PEP 632 - Deprecate distutils module

ferdnyc · November 29, 2020, 9:38pm

hroncok:

Status quo

Both distributions currently patch distutils.command.install.INSTALL_SCHEMES and have custom logic for selecting the appropriate scheme.

The Fedora patch is minimal yet “hacked”.

The Debian patch is more complex yet more systematic.

Both patches are designed for the same purpose: When the Python packages are installed by users (e.g. via sudo), they are installed to a location that is not managed by the system package manager (i.e. /usr/local/lib(64)?/pythonX.Y/(site|dist)-packages ). When the Python packages are installed to a fake --root by the system package manager build scripts (e.g. rpmbuild ), they are installed to the system location (i.e. /path/to/buildroot/usr/lib64/pythonX.Y/(site|dist)-packages , so the system packages ( .deb or .rpm ) are installed to /usr/lib(64)?/pythonX.Y/(site|dist)-packages ). The site module is also patched to ensure proper sys.path .

I wouldn’t judge Fedora’s “hacked” patch too harshly — there’s something to be said for the simpler approach. Debian’s patch is far more comprehensive, yes, but that’s exactly what gets it into trouble.

When third-party install scripts/tools go to install Python modules, many use the path returned by distutils.sysconfig.get_python_lib(prefix="/usr/local/") as their target path (if building for the default /usr/local install prefix).

On Fedora, that call returns /usr/local/lib/python3.x/site-packages, which will be in the default sys.path if the directory exists. All is well.
Debian’s patched distutils will instead return /usr/local/lib/python3/dist-packages, a path that is not added to sys.path under any circumstances (except manually). That path is also incorrect based on their own documentation. (As you say, the path should be /usr/local/lib/python3.x/dist-packages.)

This has occasionally been a source of some consternation among maintainers and distributors of Python software.

(setuptools on Debian-based systems uses correct paths, though. So in a roundabout way this is just another point in favor of deprecating broken distutils, and instead using the better-maintained setuptools wherever possible.)