sysconfig.get_path('platstdlib') return paths in virtual environments (or otherwise weird)

[hroncok]

Bug report

The sysconfig.get_path function is supposed to return he following for its first argument:

• stdlib: directory containing the standard Python library files that are not platform-specific.
• platstdlib: directory containing the standard Python library files that are platform-specific.

E.g. in the python:3.11.1 Docker container:

>>> import sysconfig
>>> sysconfig.get_path('stdlib')
'/usr/local/lib/python3.11'
>>> sysconfig.get_path('platstdlib')
'/usr/local/lib/python3.11'

Or on a Python build configured with lib64 platlibdir (e.g. on Fedora Linux with $RPM_BUILD_ROOT environment variable set):

>>> import sysconfig
>>> sysconfig.get_path('stdlib')
'/usr/lib64/python3.11'
>>> sysconfig.get_path('platstdlib')
'/usr/lib64/python3.11'

Yet in virtual environments, the platstdlib directory returns a directory from within the virtual environment. E.g. in the python:3.11.1 Docker container:

>>> import sysconfig
>>> sysconfig.get_path('stdlib')
'/usr/local/lib/python3.11'
>>> sysconfig.get_path('platstdlib')
'.../myvenv/lib/python3.11'

Or on Fedora Linux:

>>> import sysconfig
>>> sysconfig.get_path('stdlib')
'/usr/lib64/python3.11'
>>> sysconfig.get_path('platstdlib')
'.../myvenv/lib64/python3.11'

This even confuses the default values on Fedora Linux (without $RPM_BUILD_ROOT environment variable set):

>>> import sysconfig
>>> sysconfig.get_path('stdlib')
'/usr/lib64/python3.11'
>>> sysconfig.get_path('platstdlib')
'/usr/local/lib64/python3.11'

I believe that here:

cpython/Lib/sysconfig.py

Line 30 in 62251c3

'platstdlib': '{platbase}/{platlibdir}/python{py_version_short}',

The {platbase} variable should be replaced with {insatlled_base} or even (currently AFAIK nonexistent) {insatlled_platbase}.

Your environment

• CPython versions tested on: 3.11.1
• Operating system and architecture: Fedora Linux 37 x86_64, python:3.11.1 Docker container.

[FFY00]

From my initial impression, I think your analysis and resolution proposal are correct, though I'd like to look into the historical background before making any changes.

[FFY00]

Okay, after digging through the history of sysconfig and Python packaging in general, I believe this was due to DLLs needing to be copied to the venv on Windows before 3.7.2. This became unnecessary with the introduction of redirector scripts.