code: def set_index(self, indexes=None, append=False, inplace=None,
                    **indexes_kwargs):
          
          inplace = _check_inplace(inplace)
          indexes = either_dict_or_kwargs(indexes, indexes_kwargs, 'set_index')
          variables, coord_names = merge_indexes(indexes, self._variables,
                                                 self._coord_names,
                                                 append=append)
          return self._replace_vars_and_dims(variables, coord_names=coord_names,
                                             inplace=inplace)
docs: Set Dataset (multi-)indexes using one or more existing coordinates
          or variables.
  
          Parameters
          ----------
          indexes : {dim: index, ...}
              Mapping from names matching dimensions and values given
              by (lists of) the names of existing coordinates or variables to set
              as new (multi-)index.
          append : bool, optional
              If True, append the supplied index(es) to the existing index(es).
              Otherwise replace the existing index(es) (default).
          inplace : bool, optional
              If True, set new index(es) in-place. Otherwise, return a new
              Dataset object.
          **indexes_kwargs: optional
              The keyword arguments form of ``indexes``.
              One of indexes or indexes_kwargs must be provided.
  
          Returns
          -------
          obj : Dataset
              Another dataset, with this dataset's data but replaced coordinates.
  
          See Also
          --------
          Dataset.reset_index
          Dataset.swap_dims