testExceptionCleanupNames doesn't test anything?

[yellowdusk1590]

BPO	46442
Nosy	@ericvsmith, @JelleZijlstra, @miss-islington, @sobolevn, @yellowdusk1590
PRs	bpo-46442: improve testExceptionCleanupNames #30753 bpo-46442: improve testExceptionCleanupNames #30758 [3.10] bpo-46442: improve and rename testExceptionCleanupNames (GH-30758) #30778 [3.9] bpo-46442: improve and rename testExceptionCleanupNames (GH-30758) #30779

^{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 = <Date 2022-01-22.08:14:43.756>
created_at = <Date 2022-01-20.00:33:05.618>
labels = ['tests', '3.11']
title = "testExceptionCleanupNames doesn't test anything?"
updated_at = <Date 2022-01-22.08:14:43.755>
user = 'https://github.com/yellowdusk1590'

bugs.python.org fields:

activity = <Date 2022-01-22.08:14:43.755>
actor = 'eric.smith'
assignee = 'none'
closed = True
closed_date = <Date 2022-01-22.08:14:43.756>
closer = 'eric.smith'
components = ['Tests']
creation = <Date 2022-01-20.00:33:05.618>
creator = 'yellowdusk1590'
dependencies = []
files = []
hgrepos = []
issue_num = 46442
keywords = ['patch']
message_count = 8.0
messages = ['410997', '411029', '411040', '411146', '411233', '411234', '411235', '411236']
nosy_count = 5.0
nosy_names = ['eric.smith', 'JelleZijlstra', 'miss-islington', 'sobolevn', 'yellowdusk1590']
pr_nums = ['30753', '30758', '30778', '30779']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46442'
versions = ['Python 3.11']

[yellowdusk1590]

testExceptionCleanupNames() is supposed to test that the local variable bound to the exception instance is only visible inside the except block, and tests that by checking whether the name is in locals(), but it actually deletes the name before that, so it appears it isn't testing what it's supposed to be testing.

        try:
            raise Exception()
        except Exception as e:
            self.assertTrue(e)
            del e
        self.assertNotIn('e', locals())

[ericvsmith]

I don't know for sure, but maybe it's trying to test "del" interacting with the fact that the "as e" part doesn't escape the "except" clause, unlike normal assignments:

>>> try:
...     raise Exception
... except Exception as e:
...     print('exception raised')
...     foo = 1
...
exception raised
>>> foo
1
>>> e
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'e' is not defined

[JelleZijlstra]

Perhaps it's testing that the implicit del doesn't blow up if the variable is already deleted.

[yellowdusk1590]

Great point, it's indeed a good thing to test. So I guess the test is just incomplete.

[ericvsmith]

New changeset 82c5322 by Yellow Dusk in branch 'main':
bpo-46442: improve and rename testExceptionCleanupNames (GH-30758)
82c5322

[miss-islington]

New changeset d4a9e34 by Miss Islington (bot) in branch '3.10':
bpo-46442: improve and rename testExceptionCleanupNames (GH-30758)
d4a9e34

[miss-islington]

New changeset e064af5 by Miss Islington (bot) in branch '3.9':
bpo-46442: improve and rename testExceptionCleanupNames (GH-30758)
e064af5

[ericvsmith]

Thanks, @yellowdusk1590!