How do I correctly add type-hints to Mixin classes?

Question

Consider the following example. The example is contrived but illustrates the point in a runnable example:

class MultiplicatorMixin:

    def multiply(self, m: in         


        

Answer 1

For reference, mypy recommends to implement mixins through a protocol (https://mypy.readthedocs.io/en/latest/more_types.html#advanced-uses-of-self-types).

It works with mypy >= 750.

from typing_extensions import Protocol


class HasValueProtocol(Protocol):
    @property
    def value(self) -> int: ...


class MultiplicationMixin:

    def multiply(self: HasValueProtocol, m: int) -> int:
        return self.value * m


class AdditionMixin:

    def add(self: HasValueProtocol, b: int) -> int:
        return self.value + b


class MyClass(MultiplicationMixin, AdditionMixin):

    def __init__(self, value: int) -> None:
        self.value = value