[New-bugs-announce] [issue47074] Convenient `simplefilter()` in `warnings.catch_warnings()`

Zac Hatfield-Dodds report at bugs.python.org
Sun Mar 20 21:46:48 EDT 2022

New submission from Zac Hatfield-Dodds <zac.hatfield.dodds at gmail.com>:

Many pytest users would like a concise way to either suppress warnings, or convert them to errors [1].  The current best approach is:

    with warnings.catch_warnings():
        warnings.simplefilter("ignore")  # or "error"

but even this becomes tediously verbose when repeated in hundreds of tests (which I suspect is responsible for many misuses of `pytest.raises()`).  Since these two functions take disjoint arguments [2], I propose allowing catch_warnings() to accept arguments for simplefilter() and forward them on:

    with warnings.catch_warnings("ignore"):  # or "error"

I have a quick implementation at [3] which I can finish if the idea is acceptable.  Although I don't have a concrete use-case for more than the 'action' and 'category' arguments, forwarding all rather than some makes the semantics very simple.

I'd emphasize again that this is very much a convenience-focussed change: I estimate that 95% of all uses will pass only `action="error"` or `action="ignore"`.  Supporting a concise and simple interface for this seems worth the small complication to the design of the warnings module.

[1] see e.g. https://github.com/pytest-dev/pytest/issues/9404 for a long thread
[2] unlike `filterwarnings()`, which has a `module=` argument which would collide with `catch_warnings()`
[3] https://github.com/python/cpython/compare/main...Zac-HD:zac-hd/one-line-catch-warnings

components: Library (Lib)
messages: 415647
nosy: Zac Hatfield-Dodds
priority: normal
severity: normal
status: open
title: Convenient `simplefilter()` in `warnings.catch_warnings()`
type: enhancement
versions: Python 3.11

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