Shared via mypy Playground

main.py

from pathlib import Path


class MyClass:
    def __init__(self, path: Path | None) -> None:
        self.path = path


def test(a: MyClass, b: MyClass):
    if a.path is None:
        raise ValueError(f"a.path cannot be None")
    if b.path is None:
        raise ValueError(f"b.path cannot be None")

    # This line will cause an error for the line "b.path.exists()": error: Item "None" of "Path | None" has no attribute "exists"  [union-attr]
    b = a

    if a.path.exists():
        print("a path exist")

    if b.path.exists():
        print("b path exist")


def main():
    a = MyClass(Path("."))
    b = MyClass(Path("."))

    test(a, b)


if __name__ == "__main__":
    main()