Setuptools warning: License classifiers are deprecated

[hhoffstaette]

Packaging fun 🙄

Accidentally noticed the following:

>>> Compiling source in /tmp/portage/dev-python/btrfs-15/work/python-btrfs-15 ...
 * python3_14: running distutils-r1_run_phase distutils-r1_python_compile
 *   Building the wheel for python-btrfs-15 via setuptools.build_meta:__legacy__
python3.14 -m gpep517 build-wheel --prefix=/usr --backend setuptools.build_meta:__legacy__ --output-fd 3 --wheel-dir /tmp/portage/dev-python/btrfs-15/work/python-btrfs-15-python3_14/wheel
2026-05-06 10:19:45,606 gpep517 INFO Building wheel via backend setuptools.build_meta:__legacy__
/usr/lib/python3.14/site-packages/setuptools/dist.py:765: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: GNU Lesser General Public License v3 (LGPLv3)

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!
  self._finalize_license_expression()

I have only a cursory understanding about what's going on here, but apparently this means this line is supposed to be removed and replaced with the new way of declaring things.

Also see pypa/setuptools#4938

[hhoffstaette]

I managed to yolo something together in hhoffstaette/portage@2894732, maybe that helps.

[knorrie]

Hi Holger!

Thanks for reporting. I just had a look at it.
It seems that if I just want to make changes to the setup.py file, it means removing that one line and adding a license field with a SPDX license identifier, which is LGPL-3.0-or-later in this case.

I added a commit in the develop branch and also checked here that I first got the warning, then no warning and that License: LGPL-3.0-or-later also shows up in the resulting PKG-INFO.

If it helps you, I can do a v15.1 release. There's also a few other fixes waiting.

Hans

[hhoffstaette]

I added a commit in the develop branch and also checked here that I first got the warning, then no warning and that License: LGPL-3.0-or-later also shows up in the resulting PKG-INFO.

Nice! Much easier than creating a setup.cfg. (I know next to nothing about py packaging).

If it helps you, I can do a v15.1 release. There's also a few other fixes waiting.

Thanks but it's not urgent (for me). v15 has been working well without any problems since last year. I only found it because someone in one of Gentoo's IRC channels noticed the same thing in a different package and we discussed it.