warnings.simplefilter should validate input

[seberg]

BPO	16845
Nosy	@berkerpeksag, @seberg, @vajrasky, @nanjekyejoannah, @Bonifacio2, @DanielNoord
PRs	bpo-16845: add category type check to warnings.simplefilter #26696 bpo-16845: Validate the category of warnings.simplefilter sooner #31983
Files	add_assert_in_simplefilter.patch issue16845.diff

^{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 2013-01-03.00:42:06.501>
labels = ['easy', 'type-feature', 'library', '3.10']
title = 'warnings.simplefilter should validate input'
updated_at = <Date 2022-03-18.19:52:15.032>
user = 'https://github.com/seberg'

bugs.python.org fields:

activity = <Date 2022-03-18.19:52:15.032>
actor = 'danielnoord'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2013-01-03.00:42:06.501>
creator = 'seberg'
dependencies = []
files = ['32131', '35773']
hgrepos = []
issue_num = 16845
keywords = ['patch', 'easy']
message_count = 5.0
messages = ['178867', '199985', '221480', '395747', '415522']
nosy_count = 7.0
nosy_names = ['python-dev', 'berker.peksag', 'seberg', 'vajrasky', 'nanjekyejoannah', 'Bonifacio2', 'danielnoord']
pr_nums = ['26696', '31983']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue16845'
versions = ['Python 3.10']

[seberg]

warnings.simplefilter does not validate that the category passed in is actually a class. This means that an invalid category leads to a TypeError whenever a warning would otherwise occur due to issubclass check failing.

It is a very small thing, but for usability it would be clearer if this was checked right away.

[vajrasky]

Here is the patch to add the validation in simplefilter with the test.

[berkerpeksag]

Here's a patch that uses the same approach as in bpo-16382.

[nanjekyejoannah]

@Bonifacio2, As commented on the PR, I think opening a PR with a patch close to what @berker.peksag suggested looks more elaborate, IMHO.

Thanks for your contribution.

[DanielNoord]

I have submitted the path by @berker.peksag with one additional test case in a new PR.

@nanjekyejoannah I saw you responded to the other PR, but that died down. Would you mind taking a look at mine? I'm happy to help land this :)

[DanielNoord]

See #31983.

I see no reason to pursue this. warnings.simplefilter("error", int) does not raise a TypeError later on, even when warnings a raised. Adding validation only makes this unnecessarily stricter while that is not needed. The documentation is clear that Warning classes are preferred.

[encukou]

I agree.