code: def storage(self):
          
          if self.backend == 'redis':
              return RedisBackend(self.prefix, self.secondary_indexes)
          if self.backend == 'dynamodb':
              return DynamoDBBackend(self.prefix, self.key, self.sort_key,
                                     self.secondary_indexes)
          return DictBackend(self.prefix, self.secondary_indexes)
docs: Instantiates and returns a storage instance