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# Copyright 2013 Red Hat, Inc.
# All Rights Reserved.
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import pdb
import traceback
def exception_handler(exc_info):
"""Exception handler enabling post-mortem debugging.
A class extending testtools.TestCase can add this handler in setUp():
When an exception occurs, the user will be dropped into a pdb
session in the execution environment of the failure.
Frames associated with the testing framework are excluded so that
the post-mortem session for an assertion failure will start at the
assertion call (e.g. self.assertTrue) rather than the framework code
that raises the failure exception (e.g. the assertTrue method).
tb = exc_info[2]
ignored_traceback = get_ignored_traceback(tb)
if ignored_traceback:
tb = FilteredTraceback(tb, ignored_traceback)
traceback.print_exception(exc_info[0], exc_info[1], tb)
def get_ignored_traceback(tb):
"""Retrieve the first traceback of an ignored trailing chain.
Given an initial traceback, find the first traceback of a trailing
chain of tracebacks that should be ignored. The criteria for
whether a traceback should be ignored is whether its frame's
globals include the __unittest marker variable. This criteria is
culled from:
For example:
tb.tb_next => tb0.tb_next => tb1.tb_next
- If no tracebacks were to be ignored, None would be returned.
- If only tb1 was to be ignored, tb1 would be returned.
- If tb0 and tb1 were to be ignored, tb0 would be returned.
- If either of only tb or only tb0 was to be ignored, None would
be returned because neither tb or tb0 would be part of a
trailing chain of ignored tracebacks.
# Turn the traceback chain into a list
tb_list = []
while tb:
tb = tb.tb_next
# Find all members of an ignored trailing chain
ignored_tracebacks = []
for tb in reversed(tb_list):
if '__unittest' in tb.tb_frame.f_globals:
# Return the first member of the ignored trailing chain
if ignored_tracebacks:
return ignored_tracebacks[-1]
class FilteredTraceback(object):
"""Wraps a traceback to filter unwanted frames."""
def __init__(self, tb, filtered_traceback):
:param tb: The start of the traceback chain to filter.
:param filtered_traceback: The first traceback of a trailing
chain that is to be filtered.
self._tb = tb
self.tb_lasti = self._tb.tb_lasti
self.tb_lineno = self._tb.tb_lineno
self.tb_frame = self._tb.tb_frame
self._filtered_traceback = filtered_traceback
def tb_next(self):
tb_next = self._tb.tb_next
if tb_next and tb_next != self._filtered_traceback:
return FilteredTraceback(tb_next, self._filtered_traceback)