return self
 
+        syntax = self._args[0].getMibNode().getSyntax()
+
         try:
-            self.__args[1] = self.__args[0].getMibNode().getSyntax().clone(self.__args[1])
+            self._args[1] = syntax.clone(self._args[1])
+
         except PyAsn1Error as exc:
-            raise SmiError('MIB object %r having type %r failed to cast value %r: %s' % (
-                self.__args[0].prettyPrint(), self.__args[0].getMibNode().getSyntax().__class__.__name__, self.__args[1],
-                exc))
+            raise SmiError(
+                'MIB object %r having type %r failed to cast value '
+                '%r: %s' % (self._args[0].prettyPrint(),
+                            syntax.__class__.__name__, self._args[1], exc))
 
-        if rfc1902.ObjectIdentifier().isSuperTypeOf(self.__args[1], matchConstraints=False):
-            self.__args[1] = ObjectIdentity(self.__args[1]).resolveWithMib(mibViewController)
+        if rfc1902.ObjectIdentifier().isSuperTypeOf(
+                self._args[1], matchConstraints=False):
+            self._args[1] = ObjectIdentity(
+                self._args[1]).resolveWithMib(mibViewController)
 
-        self.__state |= self.ST_CLEAM
+        self._state |= self.ST_CLEAM
 
-        debug.logger & debug.FLAG_MIB and debug.logger('resolved %r syntax is %r' % (self.__args[0], self.__args[1]))
+        debug.logger & debug.FLAG_MIB and debug.logger(
+            'resolved %r syntax is %r' % (self._args[0], self._args[1]))
 
         return self
 
     def prettyPrint(self):
-        if self.__state & self.ST_CLEAM:
-            return '%s = %s' % (self.__args[0].prettyPrint(),
-                                self.__args[1].prettyPrint())
+        if self._state & self.ST_CLEAM:
+            return '%s = %s' % (self._args[0].prettyPrint(),
+                                self._args[1].prettyPrint())
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
 
 class NotificationType(object):
@@ -956,22 +1069,29 @@ class NotificationType(object):
 
     def __init__(self, objectIdentity, instanceIndex=(), objects={}):
         if not isinstance(objectIdentity, ObjectIdentity):
-            raise SmiError('initializer should be ObjectIdentity instance, not %r' % (objectIdentity,))
-        self.__objectIdentity = objectIdentity
-        self.__instanceIndex = instanceIndex
-        self.__objects = objects
-        self.__varBinds = []
-        self.__additionalVarBinds = []
-        self.__state = self.ST_DIRTY
+            raise SmiError(
+                'initializer should be ObjectIdentity instance, not '
+                '%r' % (objectIdentity,))
+
+        self._objectIdentity = objectIdentity
+        self._instanceIndex = instanceIndex
+        self._objects = objects
+        self._varBinds = []
+        self._additionalVarBinds = []
+        self._state = self.ST_DIRTY
 
     def __getitem__(self, i):
-        if self.__state & self.ST_CLEAN:
-            return self.__varBinds[i]
+        if self._state & self.ST_CLEAN:
+            return self._varBinds[i]
+
         else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+            raise SmiError(
+                '%s object not fully initialized' % self.__class__.__name__)
 
     def __repr__(self):
-        return '%s(%r, %r, %r)' % (self.__class__.__name__, self.__objectIdentity, self.__instanceIndex, self.__objects)
+        return '%s(%r, %r, %r)' % (
+            self.__class__.__name__, self._objectIdentity,
+            self._instanceIndex, self._objects)
 
     def addVarBinds(self, *varBinds):
         """Appends variable-binding to notification.
@@ -999,13 +1119,17 @@ class NotificationType(object):
         >>> nt.addVarBinds(ObjectType(ObjectIdentity('SNMPv2-MIB', 'sysDescr', 0)))
         NotificationType(ObjectIdentity('IP-MIB', 'linkDown'), (), {})
         >>>
-
         """
-        debug.logger & debug.FLAG_MIB and debug.logger('additional var-binds: %r' % (varBinds,))
-        if self.__state & self.ST_CLEAN:
-            raise SmiError('%s object is already sealed' % self.__class__.__name__)
+        debug.logger & debug.FLAG_MIB and debug.logger(
+            'additional var-binds: %r' % (varBinds,))
+
+        if self._state & self.ST_CLEAN:
+            raise SmiError(
+                '%s object is already sealed' % self.__class__.__name__)
+
         else:
-            self.__additionalVarBinds.extend(varBinds)
+            self._additionalVarBinds.extend(varBinds)
+
         return self
 
