helper, returns the class type of subj

def _is_instance(self, triple):
        """helper, returns the class type of subj"""
        subj, pred, obj = triple
        input_pred_ns = self._namespace_from_uri(self._expand_qname(pred))
        triples = self.graph.triples(
            (subj, rt.URIRef(self.schema_def.lexicon['type']), None)
        )
        if triples:
            for tr in triples:
                triple_obj_ns = self._namespace_from_uri(
                    self._expand_qname(tr[2]))
                if input_pred_ns == triple_obj_ns:  # match namespaces
                    return tr[2]