[Python] How to write type hints for a function returning itself?

from typing import Callable


def f() -> Callable:
return f


How to explicitly define f's type? like Callable[[], Callable]

I think it is slightly like a linked list, but I can't implement it.

from typing import Union


class Node:
def __init__(self, val):
self.val = val
self.next: Union[Node, None] = None

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