Singleton

singleton.py

class Singleton(type):
    """
    Metaclass.
    Only allows the creation of one instance, all other tries return
    the same instance of the first creation.
    
    Use:
    class Test(metaclass=Singleton):
        ...
    
    """
    def __init__(self, *args, **kwargs):
        self.__instance = None
        super().__init__(*args, **kwargs)

    def __call__(self, *args, **kwargs):
        if self.__instance is None:
            self.__instance = super().__call__(*args, **kwargs)
        return self.__instance


if __name__ == "__main__":
    class Test(metaclass=Singleton):
        def __init__(self):
            print("Initializing Test")

    a = Test()
    b = Test()
    c = Test()
    print(a is b)
    print(b is c)