old_contents: class Person:
      def __init__(self, name, birthdate):
          self.name = name
          self.birthdate = birthdate
  
  
  class Birthdate:
      def __init__(self, year, day):
          self.year = year
          self.day = day
  
  
  class Day:
      def __init__(self, day, month):
          self.day = day
          self.month = month
  
new_contents: class Person:
      def __init__(self, name, birth_date):
          self.name = name
          self.birth_date = birth_date
  
  
  class BirthDate:
      def __init__(self, year, date):
          self.year = year
          self.date = date
  
  
  class Date:
      def __init__(self, day, month):
          self.day = day
          self.month = month
  
      def write_into(self, list):
          list.append(self)
  
subject: Rename class and attribute