bpo-37540: vectorcall: keyword names must be strings

[jdemeyer]

The fact that keyword names are strings is now part of the vectorcall and METH_FASTCALL protocols. The biggest concrete change is that _PyStack_UnpackDict now checks that and raises TypeError if not.

CC @markshannon@vstinner

https://bugs.python.org/issue37540

Automerge-Triggered-By: @encukou

[encukou]

Instead of "string", I'd say "`str` or a subclass" explicitly.
(In documentation; not necessarily in error messages)

[jdemeyer]

There are many instances in the documentation (unrelated to vectorcall) where the word "string" is used. I don't see the problem here.

Concrete proposal: we leave this doc as is and I will reboot #13844 (I always planned to do that, but after all other PRs that affect documentation). In the section describing the "vectorcall protocol", I will say explicitly what "string" means for vectorcall.

[jdemeyer]

Is this PR okay now or do you want me to change things?

[encukou]

@markshannon, you said you were looking at this PR. Is that still the case? Any progress?

[jdemeyer]

Ping?

[encukou]

@markshannon seems unresponsive. I don't see an issue with this PR.

[encukou]

I see f(**{1:2}) is still tested in test_excall.py.

[jdemeyer]

Indeed. This is testing two errors at the same time (duplicate keyword and non-string keyword). Which of the two errors you get seems arbitrary to me and this PR changes the error.

[jdemeyer]

Thanks! This will help to make progress on some other PRs.