old_contents: class Entity(object):
      pass
  
  class Player(Entity):
      pass
  
  class NPC(Entity):
      pass
  
new_contents: class EntityType(object):
      NUM_DEFAULT_TYPES = 3
      All, Player, Enemy = range(NUM_DEFAULT_TYPES)
  
  class Entity(object):
      pass
  
  class Player(Entity):
      pass
  
  class NPC(Entity):
      pass
  
subject: add EntityType