Shared via mypy Playground

main.py

from typing import TypeVar, Literal

A = TypeVar("A")
B = TypeVar("B")

MutExResult = tuple[Literal["neither"], None, None] | tuple[Literal["both"], A, B] | tuple[Literal["left"], A, None] | tuple[Literal["right"], None, B]


def check_mutually_exclusive(a: A | None, b: B | None) -> MutExResult[A, B]:
    if a is None and b is None:
        return "neither", None, None
    elif a is not None and b is not None:
        return "both", a, b
    elif a is not None:
        return "left", a, None
    else:
        assert b is not None
        return "right", None, b
        
        
def usage(a1: int | None, b1: str | None):
    
    res, a, b = check_mutually_exclusive(a1, b1)
    reveal_type(res)
    reveal_type(a)
    reveal_type(b)
    
    if res == "both":
        reveal_type(a)
        reveal_type(b)
    elif res == "neither":
        reveal_type(a)
        reveal_type(b)
    elif res == "left":
        reveal_type(a)
        reveal_type(b)
    elif res == "right":
        reveal_type(a)
        reveal_type(b)


def usage2(a1: int | None, b1: str | None):
    
    res = check_mutually_exclusive(a1, b1)
    reveal_type(res)

    if res[0] == "both":
        reveal_type(res[1])
        reveal_type(res[2])
    elif res[0] == "neither":
        reveal_type(res[1])
        reveal_type(res[2])
    elif res[0] == "left":
        reveal_type(res[1])
        reveal_type(res[2])
    elif res[0] == "right":
        reveal_type(res[1])
        reveal_type(res[2])