Unbound ParamSpec, but why?

[hannes-ucsc]

https://mypy-play.net/?gist=be5f1112a53340852f64b306529e0f3f

from typing import Callable

def params[R, **P](*args: P.args, **kwargs: P.kwargs) -> Callable[[Callable[P, R]], R]:
    """
    Returns a function that calls its sole argument with the given parameters.

    >>> from operator import add, sub

    >>> params(1, 2)(add)
    3

    Useful for mapping over an iterable of functions

    >>> list(map(params(1, 2), [add, sub]))
    [3, -1]
    """
    return lambda f: f(*args, **kwargs)

yields

main.py:3: error: ParamSpec "P" is unbound  [valid-type]
Found 1 error in 1 file (checked 1 source file)

… and I don't understand why. This seem like an archetypal use of ParamSpec.

[randolf-scholz]

It's often worth it to test more than one type-checker (for example with https://github.com/astral-sh/multiplay). ty, zuban, pyright and pyrefly all report no errors on this example. I'd say this looks like a mypy bug.