Python protocol inheritance

protocol-inheritance.py

from typing import Protocol


class IFoo(Protocol):
    def bar(self) -> None:
        ...


class BaseFoo:
    def bar(self) -> None:
        print('base foo', type(self))


class Foo(IFoo):
    pass


class ChildFooA(BaseFoo, IFoo):
    pass


class ChildFooB(IFoo, BaseFoo):
    pass


Foo().bar()  # mypy(error): Cannot instantiate abstract class "Foo" with abstract attribute "bar"  [abstract]
# does not print

BaseFoo().bar()
# prints: base foo <class '__main__.BaseFoo'>

ChildFooA().bar()
# prints: base foo <class '__main__.ChildFooA'>

ChildFooB().bar()  # mypy(error): Cannot instantiate abstract class "ChildFooB" with abstract attribute "bar"  [abstract]
# does not print