text: #!usr/bin/env python3
  # -*- coding: utf-8 -*-
  
  """
  Application that actually uses Observer Pattern.
  """
  
  __author__ = 'Ziang Lu'
  
  from observer import Follower
  from subject import Tweeter
  
  
  def main():
      trump = Tweeter('Donald Trump')
      american1 = Follower('US Citizen 1')
      american2 = Follower('US Citizen 2')
      american1.follow(trump)
      american2.follow(trump)
  
      print()
      trump.write_tweet('A wonderful day with my family!')
  
      print()
      american1.unfollow(trump)
      american2.unfollow(trump)
  
  
  if __name__ == '__main__':
      main()
  
  # Output:
  # US Citizen 1: Starting to follow Donald Trump
  # US Citizen 2: Starting to follow Donald Trump
  #
  # Donald Trump: I wrote a new tweet: A wonderful day with my family!
  # US Citizen 2: I got an update from Donald Trump about a new tweet: A wonderful day with my family!
  # US Citizen 1: I got an update from Donald Trump about a new tweet: A wonderful day with my family!
  #
  # US Citizen 1: Stops to follow Donald Trump
  # US Citizen 2: Stops to follow Donald Trump
  