Cached

cached.py

import weakref


class Cached(type):
    """
    Metaclass.
    Only allows the creation of one type of instance, all other instances
    with the same initialization variables return the same instance of the
    first creation.
    
    Use:
    class Test(metaclass=Cached):
        ...
    """

    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


if __name__ == "__main__":

    class Test(metaclass=Cached):
        def __init__(self, name):
            self.name = name
            print(f"Initializing Test({name})")

    a = Test("A")
    b = Test("B")
    c = Test("A")  # Cached
    print(a is b)
    print(a is c)  # Cached value returned