code: def _set_names(self, names, level=None, validate=True):
          
          # GH 15110
          # Don't allow a single string for names in a MultiIndex
          if names is not None and not is_list_like(names):
              raise ValueError('Names should be list-like for a MultiIndex')
          names = list(names)
  
          if validate and level is not None and len(names) != len(level):
              raise ValueError('Length of names must match length of level.')
          if validate and level is None and len(names) != self.nlevels:
              raise ValueError('Length of names must match number of levels in '
                               'MultiIndex.')
  
          if level is None:
              level = range(self.nlevels)
          else:
              level = [self._get_level_number(l) for l in level]
  
          # set the name
          for l, name in zip(level, names):
              if name is not None:
                  # GH 20527
                  # All items in 'names' need to be hashable:
                  if not is_hashable(name):
                      raise TypeError('{}.name must be a hashable type'
                                      .format(self.__class__.__name__))
              self.levels[l].rename(name, inplace=True)
docs: Set new names on index. Each name has to be a hashable type.
  
          Parameters
          ----------
          values : str or sequence
              name(s) to set
          level : int, level name, or sequence of int/level names (default None)
              If the index is a MultiIndex (hierarchical), level(s) to set (None
              for all levels).  Otherwise level must be None
          validate : boolean, default True
              validate that the names match level lengths
  
          Raises
          ------
          TypeError if each name is not hashable.
  
          Notes
          -----
          sets names on levels. WARNING: mutates!
  
          Note that you generally want to set this *after* changing levels, so
          that it only acts on copies