It'll probably be easier to change the warnings filter semantic 
(https://docs.python.org/3/library/warnings.html#the-warnings-filter)
to which those values are directly passed.

On 16.04.2021 16:07, Victor Stinner wrote:
Hi,

I propose to change the -W command line option and the PYTHONWARNINGS
environment variable to use the message as a regular expression in
Python 3.10. Or does anyone have a reason to keep the current behavior
as it is?

I created https://bugs.python.org/issue43862 for this change.

--

Python provides two ways to specify warnings filters:

* -W command line option: can be used multiple times
* PYTHONWARNINGS environment variable: can contain multiple options
separated by commas

While the Python API warnings.filterwarnings(action, message="", ...)
uses the message as a regular expression, -W and PYTHONWARNINGS
require to match *exactly* the *whole* message.

For example, if you only want to ignore the new distutils deprecation
warning, you must write exactly:

$ ./python -X dev -W 'ignore:The distutils package is deprecated and
slated for removal in Python 3.12. Use setuptools or check PEP 632 for
potential alternatives:DeprecationWarning' -c 'import distutils'

I use -X dev to show DeprecationWarning, or you can also use -Wdefault
if you prefer.

If the deprecation warning changes in Python or if you have a single
typo, the warning is not ignored. Example with a typo ("3.13" rather
than "3.12"):

$ ./python -X dev -W 'ignore:The distutils package is deprecated and
slated for removal in Python 3.13. Use setuptools or check PEP 632 for
potential alternatives:DeprecationWarning' -c 'import distutils'
<string>:1: DeprecationWarning: The distutils package is deprecated
and slated for removal in Python 3.12. Use setuptools or check PEP 632
for potential alternatives

The PYTHONWARNINGS has another limitation: you cannot specify a
message if it contains a comma (","). Hopefully, Python doesn't raise
warnings containing comma, right? Well... Just one example:

Lib/distutils/sysconfig.py:554:        warnings.warn('SO is
deprecated, use EXT_SUFFIX', DeprecationWarning, 2)

You cannot only ignore the message:

$ PYTHONWARNINGS='ignore:SO is deprecated, use
EXT_SUFFIX:DeprecationWarning' ./python -c 'import sys;
print(sys.warnoptions); print(len(sys.warnoptions))'
Invalid -W option ignored: invalid action: 'use EXT_SUFFIX'
['ignore:SO is deprecated', ' use EXT_SUFFIX:DeprecationWarning']
2

You can only try to use "module" and "lineno" parameters of a warning
filter, which are more fragile and hard to use to use.

Victor

--
Regards,
Ivan

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