This snippet showcases how to decorate methods declared in child classes

init_subclass.py

from contextlib import contextmanager


@contextmanager
def show_start_end():
    print('START')
    try:
        yield
    finally:
        print('THE END')


def decorate(function):
    def wrapper(*args, **kwargs):
        with show_start_end():
            return function(*args, **kwargs)
    return wrapper


class Parent:
    def __init_subclass__(cls):
        print('INIT')
        print(cls.some_method)
        super().__init_subclass__()
        print(cls.some_method)
        cls.some_method = decorate(cls.some_method)
        print(cls.some_method)


class Child(Parent):
    def some_method(self):
        return 'some'


print(Child().some_method())