def flyweight(cls):
    instances = dict()
    return lambda *args, **kargs: instances.setdefault(
                                            (args, tuple(kargs.items())),
                                            cls(*args, **kargs))


#----------------------------------------------------------
@flyweight
class Spam(object):
    def __init__(self, a, b):
        self.a = a
        self.b = b


@flyweight
class Egg(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y


assert Spam(1, 2) is Spam(1, 2)
assert Egg('a', 'b') is Egg('a', 'b')
assert Spam(1, 2) is not Egg(1, 2)

# No way to subclass