Return type in mypy with typevars annotated args

[adam-urbanczyk]

Any clue how difficult it would be to fix the mypy reported return type in the case of TypeVar annotations? See this link for more details (or the example below): https://github.com/CadQuery/cadquery/issues/379#issuecomment-830873519

from typing import TypeVar
from multimethod import multimethod

T0 = TypeVar('T0', bound='Shape')
T1 = TypeVar('T1', bound='MMShape')

class Shape:
    def set_scale(self: T0, scale: float) -> T0:
        self.scale = scale
        return self

class MMShape:
    @multimethod
    def set_scale(self: T1, scale: float) -> T1:
        self.scale = scale
        return self

s0 = Shape().set_scale(1.0)
reveal_type(s0)

s1 = MMShape().set_scale(1.0)
reveal_type(s1)

> mypy chain_test.py
chain_test.py:22: note: Revealed type is 'chain_test.Shape'
chain_test.py:25: note: Revealed type is 'Any'

[coady]

Yes, that was contributed recently actually: #37. Already works for functions, and just needs to annotate __get__ to support methods.

It's implemented on multidispatch only, because it (like singledispatch) requires a base implementation.

[adam-urbanczyk]

Thanks!