old_contents: class Game():
      def __init__(self):
          pass
  
      def roll(self, pins):
          pass
  
      def score(self):
          return 0
  
new_contents: class Game():
      def __init__(self):
          self._score = 0
  
      def roll(self, pins):
          pass
  
      def score(self):
          return 0
  
subject: Add score attribute