Cache supported tags for wheels.

[mauritsvanrees]

Summary of changes

In wheel.py:Wheel.is_compatible we called sys_tags each time to get the list of supported tags. Now we call this once, and cache the result in a simple variable. This drastically speeds up checking the compatibility of hundreds of wheels.

Closes #3804

Pull Request Checklist

• Changes have tests
• News fragment added in changelog.d/.
  (See documentation for details)

[abravalheri]

Hi @mauritsvanrees, thank you for the contribution and sorry for delay in reviewing...

I noticed that you used a global var for the implementation and some patching/mocking/stubbing capabilities for the tests.

What do you think about functools.lru_cache(maxsize=None)? (I think functools.cache would be better, but it is not available before 3.9 - and by looking at the implementation they are equivalent).

It seems also more elegant for testing because you can call clear_cache and there seems to be some evidence that it is faster because it is written in C.

---

Small note:

I don't know if setuptools/wheel.py is going to be maintained for long after we completely remove install/easy_install, but I understand that this is going to be a different discussion, which should involve the Buildout team that heavily uses it.

Since I could not find any references in the docs about it being deprecated, my assumption is that it is OK to add non-disruptive improvements.

[mauritsvanrees]

Hi @abravalheri. Thanks for the review and sorry for the delay in acting on it.

What do you think about functools.lru_cache(maxsize=None)?

Good point. I should probably use that function more often.
I have added a commit to do this. (And rebased on main and force pushed.)

This change has no effect on the timing of my small test script in issue #3804: the significant performance increase remains.

[mauritsvanrees]

Thanks for your support @abravalheri!