oop-solid-design-patterns/problem5_observer.py at main · khadijafatima409/oop-solid-design-patterns · GitHub

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"""
Problem 5: Observer Pattern
"""

from abc import ABC, abstractmethod


class Observer(ABC):
    @abstractmethod
    def update(self, news): pass


class Subject(ABC):
    @abstractmethod
    def attach(self, observer): pass

    @abstractmethod
    def detach(self, observer): pass

    @abstractmethod
    def notify(self): pass


class NewsPublisher(Subject):
    def __init__(self):
        self.observers = []
        self.news = None

    def attach(self, observer):
        self.observers.append(observer)

    def detach(self, observer):
        self.observers.remove(observer)

    def notify(self):
        for observer in self.observers:
            observer.update(self.news)

    def publish_news(self, news):
        self.news = news
        self.notify()


class EmailSubscriber(Observer):
    def update(self, news):
        print("Email received:", news)


class SMSSubscriber(Observer):
    def update(self, news):
        print("SMS received:", news)


class AppSubscriber(Observer):
    def update(self, news):
        print("App notification:", news)


if __name__ == "__main__":
    publisher = NewsPublisher()

    email = EmailSubscriber()
    sms = SMSSubscriber()
    app = AppSubscriber()

    publisher.attach(email)
    publisher.attach(sms)
    publisher.attach(app)

    publisher.publish_news("Breaking News!")

    publisher.detach(sms)
    publisher.publish_news("Second News!")