Support python3.6

Corrects some warnings and adds tox config.  Adds DeprecationWarning
to the error category.   Large sweep for string literals w/ backslashes
as this is common in docstrings

Co-authored-by: Andrii Soldatenko
Fixes: #3886
Change-Id: Ia7c838dfbbe70b262622ed0803d581edc736e085
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/337

2 files changed, 37 insertions, 33 deletions

diff --git a/lib/sqlalchemy/util/compat.py b/lib/sqlalchemy/util/compat.py
index beffc8541..5c615b0bc 100644
--- a/lib/sqlalchemy/util/compat.py
+++ b/lib/sqlalchemy/util/compat.py
@@ -8,6 +8,7 @@
 """Handle Python version/platform incompatibilities."""
 
 import sys
+from contextlib import contextmanager
 
 try:
     import threading
@@ -231,35 +232,38 @@ def with_metaclass(meta, *bases):
     return metaclass('temporary_class', None, {})
 
 
-from contextlib import contextmanager
 
-try:
-    from contextlib import nested
-except ImportError:
-    # removed in py3k, credit to mitsuhiko for
-    # workaround
-
-    @contextmanager
-    def nested(*managers):
-        exits = []
-        vars = []
-        exc = (None, None, None)
-        try:
-            for mgr in managers:
-                exit = mgr.__exit__
-                enter = mgr.__enter__
-                vars.append(enter())
-                exits.append(exit)
-            yield vars
-        except:
-            exc = sys.exc_info()
-        finally:
-            while exits:
-                exit = exits.pop()
-                try:
-                    if exit(*exc):
-                        exc = (None, None, None)
-                except:
-                    exc = sys.exc_info()
-            if exc != (None, None, None):
-                reraise(exc[0], exc[1], exc[2])
+
+@contextmanager
+def nested(*managers):
+    """Implement contextlib.nested, mostly for unit tests.
+
+    As tests still need to run on py2.6 we can't use multiple-with yet.
+
+    Function is removed in py3k but also emits deprecation warning in 2.7
+    so just roll it here for everyone.
+
+    """
+
+    exits = []
+    vars = []
+    exc = (None, None, None)
+    try:
+        for mgr in managers:
+            exit = mgr.__exit__
+            enter = mgr.__enter__
+            vars.append(enter())
+            exits.append(exit)
+        yield vars
+    except:
+        exc = sys.exc_info()
+    finally:
+        while exits:
+            exit = exits.pop()
+            try:
+                if exit(*exc):
+                    exc = (None, None, None)
+            except:
+                exc = sys.exc_info()
+        if exc != (None, None, None):
+            reraise(exc[0], exc[1], exc[2])
diff --git a/lib/sqlalchemy/util/langhelpers.py b/lib/sqlalchemy/util/langhelpers.py
index 00572fca8..973de426c 100644
--- a/lib/sqlalchemy/util/langhelpers.py
+++ b/lib/sqlalchemy/util/langhelpers.py
@@ -221,7 +221,7 @@ class PluginLoader(object):
 
 
 def get_cls_kwargs(cls, _set=None):
-    """Return the full set of inherited kwargs for the given `cls`.
+    r"""Return the full set of inherited kwargs for the given `cls`.
 
     Probes a class's __init__ method, collecting all named arguments.  If the
     __init__ defines a \**kwargs catch-all, then the constructor is presumed
@@ -1006,7 +1006,7 @@ def asint(value):
 
 
 def coerce_kw_type(kw, key, type_, flexi_bool=True):
-    """If 'key' is present in dict 'kw', coerce its value to type 'type\_' if
+    r"""If 'key' is present in dict 'kw', coerce its value to type 'type\_' if
     necessary.  If 'flexi_bool' is True, the string '0' is considered false
     when coercing to boolean.
     """