Shared via mypy Playground

main.py

from typing import *

class B():
    def f(self) -> Self:
        return self
        
class C(B):
    pass
class D(B):
    pass


T = TypeVar(
    "T",
    C,
    D,
)

def g(
    b: T,
) -> T:
    return b.f()

TBounded = TypeVar(
    "TBounded",
    bound=B
)

def g_bounded(
    b: TBounded,
) -> TBounded:
    return b.f()