Hi,

This command does not report a warning, while it should:

  python -c 'import warnings; warnings.warn("This should show up")' -Wi -W'default:::.*'

If the regex `.*` is replaced by `__main__` it works as expected.

Same applies for regexes in PYTHONWARNINGS and for the `message` part of the argument. 

The reason can be found in Lib/warnings.py:144 (def _setoption):

  module = re.escape(module)

This point-blank escape makes me think that it was intended that no regexes can be passed to message/module. On the other, the documentation reads as if it should be supported.

Specifically, the -W option is documented in [1]. While this page lists only basic examples, it refers to [2] and [3] for more details. [2] states that message/module are regexes. [3] seems to be written to specifically address the syntax of the PYTHONWARNINGS and the -W option and explicitly lists an example with a regex.

[1]: https://docs.python.org/3/using/cmdline.html#cmdoption-w
[2]: https://docs.python.org/3/library/warnings.html#warning-filter
[3]: https://docs.python.org/3/library/warnings.html#describing-warning-filters

I would welcome if we could remove `re.escape` to make the implementation fit the documentation, or are there any downsides to this?


Best regards, Thomas