unittest's assertRaises removes locals from tracebacks

[blueyed]

BPO	39766
Nosy	@blueyed, @jacksonriley

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-02-26.22:01:11.668>
labels = ['3.8', '3.7', 'library', '3.9']
title = "unittest's assertRaises removes locals from tracebacks"
updated_at = <Date 2021-05-11.13:38:40.113>
user = 'https://github.com/blueyed'

bugs.python.org fields:

activity = <Date 2021-05-11.13:38:40.113>
actor = 'jacksonriley'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-02-26.22:01:11.668>
creator = 'blueyed'
dependencies = []
files = []
hgrepos = []
issue_num = 39766
keywords = []
message_count = 3.0
messages = ['362744', '362753', '393457']
nosy_count = 2.0
nosy_names = ['blueyed', 'jacksonriley']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue39766'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9']

[blueyed]

I was a bit surprised to find that unittest's assertRaises clears the locals on the traceback, which e.g. prevents pytest to display them in case of failures.

This was done via https://bugs.python.org/issue9815 (9681022).

Maybe this should only get done for expected failures, so that unexpected exceptions can be inspected better?

[blueyed]

The test for bpo-9815 passes since bbd3cf8 (bpo-23890).

It seems like traceback.clear_frames(tb) should probably removed altogether?

[jacksonriley]

+1 - I was surprised not to be able to get locals from many of the frames in pdb upon an unexpected exception being raised inside an assertRaises. Thanks for raising this issue Daniel.