Support regular expressions in `-W` and `PYTHONWARNINGS` · Issue #134716 · python/cpython · GitHub

Bug report

Bug description:

When the PYTHONWARNINGS message field contains a special character such as . or * it gets quoted as \. or \* so it looses it's regex meaning and never matches. I tested this in 3.8 and 3.13.

PYTHONWARNINGS='ignore:This.*deadlocks:DeprecationWarning' python -c 'import warnings; print(warnings.filters[0])'

yields:

('ignore', re.compile('This\\.\\*deadlocks', re.IGNORECASE), <class 'DeprecationWarning'>, None, 0)

(note the extra backslash is a result of the print statement, doing a repr.)

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

gh-134716: Support regular expressions in -W and PYTHONWARNINGS #138149

The docs say:

In -W and PYTHONWARNINGS, message is a literal string that the start of the warning message must contain (case-insensitively), ignoring any whitespace at the start or end of message

So I don't think we're meant to support regexes when using -W and PYTHONWARNINGS (but we can when we use the module directly)

Thank you for clarification.
My fault. The docs 3.10.7 indeed says -W and PYTHONWARNINGS is a literal string. Prior versions seem to lack this language:

The warnings filter is initialized by -W options passed to the Python interpreter command line and the PYTHONWARNINGS environment variable.
<snip>
Individual warnings filters are specified as a sequence of fields separated by colons:
action:message:category:module:line
The meaning of each of these fields is as described in The Warnings Filter.

See also #78805, #79101, #86438, #88028. There may be other duplicate issues.

Arf, my bad. I'll triage them tomorrow.

All of them were closed. AFAIK. only the documentation was updated.

But I had ideas on how to solve this problem differently, so we can leave this issue for that or reopen one of old issues if they contain more information.

pythongh-134716: Support regular expressions in -W and PYTHONWARNINGS

#138149 implements support of regular expressions. To differentiate them from literal strings, you must surround them by forward slashes.

Using the original example:

$ PYTHONWARNINGS='ignore:This.*deadlocks:DeprecationWarning' ./python -c 'import warnings; print(warnings.filters[0])'
('ignore', re.compile('This\\.\\*deadlocks', re.IGNORECASE), <class 'DeprecationWarning'>, None, 0)
$ PYTHONWARNINGS='ignore:/This.*deadlocks/:DeprecationWarning' ./python -c 'import warnings; print(warnings.filters[0])'
('ignore', re.compile('This.*deadlocks', re.IGNORECASE), <class 'DeprecationWarning'>, None, 0)

Previous issues which were closed after changing the documentation:

gh-134716: Support regular expressions in -W and PYTHONWARNINGS (GH-1…

Support regular expressions in `-W` and `PYTHONWARNINGS` · Issue #134716 · python/cpython · GitHub

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Support regular expressions in -W and PYTHONWARNINGS #134716

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Support regular expressions in `-W` and `PYTHONWARNINGS` · Issue #134716 · python/cpython · GitHub

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Support regular expressions in -W and PYTHONWARNINGS #134716

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Bug report

Bug description:

CPython versions tested on:

Operating systems tested on:

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picnixz commented on May 26, 2025

garyaviv commented on May 26, 2025

serhiy-storchaka commented on May 30, 2025

picnixz commented on May 30, 2025

serhiy-storchaka commented on May 30, 2025

serhiy-storchaka commented on Aug 25, 2025

serhiy-storchaka commented on Sep 15, 2025

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