False negative with ParamSpec

[hauntsaninja]

On mypy master, this does not have any errors:

from typing import Callable, ParamSpec

P = ParamSpec('P')

def twice(f: Callable[P, int], *args: P.args) -> int:
  return f(*args) + f(*args)

With 0.982 you get main.py:5: error: Name "P.args" is not defined. Not the best error message, but at least you get an error for invalid use.

This bisects to https://github.com/python/mypy/pull/13472/files cc @sobolevn

[sobolevn]

Fixed! Sending a PR.

[nickeldan]

Perhaps I'm missing something but what is the error? Isn't that the correct usage of P.args?

[AlexWaygood]

Perhaps I'm missing something but what is the error? Isn't that the correct usage of P.args?

It's invalid to use only P.args in a function. You have to use P.args and P.kwargs, or neither. This is specified in PEP 612 (https://peps.python.org/pep-0612/#id1), but isn't currently mentioned in the typing.py docs (maybe it should be).

[nickeldan]

It's invalid to use only P.args in a function. You have to use P.args and P.kwargs, or neither. This is specified in PEP 612 (https://peps.python.org/pep-0612/#id1), but isn't currently mentioned in the typing.py docs (it probably should be).

Ah, thanks!

[sobolevn]

@AlexWaygood would you care to create an issue about that?

[AlexWaygood]

@AlexWaygood would you care to create an issue about that?

About the CPython docs?

[sobolevn]

Yes, about:

It's invalid to use only P.args in a function. You have to use P.args and P.kwargs, or neither. This is specified in PEP 612 (https://peps.python.org/pep-0612/#id1), but isn't currently mentioned in the typing.py docs (maybe it should be).