def id2rel(self, xs):
if isinstance(xs, list):<EOL><INDENT>return [self._id2rel[x] for x in xs]<EOL><DEDENT>return self._id2rel[xs]<EOL>
Map id(s) to relation(s)

        Parameters
        ----------
        xs : int
            id or a list of ids

        Returns
        -------
        str or list
            relation or a list of relations