Merge pull request #3152 from brianmaissy/silently_fail_to_import_during_postmortem

If we fail to import doctest.UnexpectedException during postmortem, fail quietly

_pytest/debugging.py

@@ -2,6 +2,7 @@
 from __future__ import absolute_import, division, print_function
 import pdb
 import sys
+from doctest import UnexpectedException
 
 
 def pytest_addoption(parser):
@@ -95,10 +96,9 @@ def _enter_pdb(node, excinfo, rep):
 
 
 def _postmortem_traceback(excinfo):
-    # A doctest.UnexpectedException is not useful for post_mortem.
-    # Use the underlying exception instead:
-    from doctest import UnexpectedException
     if isinstance(excinfo.value, UnexpectedException):
+        # A doctest.UnexpectedException is not useful for post_mortem.
+        # Use the underlying exception instead:
         return excinfo.value.exc_info[2]
     else:
         return excinfo._excinfo[2]

changelog/1810.bugfix

@@ -0,0 +1 @@
+Move import of ``doctest.UnexpectedException`` to top-level to avoid possible errors when using ``--pdb``.