assert_type with callable seems to require a param name

[Vulwsztyn]

However weird it sounds, pyright seems to expect a name of the parameter in a Callable when using assert_type

For such code:

from typing import assert_type
from collections.abc import Callable
def tuple_of_nums(n: int) -> tuple[int,...]:
    return tuple(range(n))
assert_type(tuple_of_nums, Callable[[int], tuple[int,...]])

running pyright file.py yields:

file.py:5:13 - error: "assert_type" mismatch: expected "(int) -> tuple[int, ...]" but received "(n: int) -> tuple[int, ...]" (reportAssertTypeFailure)

The only difference being n: in the received function.

How do I make this type assert work?

[erictraut]

assert_type tests for type equivalency, not type assignability. The type of tuple_of_nums is (n: int) -> tuple[int, ...]. The type described by the annotation Callable[[int], tuple[int, ...]] is a subtype of this type, but it's not equivalent because it does not accept a keyword argument n.

If you want to test for type assignability, then assert_type isn't the right tool to use. You can instead simply include an assignment, and a type checker will verify assignability.

x: Callable[[int], tuple[int,...]] = tuple_of_nums

[Vulwsztyn]

SO link

https://stackoverflow.com/questions/79437137/assert-type-with-callable