python multimethod pattern

multimethod.py

# def collide(thing1, thing2):
#     if thing1.is_asteroid() and thing2.is_spaceship():
#         thing2.destroy()
#     elif thing1.is_spaceship() and thing2.is_asteroid():
#         thing1.destroy()
#     elif thing1.is_spaceship() and thing2.is_spaceship():
#         random.choice([thing1, thing2]).desmaterialize()
#     elif thing1.is_asteroid() and thing2.is_asteroid():
#         universe.boom()
# structured approach


class dispatcher(dict):
    add_rule = lambda self, things, fn: self.__setitem__(things, fn)
    execute = lambda self, things: self[things](things)

collide = dispatcher()
collide.add_rule((Asteroid, Spaceship), destroy_spaceship)
collide.add_rule((Spaceship, Spaceship), destroy_spaceship)
collide.add_rule((Asteroid, Asteroid), boom)