Shared via mypy Playground

main.py

import typing as t


def fails(
    foo: int | None = None,
    bar: int | None = None,
) -> None:
    default = 1337
    match (foo, bar):
        case (None, None):
            foo = default
            bar = default
        case (None, val):
            foo = val
        case (val, None):
            bar = val
        case (_, _):
            pass
        case _:
            # It would be great to be able to use `assert` here, but somehow
            # mypy does not recognise that the match statement is exhaustive.
            t.assert_never(foo)


def fails_too(
    foo: int | None = None,
    bar: int | None = None,
) -> None:
    default = 1337
    match foo, bar:
        case None, None:
            foo = default
            bar = default
        case None, val:
            foo = val
        case val, None:
            bar = val
        case _, _:
            pass
        case _:
            # It would be great to be able to use `assert` here, but somehow
            # mypy does not recognise that the match statement is exhaustive.
            t.assert_never(foo)


def fails_1tuple(
    foo: int | None = None,
) -> None:
    default = 1337
    match (foo,):
        case (None,):
            foo = default
        case (_,):
            pass
        case _:
            # It would be great to be able to use `assert` here, but somehow
            # mypy does not recognise that the match statement is exhaustive.
            t.assert_never(foo)


def works(
    foo: int | None = None,
) -> None:
    default = 1337
    match foo:
        case None:
            foo = default
        case _val:
            pass
        case _:
            t.assert_never(foo)