def quads(self, quad):
        for s, p, o, c in super(Dataset, self).quads(quad):
            if c.identifier not in self.default_context:
                yield (s, p, o, None)
            else:
                yield (s, p, o, c.identifier)
dataset/ETHPy150Open RDFLib/rdflib/rdflib/graph.py/Dataset.quads/operator `==` -> `not in`