setuptools.windows_support requires ctypes support even on non-Windows

[ronaldoussoren]

The module setuptools.windows_support unconditionally imports "ctypes", even though this module is only used when running on a Windows machine. The result of this is that setuptools is unusable on systems without ctypes (in my case because I'm running macOS on arm64 where the patches needed to get ctypes support haven't been merged yet).

Environment Details

• Operating System and version: macOS 11, arm64
• Python version: 3.10 (trunk)
• Python installed how: Manually
• Virtualenv version (if using virtualenv): n/a

Command(s) that triggered the warning/error (and output):

python setup.py install     # for a project using setuptools in its setup.py file 

Command(s) used to install setuptools (and output): Setuptools was installed when building python "make install".

Versions:

% pip list
Package    Version
---------- -------
pip        20.1.1
setuptools 47.1.0

[jaraco]

Thanks for the report. That does sound like an inconvenience.

On one hand, this sounds like a defect lies with Python and will be fixed in Python. Indeed, this issue could be worked around by touch $PYTHON_LIB/ctypes.py.

Given that this issue is only affecting a non-final release and is likely to be fixed before that final release, I'm tempted to say a temporary workaround should be preferable to editing the setuptools source.

What do you think? Should Setuptools adjust for this temporarily degraded state?

[ronaldoussoren]

My particular case is just an inconvenience that I worked around by patching setuptools.

Is ctypes essential enough to have a hard dependency on it regardless of the platform? I'd expect that all major platforms are supported by libffi and hence ctypes, but there may be obscure platforms that run Python without providing ctypes.

The hard dependency can be avoided by moving the import inside setuptools.windows_support.hidden_file.

I don't have a strong opinion either way.

[jaraco]

Is ctypes essential enough to have a hard dependency on it regardless of the platform?

Not really. Surely the import could be made late, and already the import for ctypes.wintypes is tucked inside there as it's the only one until now that was reported as selectively available, but even that behavior is a bug. It seems to me that Python is advertising ctypes as always importable, so my preference would be to rely on that (somewhat implicit) guarantee in order to keep the code as simple and uniform as possible.

If on the other hand, Python were to document that ctypes is only sometimes importable and recommends a technique to avoid errors on select systems, I'd be much more inclined to adopt the recommendation.

[Avasam]

Pretty sure this was fixed by #3178