old_contents: class Player:
  	def __init__(self, name, skill, position):
  		self.name = name
  		self.skill = skill
  		self.position = position
  		
  
new_contents: class Player:
  	def __init__(self, name, skill, position, fitness):
  		self.name = name
  		self.skill = skill
  		self.position = position
  		self.fitness = fitness
  		
  
subject: Update player.py