old_contents: class Pair:
      def __init__(self, question, answer):
          self.question = question
          self.answer = answer
  
      def __iter__(self):
          return iter({'question': self.question, 'answer': self.answer}.items())
  
new_contents: class Pair:
      def __init__(self, _id, question, answer):
          self.id = _id
          self.question = question
          self.answer = answer
  
      def __iter__(self):
          return iter({'id': self.id, 'question': self.question, 'answer': self.answer}.items())
  
subject: Add id to Pair