The child class does not call code of the parent class

The child class does not call code of the parent class.
I wrote this code. I thought the Id field of the Extension2 class would be 2, but it is 1

myvariable = 0
lock = threading.Lock()


def get_next_id() -> int:
    global myvariable
    global lock
    with lock:
        myvariable += 1
        return myvariable


class Extension:
    Id = get_next_id()


class Extension2(Extension):
    pass

>Solution :

Defining Id in the parent class only defines it once. Children inherit this value, but the expression isn’t re-evaluated. You can use __init_subclass__ to force evaluation on every subclass, sort of like __init__ does for instances.

class Extension:
    Id = get_next_id()

    @classmethod
    def __init_subclass__(cls):
        cls.Id = get_next_id()

Try it online!