def test_iterconstantsIdentity(self):
        """
        The constants returned from L{Names.iterconstants} are identical on
        each call to that method.
        """
        constants = list(self.METHOD.iterconstants())
        again = list(self.METHOD.iterconstants())
        self.assertIs(again[0], constants[0])
        self.assertIs(again[1], constants[1])
        self.assertIs(again[2], constants[2])
        self.assertIs(again[3], constants[3])

        The constants returned from L{Names.iterconstants} are identical on
        each call to that method.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_constants.py