[FIXED] TypeVar in a nested type specification

Issue

Let's say I have a type defined with TypeVar, like so:

T = TypeVar('T')
MyType = Union[list[T], tuple[T]]


def func(a: MyType[int]):
    pass

I also want to have an optional version of it:

MyTypeOpt = Optional[MyType]

def opt_func(a: MyTypeOpt[int] = None):
    pass

But this is not to mypy's liking and I'm getting an error: Bad number of arguments for type alias, expected: 0, given: 1 [type-arg].

Is there a way to make it work without writing Optional[MyType[...]] every time?

Solution

I think you are missing the type parameter for your generic type MyType. mypy is also complaining about that.

from typing import Optional, Sequence, Tuple, Union

from typing_extensions import TypeVar

T = TypeVar('T')
MyType = Union[Sequence[T], Tuple[T]]
MyTypeOpt = Optional[MyType[T]]  # <---------


def func(a: MyType[int]) -> None:
    pass


def opt_func(a: MyTypeOpt[int] = None) -> None:
    pass


def opt_func2(a: Optional[MyType[int]] = None) -> None:
    pass

Answered By - anit3res