I'm sure this is already filed somewhere, but I couldn't find anything.

Currently when installing packages with pip using a 64bit Python to --user and then starting a 32bit Python things fail because they look up packages from the same location:

.\python.exe -m site --user-base
C:\Users\user\AppData\Roaming\Python

For example trying to import numpy from a 32bit Python when it was installed with 64bit:

>>> import numpy
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\user\AppData\Roaming\Python\Python39\site-packages\numpy\__init__.py", line 143, in <module>
    from . import _distributor_init
  File "C:\Users\user\AppData\Roaming\Python\Python39\site-packages\numpy\_distributor_init.py", line 26, in <module>
    WinDLL(os.path.abspath(filename))
  File "C:\Python39-32\lib\ctypes\__init__.py", line 374, in __init__
    self._handle = _dlopen(self._name, mode)
OSError: [WinError 193] %1 is not a valid Win32 application

I guess this isn't a very common problem, but in MSYS2 we are facing this issue because users can easily switch between 32bit/64bit Python. We could patch things, but I'm wondering if there are any plans to fix this in CPython itself so we don't invent our own thing.

thanks

The conflict between 32-bit and 64-bit user site-packages was resolved in issue 41627, starting with Python 3.10. It's not practical to backport this change to existing 3.9 installations. 

The "nt_user" install scheme was changed to use the config variable "py_version_nodot_plat". For example:

    >>> sysconfig.get_path('purelib', 'nt_user', expand=False)
    '{userbase}/Python{py_version_nodot_plat}/site-packages'

This variable is based on sys.winver (i.e. the version number of the Python DLL), which includes a "-32" suffix in 32-bit Python. For example:

    >>> sys.winver
    '3.10-32'
    >>> sysconfig.get_config_var('py_version_nodot_plat')
    '310-32'

Ah, wonderful. We'll do something similar then.

Thanks for the info and the pointer to the resolved issue. Much appreciated!