     def addAsn1MibSource(self, *asn1Sources, **kwargs):
@@ -1036,9 +1160,8 @@ class NotificationType(object):
         >>> NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {}).addAsn1Source('http://mibs.snmplabs.com/asn1/@mib@')
         NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {})
         >>>
-
         """
-        self.__objectIdentity.addAsn1MibSource(*asn1Sources, **kwargs)
+        self._objectIdentity.addAsn1MibSource(*asn1Sources, **kwargs)
         return self
 
     def addMibSource(self, *mibSources):
@@ -1068,9 +1191,8 @@ class NotificationType(object):
         >>> NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {}).addMibSource('/opt/pysnmp/mibs', 'pysnmp_mibs')
         NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {})
         >>>
-
         """
-        self.__objectIdentity.addMibSource(*mibSources)
+        self._objectIdentity.addMibSource(*mibSources)
         return self
 
     def loadMibs(self, *modNames):
@@ -1092,13 +1214,12 @@ class NotificationType(object):
         >>> NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {}).loadMibs('IF-MIB', 'TCP-MIB')
         NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {})
         >>>
-
         """
-        self.__objectIdentity.loadMibs(*modNames)
+        self._objectIdentity.loadMibs(*modNames)
         return self
 
     def isFullyResolved(self):
-        return self.__state & self.ST_CLEAN
+        return self._state & self.ST_CLEAN
 
     def resolveWithMib(self, mibViewController):
         """Perform MIB variable ID conversion and notification objects expansion.
@@ -1136,57 +1257,71 @@ class NotificationType(object):
         >>> notificationType.resolveWithMib(mibViewController)
         NotificationType(ObjectIdentity('IF-MIB', 'linkDown'), (), {})
         >>>
-
         """
-        if self.__state & self.ST_CLEAN:
+        if self._state & self.ST_CLEAN:
             return self
 
-        self.__objectIdentity.resolveWithMib(mibViewController)
+        self._objectIdentity.resolveWithMib(mibViewController)
 
-        self.__varBinds.append(
+        self._varBinds.append(
             ObjectType(ObjectIdentity(v2c.apiTrapPDU.snmpTrapOID),
-                       self.__objectIdentity).resolveWithMib(mibViewController)
-        )
+                       self._objectIdentity).resolveWithMib(mibViewController))
 
-        SmiNotificationType, = mibViewController.mibBuilder.importSymbols('SNMPv2-SMI', 'NotificationType')
+        SmiNotificationType, = mibViewController.mibBuilder.importSymbols(
+            'SNMPv2-SMI', 'NotificationType')
 
-        mibNode = self.__objectIdentity.getMibNode()
+        mibNode = self._objectIdentity.getMibNode()
 
         varBindsLocation = {}
 
         if isinstance(mibNode, SmiNotificationType):
+
             for notificationObject in mibNode.getObjects():
-                objectIdentity = ObjectIdentity(*notificationObject + self.__instanceIndex).resolveWithMib(
-                    mibViewController)
-                self.__varBinds.append(
-                    ObjectType(objectIdentity,
-                               self.__objects.get(notificationObject, rfc1905.unSpecified)).resolveWithMib(
-                        mibViewController)
-                )
-                varBindsLocation[objectIdentity] = len(self.__varBinds) - 1
+                objectIdentity = ObjectIdentity(
+                    *notificationObject + self._instanceIndex)
+
+                objectIdentity.resolveWithMib(mibViewController)
+
+                objectType = ObjectType(
+                    objectIdentity, self._objects.get(
+                        notificationObject, rfc1905.unSpecified))
+
+                objectType.resolveWithMib(mibViewController)
+
+                self._varBinds.append(objectType)
+
+                varBindsLocation[objectIdentity] = len(self._varBinds) - 1
+
         else:
             debug.logger & debug.FLAG_MIB and debug.logger(
-                'WARNING: MIB object %r is not NOTIFICATION-TYPE (MIB not loaded?)' % (self.__objectIdentity,))
+                'WARNING: MIB object %r is not NOTIFICATION-TYPE (MIB not '
+                'loaded?)' % (self._objectIdentity,))
 
