Fixes for python3.10

[asottile]

Summary of changes

found using asottile/python3.10

Pull Request Checklist

• Changes have tests -- 17 tests failed prior to this change
• News fragment added in changelog.d. See documentation for details

[asottile]

@pganssle would appreciate a review <3

[pganssle]

I think it might be good to pull this from a centralized place rather than repeating the same formatting idiom in a bunch of places.

[asottile]

sounds good -- do you have a recommended place to put this little helper "constant"?

[asottile]

@pganssle ping! should I put these in some sort of _compat module?

[pganssle]

@asottile I dunno if _compat is right, it's more like _environment or _platform or something.

The one in setup.py can stay as it is, though.

@jaraco Do you have any suggestions, code-organization-wise?

[jaraco]

Honestly, I struggle with a good place to put this logic, because the usage appears in

• setuptools/* (4)
• pkg_resources/* (including doctests) (3)
• setup.py (1)

There's just no good place to this indication. Here's what I suggest - let's wait for this idiom (or the resulting value) to appear in packaging (on which both pkg_resources and setuptools both depend) and then rely on it from there (except maybe for setup.py).

And in the meantime, let's accept it as proposed.