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