-        for varBinds in self.__additionalVarBinds:
+        for varBinds in self._additionalVarBinds:
             if not isinstance(varBinds, ObjectType):
                 varBinds = ObjectType(ObjectIdentity(varBinds[0]), varBinds[1])
+
             varBinds.resolveWithMib(mibViewController)
+
             if varBinds[0] in varBindsLocation:
-                self.__varBinds[varBindsLocation[varBinds[0]]] = varBinds
+                self._varBinds[varBindsLocation[varBinds[0]]] = varBinds
+
             else:
-                self.__varBinds.append(varBinds)
+                self._varBinds.append(varBinds)
 
-        self.__additionalVarBinds = []
+        self._additionalVarBinds = []
 
-        self.__state |= self.ST_CLEAN
+        self._state |= self.ST_CLEAN
 
-        debug.logger & debug.FLAG_MIB and debug.logger('resolved %r into %r' % (self.__objectIdentity, self.__varBinds))
+        debug.logger & debug.FLAG_MIB and debug.logger(
+            'resolved %r into %r' % (self._objectIdentity, self._varBinds))
 
         return self
 
     def prettyPrint(self):
-        if self.__state & self.ST_CLEAN:
-            return ' '.join(['%s = %s' % (x[0].prettyPrint(), x[1].prettyPrint()) for x in self.__varBinds])
-        else:
-            raise SmiError('%s object not fully initialized' % self.__class__.__name__)
+        if self._state & self.ST_CLEAN:
+            return ' '.join('%s = %s' % (x[0].prettyPrint(), x[1].prettyPrint())
+                            for x in self._varBinds)
+
+        raise SmiError(
+            '%s object not fully initialized' % self.__class__.__name__)
diff --git a/pysnmp/smi/view.py b/pysnmp/smi/view.py
index e9fd405e..46ce5991 100644
--- a/pysnmp/smi/view.py
+++ b/pysnmp/smi/view.py
@@ -6,13 +6,6 @@
 #
 import sys
 
-from pysnmp import debug
-from pysnmp.smi import error
-from pysnmp.smi.indices import OidOrderedDict
-from pysnmp.smi.indices import OrderedDict
-
-__all__ = ['MibViewController']
-
 if sys.version_info[0] <= 2:
     import types
 
@@ -22,52 +15,69 @@ else:
     classTypes = (type,)
     instanceTypes = (object,)
 
+from pysnmp import debug
+from pysnmp.smi import error
+from pysnmp.smi.indices import OidOrderedDict
+from pysnmp.smi.indices import OrderedDict
+
+__all__ = ['MibViewController']
+
 
 class MibViewController(object):
     def __init__(self, mibBuilder):
         self.mibBuilder = mibBuilder
         self.lastBuildId = -1
-        self.__mibSymbolsIdx = OrderedDict()
+        self._mibSymbolsIdx = OrderedDict()
 
     # Indexing part
 
+    def _sortFun(self, name):
+        # This is potentially ambiguous mapping. Sort modules in
+        # ascending age for resolution
+        mb = self.mibBuilder
+
+        if mb.moduleID in mb.mibSymbols[name]:
+            mib = mb.mibSymbols[name][mb.moduleID]
+            revs = mib.getRevisions()
+            if revs:
+                return revs[0]
+
+        return '1970-01-01 00:00'
+
     def indexMib(self):
         if self.lastBuildId == self.mibBuilder.lastBuildId:
             return
 
-        debug.logger & debug.FLAG_MIB and debug.logger('indexMib: re-indexing MIB view')
+        debug.logger & debug.FLAG_MIB and debug.logger(
+            'indexMib: re-indexing MIB view')
 
         MibScalarInstance, = self.mibBuilder.importSymbols(
-            'SNMPv2-SMI', 'MibScalarInstance'
-        )
+            'SNMPv2-SMI', 'MibScalarInstance')
 
