gh-138614: site._get_path to respect non-default implementation name

[ShaharNaveh]

fix #138614

• Issue: site.py hardcodes "python" instead of using {implementation_lower} #138614

[bedevere-app]

Most changes to Python require a NEWS entry. Add one using the blurb_it web app or the blurb command-line tool.

If this change has little impact on Python users, wait for a maintainer to apply the skip news label instead.

[picnixz]

• When is it an issue?
• Please open an issue first to discuss the rationale.

[bedevere-app]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[picnixz]

Please add a NEWS entry, something like:

:mod:`site`: correctly synchronize the ``purelib`` installation
scheme with the one defined in :mod:`sysconfig`.

Issue is real.

[picnixz]

After some thoughts, what I wrote is a bit too obscure. Let's mention the public API:

Suggested change

	:mod:`site`: correctly synchronize the ``purelib`` installation scheme with
	the one defined in :mod:`sysconfig`.
	:mod:`site`: correctly synchronize the ``purelib`` installation scheme with
	the one defined in :mod:`sysconfig`. This affects the default user-specific
	site-packages directory path (see :func:`site.getusersitepackages`).

[picnixz]

Following the maintainer's feedback, you can remove the NEWS entry.

[FFY00]

Do we have any actual user-facing downstream issues? If so, we can keep the NEWS entry (with @picnixz's proposed change), otherwise I think we should just drop it.

cc @ShaharNaveh

[picnixz]

We also need to update https://docs.python.org/3/library/site.html#site.USER_SITE:

Path to the user site-packages for the running Python. Can be None if getusersitepackages() hasn’t been called yet. Default value is ~/.local/lib/pythonX.Y[t]/site-packages for UNIX and non-framework macOS builds, ~/Library/Python/X.Y/lib/python/site-packages for macOS framework builds, and %APPDATA%\Python\PythonXY\site-packages on Windows. The optional “t” indicates the free-threaded build. This directory is a site directory, which means that .pth files in it will be processed.

It shouldn't be "Python" but whatever implementation it is being used.

[picnixz]

Strictly speaking, _get_implementation is hard-coded and private so it shouldn't be modifiable by end-users. Does PyPy do something here? if it's only meant to be used internally, we may not need to update the docs for now.

We do have an issue of synchronization that I'm ok to fix, but it won't be visible to end-users so we may just forget about NEWS entries. I'll wait for @FFY00 feedback.

[FFY00]

Strictly speaking, _get_implementation is hard-coded and private so it shouldn't be modifiable by end-users. Does PyPy do something here? if it's only meant to be used internally, we may not need to update the docs for now.

Yes, it is meant to be patched by other implementations, to minimize the amount patching required in the rest of the code, and help keep everything in sync.

We do have an issue of synchronization that I'm ok to fix, but it won't be visible to end-users so we may just forget about NEWS entries. I'll wait for @FFY00 feedback.

I don't think we need a NEWS entry.

[FFY00]

@ShaharNaveh, thanks for working on this!

[ShaharNaveh]

I don't think we need a NEWS entry.

Alright, will fix the PR in a bit