class flyweight(object):
    def __init__(self, cls):
        self._cls = cls
        self._instances = dict()

    def __call__(self, *args, **kargs):
        return self._instances.setdefault(
                                    (args, tuple(kargs.items())),
                                    self._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)

# Subclassing a flyweight class
@flyweight
class SubSpam(Spam._cls):
    pass

assert SubSpam(1,2) is SubSpam(1,2)
assert Spam(1,2) is not SubSpam(1,2)