         #
         # Create indices
         #
 
         # Module name -> module-scope indices
-        self.__mibSymbolsIdx.clear()
+        self._mibSymbolsIdx.clear()
 
-        # Oid <-> label indices
+        globMibMod = {
+            'oidToLabelIdx': OidOrderedDict(),
+            'labelToOidIdx': {},
+            'varToNameIdx': {},
+            'typeToModIdx': OrderedDict(),
+            'oidToModIdx': {}
+        }
 
-        # This is potentially ambiguous mapping. Sort modules in
-        # ascending age for resolution
-        def __sortFun(x, b=self.mibBuilder):
-            if b.moduleID in b.mibSymbols[x]:
-                m = b.mibSymbols[x][b.moduleID]
-                r = m.getRevisions()
-                if r:
-                    return r[0]
+        self._mibSymbolsIdx[''] = globMibMod
 
-            return "1970-01-01 00:00"
+        # Oid <-> label indices
 
-        modNames = list(self.mibBuilder.mibSymbols.keys())
-        modNames.sort(key=__sortFun)
+        modNames = sorted(self.mibBuilder.mibSymbols, key=self._sortFun)
 
         # Index modules names
-        for modName in [''] + modNames:
-            # Modules index
-            self.__mibSymbolsIdx[modName] = mibMod = {
+        for modName in modNames:
+            mibMod = {
                 'oidToLabelIdx': OidOrderedDict(),
                 'labelToOidIdx': {},
                 'varToNameIdx': {},
@@ -75,76 +85,93 @@ class MibViewController(object):
                 'oidToModIdx': {}
             }
 
-            if not modName:
-                globMibMod = mibMod
-                continue
+            self._mibSymbolsIdx[modName] = mibMod
 
             # Types & MIB vars indices
             for n, v in self.mibBuilder.mibSymbols[modName].items():
                 if n == self.mibBuilder.moduleID:  # do not index this
                     continue  # special symbol
+
                 if isinstance(v, classTypes):
                     if n in mibMod['typeToModIdx']:
                         raise error.SmiError(
-                            'Duplicate SMI type %s::%s, has %s' % (modName, n, mibMod['typeToModIdx'][n])
-                        )
+                            'Duplicate SMI type %s::%s, has '
+                            '%s' % (modName, n, mibMod['typeToModIdx'][n]))
+
                     globMibMod['typeToModIdx'][n] = modName
                     mibMod['typeToModIdx'][n] = modName
+
                 elif isinstance(v, instanceTypes):
                     if isinstance(v, MibScalarInstance):
                         continue
+
                     if n in mibMod['varToNameIdx']:
                         raise error.SmiError(
-                            'Duplicate MIB variable %s::%s has %s' % (modName, n, mibMod['varToNameIdx'][n])
-                        )
+                            'Duplicate MIB variable %s::%s has '
+                            '%s' % (modName, n, mibMod['varToNameIdx'][n]))
+
                     globMibMod['varToNameIdx'][n] = v.name
                     mibMod['varToNameIdx'][n] = v.name
-                    # Potentionally ambiguous mapping ahead
+
+                    # Potentially ambiguous mapping ahead
                     globMibMod['oidToModIdx'][v.name] = modName
                     mibMod['oidToModIdx'][v.name] = modName
                     globMibMod['oidToLabelIdx'][v.name] = (n,)
                     mibMod['oidToLabelIdx'][v.name] = (n,)
+
                 else:
                     raise error.SmiError(
-                        'Unexpected object %s::%s' % (modName, n)
-                    )
+                        'Unexpected object %s::%s' % (modName, n))
 
