main.py

class MetaSingleton(type):

    _instances = {}

    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            cls._instances[cls] = super(MetaSingleton, cls).__call__(
                *args, **kwargs
            )
        return cls._instances[cls]


class Logger(metaclass=MetaSingleton):
    def __init__(self, x):
        self.x = x


class Singleton1:

    __instance = None

    def __new__(cls, nome):
        if Singleton1.__instance is None:
            Singleton1.__instance = object.__new__(cls)
            Singleton1.__instance.__nome = nome
        return Singleton1.__instance

    @property
    def nome(self):
        return self.__nome


class Singleton2:
    def __new__(cls, nome):
        if not hasattr(cls, 'instance'):
            cls.instance = super(Singleton2, cls).__new__(cls)
            cls.instance.__nome = nome
        return cls.instance

    @property
    def nome(self):
        return self.__nome


if __name__ == '__main__':

    foo = Singleton1('Maria')
    print(foo.nome)
    print(foo)

    bar = Singleton1('Joao')
    print(bar.nome)
    print(bar)

    print(foo is bar)

    foo = Singleton2('Maria')
    print(foo.nome)
    print(foo)

    bar = Singleton2('Joao')
    print(bar.nome)
    print(bar)

    print(foo is bar)

    # Example using metaclass
    logger1 = Logger(1)
    logger2 = Logger(2)

    print(logger1)
    print(logger1.x)
    print(logger2)
    print(logger2.x)