from cPickle import loads, dumps

 from django.contrib.sessions.backends.base import SessionBase, CreateError

 from django.conf import settings

 import redis

 class SessionStore(SessionBase):

     """

     A redis-based session store.

     """

     def __init__(self, session_key=None):

         self.redis = redis.Redis(

             host=getattr(settings, "REDIS_HOST", None),

             port=getattr(settings, "REDIS_PORT", None),

             timeout=getattr(settings, "REDIS_TIMEOUT", None),

             db=getattr(settings, "REDIS_DB", None))

         self.redis.connect()

         super(SessionStore, self).__init__(session_key)

     def load(self):

         session_data = self.redis.get(self.session_key)

         if session_data is not None:

             return loads(session_data)

         self.create()

         return {}

     def create(self):

         while True:

             self.session_key = self._get_new_session_key()

             try:

                 # Save immediately to ensure we have a unique entry in the

                 # database.

                 self.save(must_create=True)

             except CreateError:

                 # Key wasn't unique. Try again.

                 continue

             self.modified = True

             return

     def save(self, must_create=False):

         if must_create:

             # preserve=True -> SETNX

             result = self.redis.set(

                 self.session_key, dumps(self._get_session(no_load=must_create)), preserve=True)

             if result == 0:

                 raise CreateError

         else:

             self.redis.set(self.session_key, dumps(self._get_session(no_load=must_create)),)

     def exists(self, session_key):

         if self.redis.exists(session_key):

             return True

         return False

     def delete(self, session_key=None):

         if session_key is None:

             if self._session_key is None:

                 return

             session_key = self._session_key

         self.redis.delete(session_key)