text: import json
  
  from django.conf import settings
  from django.contrib.messages.storage.base import BaseStorage
  from django.contrib.messages.storage.cookie import (
      MessageDecoder, MessageEncoder,
  )
  
  
  class SessionStorage(BaseStorage):
      """
      Stores messages in the session (that is, django.contrib.sessions).
      """
      session_key = '_messages'
  
      def __init__(self, request, *args, **kwargs):
          assert hasattr(request, 'session'), "The session-based temporary "\
              "message storage requires session middleware to be installed, "\
              "and come before the message middleware in the "\
              "MIDDLEWARE%s list." % ("_CLASSES" if settings.MIDDLEWARE is None else "")
          super(SessionStorage, self).__init__(request, *args, **kwargs)
  
      def _get(self, *args, **kwargs):
          """
          Retrieves a list of messages from the request's session.  This storage
          always stores everything it is given, so return True for the
          all_retrieved flag.
          """
          return self.deserialize_messages(self.request.session.get(self.session_key)), True
  
      def _store(self, messages, response, *args, **kwargs):
          """
          Stores a list of messages to the request's session.
          """
          if messages:
              self.request.session[self.session_key] = self.serialize_messages(messages)
          else:
              self.request.session.pop(self.session_key, None)
          return []
  
      def serialize_messages(self, messages):
          encoder = MessageEncoder(separators=(',', ':'))
          return encoder.encode(messages)
  
      def deserialize_messages(self, data):
          if data and isinstance(data, str):
              return json.loads(data, cls=MessageDecoder)
          return data
  