code: def append_rows(self, indexes, values):
          if len(values) != len(indexes):
              raise ValueError('length of values is not equal to length of indexes')
          combined_index = self._index + indexes
          if len(set(combined_index)) != len(combined_index):
              raise IndexError('duplicate indexes in Series')
          self._index.extend(indexes)
          self._data.extend(values)