old_contents: class TDatabase(object):
      db_host = '127.0.0.1'
      db_port = 3306
      db_username = None
      db_password = None
      db_database = None
      db_charset = 'utf8'
      db_autocommit = True
  
  
  class UserDB(TDatabase):
      DB_PORT = 3307
  
  
  if __name__ == '__main__':
      a = UserDB()
      a.db_port = 10
      print(a.db_port)
  
new_contents: class TDatabase(object):
      db_host = '127.0.0.1'
      db_port = 3306
      db_username = None
      db_password = None
      db_database = None
      db_charset = 'utf8'
      db_autocommit = True
  
subject: add TDatabase.