         # Build oid->long-label index
-        oidToLabelIdx = self.__mibSymbolsIdx['']['oidToLabelIdx']
-        labelToOidIdx = self.__mibSymbolsIdx['']['labelToOidIdx']
+        oidToLabelIdx = self._mibSymbolsIdx['']['oidToLabelIdx']
+        labelToOidIdx = self._mibSymbolsIdx['']['labelToOidIdx']
+
         prevOid = ()
         baseLabel = ()
-        for key in oidToLabelIdx.keys():
+
+        for key in oidToLabelIdx:
             keydiff = len(key) - len(prevOid)
+
             if keydiff > 0:
                 if prevOid:
                     if keydiff == 1:
                         baseLabel = oidToLabelIdx[prevOid]
+
                     else:
                         baseLabel += key[-keydiff:-1]
                 else:
                     baseLabel = ()
+
             elif keydiff < 0:
                 baseLabel = ()
                 keyLen = len(key)
+
                 i = keyLen - 1
+
                 while i:
                     k = key[:i]
+
                     if k in oidToLabelIdx:
                         baseLabel = oidToLabelIdx[k]
+
                         if i != keyLen - 1:
                             baseLabel += key[i:-1]
+
                         break
+
                     i -= 1
+
             # Build oid->long-label index
             oidToLabelIdx[key] = baseLabel + oidToLabelIdx[key]
+
             # Build label->oid index
             labelToOidIdx[oidToLabelIdx[key]] = key
             prevOid = key
 
         # Build module-scope oid->long-label index
-        for mibMod in self.__mibSymbolsIdx.values():
-            for oid in mibMod['oidToLabelIdx'].keys():
+        for mibMod in self._mibSymbolsIdx.values():
+            for oid in mibMod['oidToLabelIdx']:
                 mibMod['oidToLabelIdx'][oid] = oidToLabelIdx[oid]
                 mibMod['labelToOidIdx'][oidToLabelIdx[oid]] = oid
 
@@ -154,9 +181,11 @@ class MibViewController(object):
 
     def getOrderedModuleName(self, index):
         self.indexMib()
-        modNames = self.__mibSymbolsIdx.keys()
+
+        modNames = self._mibSymbolsIdx
         if modNames:
             return modNames[index]
+
         raise error.SmiError('No modules loaded at %s' % self)
 
     def getFirstModuleName(self):
@@ -167,69 +196,89 @@ class MibViewController(object):
 
     def getNextModuleName(self, modName):
         self.indexMib()
+
         try:
-            return self.__mibSymbolsIdx.nextKey(modName)
+            return self._mibSymbolsIdx.nextKey(modName)
+
         except KeyError:
             raise error.SmiError(
-                'No module next to %s at %s' % (modName, self)
-            )
+                'No module next to %s at %s' % (modName, self))
 
     # MIB tree node management
 
-    def __getOidLabel(self, nodeName, oidToLabelIdx, labelToOidIdx):
+    def _getOidLabel(self, nodeName, oidToLabelIdx, labelToOidIdx):
         """getOidLabel(nodeName) -> (oid, label, suffix)"""
         if not nodeName:
             return nodeName, nodeName, ()
+
         if nodeName in labelToOidIdx:
             return labelToOidIdx[nodeName], nodeName, ()
+
         if nodeName in oidToLabelIdx:
             return nodeName, oidToLabelIdx[nodeName], ()
+
         if len(nodeName) < 2:
             return nodeName, nodeName, ()
-        oid, label, suffix = self.__getOidLabel(
-            nodeName[:-1], oidToLabelIdx, labelToOidIdx
-        )
+
+        oid, label, suffix = self._getOidLabel(
+            nodeName[:-1], oidToLabelIdx, labelToOidIdx)
+
         suffix = suffix + nodeName[-1:]
+
         resLabel = label + tuple([str(x) for x in suffix])
         if resLabel in labelToOidIdx:
             return labelToOidIdx[resLabel], resLabel, ()
+
         resOid = oid + suffix
         if resOid in oidToLabelIdx:
             return resOid, oidToLabelIdx[resOid], ()
+
         return oid, label, suffix
 
     def getNodeNameByOid(self, nodeName, modName=''):
         self.indexMib()
-        if modName in self.__mibSymbolsIdx:
-            mibMod = self.__mibSymbolsIdx[modName]
+
+        if modName in self._mibSymbolsIdx:
+            mibMod = self._mibSymbolsIdx[modName]
+
         else:
             raise error.SmiError('No module %s at %s' % (modName, self))
-        oid, label, suffix = self.__getOidLabel(
-            nodeName, mibMod['oidToLabelIdx'], mibMod['labelToOidIdx']
-        )
+
+        oid, label, suffix = self._getOidLabel(
+            nodeName, mibMod['oidToLabelIdx'], mibMod['labelToOidIdx'])
+
         if oid == label:
             raise error.NoSuchObjectError(
-                str='Can\'t resolve node name %s::%s at %s' %
-                    (modName, nodeName, self)
-            )
+                str='Cannot resolve node name %s::%s at '
+                    '%s' % (modName, nodeName, self))
+
         debug.logger & debug.FLAG_MIB and debug.logger(
-            'getNodeNameByOid: resolved %s:%s -> %s.%s' % (modName, nodeName, label, suffix))
+            'getNodeNameByOid: resolved %s:%s -> '
+            '%s.%s' % (modName, nodeName, label, suffix))
+
         return oid, label, suffix
 
