real.py

from abc import ABCMeta, abstractmethod


class NewsPublisher:
    def __init__(self):
        self.__subscribers = []
        self.__latestNews = None

    def attach(self, subscriber):
        self.__subscribers.append(subscriber)

    def detach(self):
        return self.__subscribers.pop()

    def subscriber(self):
        return [type(x).__name__ for x in self.__subscribers]

    def notifySubscribers(self):
        for sub in self.__subscribers:
            sub.listen()

    def addNews(self, news):
        self.__latestNews = news
        self.notifySubscribers()

    def getNews(self):
        return "Got News:", self.__latestNews


class Subscriber(metaclass=ABCMeta):
    @abstractmethod
    def listen(self):
        pass


class SMSSubscriber(Subscriber):
    def __init__(self, publisher):
        self.publisher = publisher
        self.publisher.attach(self)

    def listen(self):
        print(type(self).__name__, self.publisher.getNews())


class EmailSubscriber(Subscriber):
    def __init__(self, publisher):
        self.publisher = publisher
        self.publisher.attach(self)

    def listen(self):
        print(type(self).__name__, self.publisher.getNews())


class AnyOtherSubscriber(Subscriber):
    def __init__(self, publisher):
        self.publisher = publisher
        self.publisher.attach(self)

    def listen(self):
        print(type(self).__name__, self.publisher.getNews())


if __name__ == '__main__':
    news_publisher = NewsPublisher()

    for Subscribers in [SMSSubscriber, EmailSubscriber, AnyOtherSubscriber]:
        Subscribers(news_publisher)
    print("\nSubscribers:", news_publisher.subscriber())

    news_publisher.addNews('Hello World!')

    print("\nDetached:", type(news_publisher.detach()).__name__)
    print("\nSubscribers:", news_publisher.subscriber())

    news_publisher.addNews('My second news!')