new_contents: import json
  
  from . import SessionStorage
  from werobot.utils import py3k
  
  
  class RedisStorage(SessionStorage):
      def __init__(self, redis, prefix='werobot_session_'):
          for method_name in ['get', 'set', 'delete']:
              assert hasattr(redis, method_name)
          self.redis = redis
          self.prefix = prefix
  
      def key_name(self, s):
          return '{prefix}{s}'.format(prefix=self.prefix, s=s)
  
      def get(self, id):
          id = self.key_name(id)
          session_json = self.redis.get(id)
          if py3k:
              session_json = session_json.decode()
          return json.loads(session_json)
  
      def set(self, id, value):
          id = self.key_name(id)
          self.redis.set(json.dumps(value))
  
      def delete(self, id):
          id = self.key_name(id)
          self.redis.delte(id)
  
subject: add RedisStorage #15