     def getNodeNameByDesc(self, nodeName, modName=''):
         self.indexMib()
-        if modName in self.__mibSymbolsIdx:
-            mibMod = self.__mibSymbolsIdx[modName]
+
+        if modName in self._mibSymbolsIdx:
+            mibMod = self._mibSymbolsIdx[modName]
+
         else:
             raise error.SmiError('No module %s at %s' % (modName, self))
+
         if nodeName in mibMod['varToNameIdx']:
             oid = mibMod['varToNameIdx'][nodeName]
+
         else:
             raise error.NoSuchObjectError(
-                str='No such symbol %s::%s at %s' % (modName, nodeName, self)
-            )
+                str='No such symbol %s::%s at '
+                    '%s' % (modName, nodeName, self))
+
         debug.logger & debug.FLAG_MIB and debug.logger(
-            'getNodeNameByDesc: resolved %s:%s -> %s' % (modName, nodeName, oid))
+            'getNodeNameByDesc: resolved %s:%s -> '
+            '%s' % (modName, nodeName, oid))
+
         return self.getNodeNameByOid(oid, modName)
 
     def getNodeName(self, nodeName, modName=''):
@@ -238,28 +287,36 @@ class MibViewController(object):
         try:
             # First try nodeName as an OID/label
             return self.getNodeNameByOid(nodeName, modName)
+
         except error.NoSuchObjectError:
             # ...on failure, try as MIB symbol
             oid, label, suffix = self.getNodeNameByDesc(nodeName[0], modName)
+
             # ...with trailing suffix
             return self.getNodeNameByOid(oid + suffix + nodeName[1:], modName)
 
     def getOrderedNodeName(self, index, modName=''):
         self.indexMib()
-        if modName in self.__mibSymbolsIdx:
-            mibMod = self.__mibSymbolsIdx[modName]
+
+        if modName in self._mibSymbolsIdx:
+            mibMod = self._mibSymbolsIdx[modName]
+
         else:
             raise error.SmiError('No module %s at %s' % (modName, self))
+
         if not mibMod['oidToLabelIdx']:
             raise error.NoSuchObjectError(
-                str='No variables at MIB module %s at %s' % (modName, self)
-            )
+                str='No variables at MIB module %s at '
+                    '%s' % (modName, self))
+
         try:
             oid, label = mibMod['oidToLabelIdx'].items()[index]
+
         except KeyError:
             raise error.NoSuchObjectError(
-                str='No symbol at position %s in MIB module %s at %s' % (index, modName, self)
-            )
+                str='No symbol at position %s in MIB module %s at '
+                    '%s' % (index, modName, self))
+
         return oid, label, ()
 
     def getFirstNodeName(self, modName=''):
@@ -272,55 +329,67 @@ class MibViewController(object):
         oid, label, suffix = self.getNodeName(nodeName, modName)
         try:
             return self.getNodeName(
-                self.__mibSymbolsIdx[modName]['oidToLabelIdx'].nextKey(oid) + suffix, modName
-            )
+                self._mibSymbolsIdx[modName]['oidToLabelIdx'].nextKey(oid) + suffix,
+                modName)
+
         except KeyError:
             raise error.NoSuchObjectError(
-                str='No name next to %s::%s at %s' % (modName, nodeName, self)
-            )
+                str='No name next to %s::%s at '
+                    '%s' % (modName, nodeName, self))
 
