whilst on Py3, reraise exceptions with the original traceback

2 files changed, 12 insertions, 2 deletions

diff --git a/CHANGES b/CHANGES
index 841b038..cbeab8b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -21,6 +21,8 @@ Revision 4.2.2
   push them into MIB modules globals(). This is to facilitate
   passing user infomation, such as DB connection handler, to MIB
   module namespace so it could be used by ManagedObjects implementations.
+- When running on Python3, SMI will re-raise exceptions with the original
+  traceback for easier diagnostics.
 - Fix to oneliner configuration routine that used to implicitly
   tag SNMPv1/v2c auth and transport LCD rows what resulted in
   huge delays when processing incoming messages wish large number
diff --git a/pysnmp/smi/instrum.py b/pysnmp/smi/instrum.py
index df392e4..c9cba39 100644
--- a/pysnmp/smi/instrum.py
+++ b/pysnmp/smi/instrum.py
@@ -211,7 +211,7 @@ class MibInstrumController:
                 except error.SmiError:
                     debug.logger & debug.flagIns and debug.logger('flipFlopFsm: fun %s failed %s for %s=%r' % (f, sys.exc_info()[1], name, val))
                     if myErr is None:  # Take the first exception
-                        myErr = sys.exc_info()[1]
+                        myErr = sys.exc_info()
                     status = 'err'
                     break
                 else:
@@ -220,7 +220,15 @@ class MibInstrumController:
                         outputNameVals.append((rval[0], rval[1]))
                 idx = idx + 1
         if myErr:
-            raise myErr
+            if sys.version_info[0] <= 2:
+                raise myErr[1]
+            else:
+                try:
+                    raise myErr[1].with_traceback(myErr[2])
+                finally:
+                    # Break cycle between locals and traceback object
+                    # (seems to be irrelevant on Py3 but just in case)
+                    del myErr
         return outputNameVals
     
     def readVars(self, vars, acInfo=(None, None)):