old_contents: # Hello World
  
  import sys
  
  
  def hello(thing):
      print "Hello {}".format(thing)
      return
  
  
  if __name__ == "__main__":
      sys.exit(hello())
  
new_contents: # Hello World
  
  import sys
  
  
  def hello(thing):
      print "Hello {}".format(thing)
      return
  
  
  if __name__ == "__main__":
      user_thing = sys.argv[-1]
      sys.exit(hello(user_thing))
  
subject: Allow user to specify thing.