     def getParentNodeName(self, nodeName, modName=''):
         oid, label, suffix = self.getNodeName(nodeName, modName)
+
         if len(oid) < 2:
             raise error.NoSuchObjectError(
-                str='No parent name for %s::%s at %s' %
-                    (modName, nodeName, self)
-            )
+                str='No parent name for %s::%s at '
+                    '%s' % (modName, nodeName, self))
+
         return oid[:-1], label[:-1], oid[-1:] + suffix
 
     def getNodeLocation(self, nodeName, modName=''):
         oid, label, suffix = self.getNodeName(nodeName, modName)
-        return self.__mibSymbolsIdx['']['oidToModIdx'][oid], label[-1], suffix
+        return (self._mibSymbolsIdx['']['oidToModIdx'][oid], label[-1],
+                suffix)
 
     # MIB type management
 
     def getTypeName(self, typeName, modName=''):
         self.indexMib()
-        if modName in self.__mibSymbolsIdx:
-            mibMod = self.__mibSymbolsIdx[modName]
+
+        if modName in self._mibSymbolsIdx:
+            mibMod = self._mibSymbolsIdx[modName]
+
         else:
             raise error.SmiError(
-                'No module %s at %s' % (modName, self)
-            )
+                'No module %s at %s' % (modName, self))
+
         if typeName in mibMod['typeToModIdx']:
             m = mibMod['typeToModIdx'][typeName]
+
         else:
             raise error.NoSuchObjectError(
-                str='No such type %s::%s at %s' % (modName, typeName, self)
-            )
+                str='No such type %s::%s at '
+                    '%s' % (modName, typeName, self))
+
         return m, typeName
 
     def getOrderedTypeName(self, index, modName=''):
         self.indexMib()
-        if modName in self.__mibSymbolsIdx:
-            mibMod = self.__mibSymbolsIdx[modName]
+
+        if modName in self._mibSymbolsIdx:
+            mibMod = self._mibSymbolsIdx[modName]
+
         else:
             raise error.SmiError('No module %s at %s' % (modName, self))
+
         if not mibMod['typeToModIdx']:
             raise error.NoSuchObjectError(
-                str='No types at MIB module %s at %s' % (modName, self)
-            )
-        t = mibMod['typeToModIdx'].keys()[index]
+                str='No types at MIB module %s at '
+                    '%s' % (modName, self))
+
+        t = list(mibMod['typeToModIdx'])[index]
+
         return mibMod['typeToModIdx'][t], t
 
     def getFirstTypeName(self, modName=''):
@@ -331,9 +400,11 @@ class MibViewController(object):
 
     def getNextType(self, typeName, modName=''):
         m, t = self.getTypeName(typeName, modName)
+
         try:
-            return self.__mibSymbolsIdx[m]['typeToModIdx'].nextKey(t)
+            return self._mibSymbolsIdx[m]['typeToModIdx'].nextKey(t)
+
         except KeyError:
             raise error.NoSuchObjectError(
-                str='No type next to %s::%s at %s' % (modName, typeName, self)
-            )
+                str='No type next to %s::%s at '
+                    '%s' % (modName, typeName, self))
diff --git a/setup.py b/setup.py
index 1dd5c958..d805bb05 100644
--- a/setup.py
+++ b/setup.py
@@ -38,15 +38,15 @@ Topic :: Software Development :: Libraries :: Python Modules
 
 
 def howto_install_setuptools():
-    print("""
-   Error: You need setuptools Python package!
+    print("""\
+Error: You need setuptools Python package!
 
-   It's very easy to install it, just type:
+It's very easy to install it, just type:
 
-   wget https://bootstrap.pypa.io/ez_setup.py
-   python ez_setup.py
+wget https://bootstrap.pypa.io/ez_setup.py
+python ez_setup.py
 
-   Then you could make eggs from this package.
+Then you could make eggs from this package.
 """)
 
 
@@ -94,8 +94,8 @@ try:
             observed_version < required_version):
         print("ERROR: your wheels won't come out round with setuptools %s! "
               "Upgrade to %s and try again." % (
-                '.'.join([str(x) for x in observed_version]),
-                '.'.join([str(x) for x in required_version])))
+                '.'.join(str(x) for x in observed_version),
+                '.'.join(str(x) for x in required_version)))
         sys.exit(1)
 
     # NOTE(etingof): older setuptools fail at parsing python_version