Observer Design Pattern Template

observer_design.py

# Observer Design Pattern is mainly used in scenarios when there is a change in the Class attributes
# which should be reflected to all of its objects. This technique is explained with the help of Podcast 
# example. Here whenever new podcast is uploaded, it should notify all the subscribers.

class Podcast(object):
    def __init__(self,subscriber_name):
        self.subscriber_name = subscriber_name
    def get_podcast(self):
        return self._podcasts
    def add_podcast(self,podcast_name):
        self._podcasts.add(podcast_name)
    def delete_podcast(self,podcast_name):
        self._podcasts.remove(podcast_name)
        
    # This where we actually implement the observer desing pattern logic
    # We create a set called _podcasts which contains all the podcast that
    # has been uploaded and its acts a global object to all instance of
    # this class
    def __new__(cls):
        if not hasattr(cls,'_podcasts'):
            cls._podcasts = set()
        return super(Podcast,cls).__new__(cls)
    
def __name__ == '__main__':
    # Creating three users (Admin and two subscribers)
    admin = Podcast('admin')
    kishore = Podcast('kishore')
    devaraj = Podcast('devaraj')
    
    # Now the admin adds few podcasts to the Podcast Class
    admin.add_podcast("Bitcoin and its future")
    admin.add_podcast("Writing Idomatic Python")
    
    # Now each client who has subscribed to that podcast we receive 
    # these podcasts in the respective object instances.
    kishore.get_podcast()
    # {'Bitcoin and its future','Writing Idomatic Python'}
    devaraj.get_podcast()
    # {'Bitcoin and its future','Writing Idomatic Python'}
    
    # Similarly whenever the admin delete a existing a podcast
    # it will be deleted from all the instances.