new_contents: from tornado.web import RequestHandler
  from torndsession.session import SessionMixin
  
  class BaseRequestHandler(RequestHandler, SessionMixin):
      """
      BaseRequestHandler should be used on any app class
      handler thant want to implement tornado RequestHandler
      and by default mixed with torndsession.session.SessionMixin
      to manage all session things.
      """
  
      def prepare(self):
          pass
  
      def on_finish(self):
          """
          Every request finished, torndsession will
          save session contents.
          """
          self.session.flush()
  
subject: Create base request handler, mixed with session handler