Python type hint for (any) class

Question

I’d recommend using a combination of TypeVar, to indicate that your self.o value could be any arbitrary type, and Type, in the following way:

from typing import TypeVar, Type

T = TypeVar('T')

class MyObj:
    def __init__(self, o: T) -> None:
        self.o = o

    def get_obj_class(self) -> Type[T]:
        return type(self.o)

def accept_int_class(x: Type[int]) -> None:
    pass

i = MyObj(3)
foo = i.get_obj_class()
accept_int_class(foo)    # Passes

s = MyObj("foo")
bar = s.get_obj_class()
accept_int_class(bar)    # Fails

If you want the type of o to be even more dynamic, you could explicitly or implicitly give it a type of Any.

Regarding your latter question, you’d do:

def f(cls: Type[T]) -> T:
    return cls()

Note that you need to be careful when instantiating your class — I don’t remember what Pycharm does here, but I do know that mypy currently does not check to make sure you’re calling your __init__ function correctly/with the right number of params.

(This is because T could be anything, but there’s no way to hint what the constructor ought to look like, so performing this check would end up being either impossibly or highly difficult.)

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