[whilenot-dev]

The abstraction gets leaky once you expect the distinct NewTypes to adhere to the original inheritance property. I think that's a wrong assumption from the get-go.

OP could just do:

    def foo(val: _A) -> None:
        pass

...and it'll accept both NewTypes just fine. I guess it depends on whether foo is designed to be public or private.

[sdeframond]

This works but it does not let other modules define such methods.