class Thingy(object):

    def __len__(self):
        return 10
lengthy_thingy = Thingy()
lengthy_thingy.__len__ = lambda self: 20
print(len(lengthy_thingy))
print(lengthy_thingy.__len__(lengthy_thingy))
print(type(lengthy_thingy).__len__(lengthy_thingy))
Семантический эквивалент async для