Message backend which spits out dictionaries able to be json encoded/decoded, for those session backends which do not pickle.

json_session_messages.py

from django.contrib.messages.storage.base import Message, BaseStorage

class JSONSessionStorage(BaseStorage):
    """
    Stores messages in JSON-compatible format
    """
    session_key = '_messages'
    
    def _to_dict(self, message):
        return {
            'level': message.level,
            'message': message.message,
            'extra_tags': message.extra_tags,
        }
    
    def _from_dict(self, message):
        return Message(**message)
    
    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_CLASSES list."
        super(JSONSessionStorage, 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.
        """
        messages = self.request.session.get(self.session_key)
        messages = map(self._from_dict, messages or [])
        return messages, True
    
    def _store(self, messages, response, *args, **kwargs):
        """
        Stores a list of messages to the request's session.
        """
        if messages:
            messages = map(self._to_dict, messages)
            self.request.session[self.session_key] = messages
        else:
            self.request.session.pop(self.session_key, None)
        return []