bpo-1294959 added sys.platlibdir and configure --with-platlibdir to use /usr/lib64 on Fedora and SuSE to Python 3.9. The problem is that https://bugs.python.org/issue40854#msg370655 use case seems to be a regression compared to Python 3.9.

I now consider to backport the commit 8f023a2 to 3.9 since it looks like a fix part of bpo-1294959 rather than a bug fix.

I created this PR to backport PyConfig.platlibdir and PYTHONPLATLIBDIR env var to Python 3.9.

@ambv: Are you ok to include this change in Python 3.9 final?

cc @hroncok @mcepl @stratakis

If this PR is merged, the documentation must be updated in the master branch to replace "3.9" with "3.10" (as I did in this backport).

I'm fine with this landing in 3.9.0 but unless it lands within the next hour or so it will miss Beta 2.

LGTM, but, boy, this is getting really complicated! Originally, it was just a simple few lines hack …

+1

LGTM, but, boy, this is getting really complicated! Originally, it was just a simple few lines hack …

A hack is acceptable for a downstream patch. But upstream, we usually write things differently and it requires more work. Also, when a feature is made upstream, new corner cases are discovered :-)

See also https://bugs.python.org/issue40684 "make install doesn't respect configure --with-platlibdir=lib64".

I'm fine with this landing in 3.9.0 but unless it lands within the next hour or so it will miss Beta 2.

Ok, I merged my PR. Thanks @ambv ;-)

If this PR is merged, the documentation must be updated in the master branch to replace "3.9" with "3.10" (as I did in this backport).

I created PR #20735.