Warnings stacklevel frames to skip

[jimjjewett]

BPO	25216
Nosy	@JimJJewett, @jayvdb

^{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 2015-09-22.15:47:00.527>
labels = ['type-feature', 'library']
title = 'Warnings stacklevel frames to skip'
updated_at = <Date 2015-12-10.08:16:01.708>
user = 'https://github.com/JimJJewett'

bugs.python.org fields:

activity = <Date 2015-12-10.08:16:01.708>
actor = 'jayvdb'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2015-09-22.15:47:00.527>
creator = 'Jim.Jewett'
dependencies = []
files = []
hgrepos = []
issue_num = 25216
keywords = []
message_count = 2.0
messages = ['251328', '256169']
nosy_count = 2.0
nosy_names = ['Jim.Jewett', 'jayvdb']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue25216'
versions = ['Python 3.6']

[jimjjewett]

warnings.warn(stacklevel=2) is a longstanding idiom.

It broke in 3.3 because python itself added some additional infrastructure frames in between; now stacklevel should be 8 or 10 in some releases.

bpo-24305 adds a workaround for 3.5, to ignore internal frames -- defined as those which contain both 'importlib' and '_bootstrap' in filename.

I would prefer to see a supported hook, so that either the caller or the program setup could list other modules or packages to ignore when counting frames. That way, I could write

mycall(otherlib(foo))

and otherlib could ensure that the warning pointed to mycall, rather than to something internal to otherlib, even if otherlib were refactored to a different stack depth.

Ignoring just the import machinery would of course be a good default.

[jayvdb]

This looks a lot like the patch on http://bugs.python.org/issue850482 aka #39615

[gpshead]

duplicate of #39615