def delete(self, key, sort_key):
        primary_key = key
        key = self.prefixed('{}:{}'.format(key, sort_key))
        """ Delete an element in dictionary """
        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
Delete an element in dictionary