import abc


class Singleton(abc.ABC):
    """ source: https://www.python.org/download/releases/2.2/descrintro/#__new__ """
    def __new__(cls, *args, **kwds):
        it = cls.__dict__.get("__it__")
        if it is not None:
            return it

        cls.__it__ = it = super(Singleton, cls).__new__(cls)
        it.init(*args, **kwds)
        return it

    @abc.abstractmethod
    def init(self, *args, **kwds):
        pass



if __name__ == '__main__':

    class Test(Singleton):
        def init(self):
            print("Calling init")


    print(id(Test()))
    print(id(Test()))