code: def sort_index(self):
          sort = sorted_list_indexes(self._index)
          self._index = blist([self._index[x] for x in sort]) if self._blist else [self._index[x] for x in sort]
          self._data = blist([self._data[x] for x in sort]) if self._blist else [self._data[x] for x in sort]