metaflyweight = lambda name, parents, attrs: type(
        name,
        parents,
        dict(attrs.items() + [
            ('__instances', dict()),
            ('__new__', classmethod(
                lambda cls, *args, **kargs: cls.__instances.setdefault(
                                tuple(args),
                                super(type(cls), cls).__new__(*args, **kargs))
                )
            )
        ])
    )


#----------------------------------------------------------
class Spam(object):
    __metaclass__ = metaflyweight

    def __init__(self, a, b):
        self.a = a
        self.b = b


class Egg(object):
    __metaclass__ = metaflyweight

    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
class SubSpam(Spam):
    pass

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