import weakref

class Cached(type):
def init(self, *args, *kwargs):
super().init(args, **kwargs)
self.__cache = weakref.WeakValueDictionary()

def __call__(self, *args):
    if args in self.__cache:
        return self.__cache[args]
    else:
        obj = super().__call__(*args)
        self.__cache[args] = obj
        return obj

Example

class Spam(metaclass=Cached):
def init(self, name):
print('Creating Spam({!r})'.format(name))
self.name = name

调用

a = Spam('Guido')
Creating Spam('Guido')
b = Spam('Diana')
Creating Spam('Diana')
c = Spam('Guido') # Cached
a is b
False
a is c # Cached value returned
True