Errors with v49.2.0's distutils adoption

Related to #2256 / #2259.

When upgrading to setuptools>=49.1.3 for the https://github.com/pypa/setuptools/pull/2249 fix for Pillow, we get the new warning in v49.2.0:

/home/travis/virtualenv/python3.9-dev/lib/python3.9/site-packages/setuptools/distutils_patch.py:25: UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may exhibit undesirable behaviors or errors. Please use Setuptools’ objects directly or at least import Setuptools first.

This also causes some C build issues and this sanity test failure; Pillow checks the version in the lower-level C code (“Core version”) matches that in the user-facing Python code (“Pillow version”):

/home/travis/virtualenv/python3.9-dev/lib/python3.9/site-packages/Pillow-7.3.0.dev0-py3.9-linux-x86_64.egg/PIL/Image.py:115: RuntimeWarning: The _imaging extension was built for another version of Pillow or PIL: Core version: None Pillow version: 7.3.0.dev0

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Moving the setuptools import before distutils in our setup.py removes the warning but not the error.

https://travis-ci.org/github/hugovk/Pillow/builds/707730154

I’ve not dug into this further, but it’s happening at least on all the Linux/Python versions tested on Travis (3.5-3.9), and wanted to let you know.

More details at https://github.com/python-pillow/Pillow/pull/4784#issuecomment-657727387.

[hugovk]

One option to replace distutils.version is packaging.version.parse:

• https://stackoverflow.com/a/11887885/724176
• https://github.com/python-pillow/Pillow/pull/4797

[jaraco]

is there a firm commitment from setuptools that these (admittedly obscure) functions and attributes, that many projects depend on, will not change without a migration path and a clear deprecation cycle that matches the release cycle of the scientific python stack?

I wouldn’t say there’s a firm commitment, but I would say there is a strong commitment to helping the community transition off of distutils in the stdlib, preferably to something other than distutils, but providing distutils in the meantime in a compatible way and communicating changes through semver. Setuptools/distutils will rely heavily on the community (numpy, PyPy, and others) to contribute to the solution to provide the smoothest transition.

If more of a commitment is needed, please open an issue.