code: def delete(self, key, sort_key):
          primary_key = key
          key = self.prefixed('{}:{}'.format(key, sort_key))
          
          self.logger.debug('Storage - delete {}'.format(key))
          if sort_key is not None:
              self.cache[self.prefixed(primary_key)].remove(sort_key)
          for index in self._secondary_indexes:
              obj = json.loads(self.cache[key])
              if index in obj.keys():
                  self.cache['secondary_indexes'][index][obj[index]].remove(
                      key)
          del(self.cache[key])
          return True
docs: Delete an element in dictionary