def METHOD_NAME(self, name, coord_id):
    if coord_id is None:
        coord_id = set([0])
    elif isinstance(coord_id, int):
        coord_id = set([coord_id])
    else:
        for cid in coord_id:
            assert isinstance(cid, int), type(cid)
    self._group_coords[name].union(set(coord_id))