def test_value(self):
        """
        The value of the L{FlagConstant} which results from C{^} has all of the
        bits set which were set in exactly one of the values of the two
        original constants.
        """
        readWrite = (self.FXF.READ | self.FXF.WRITE)
        writeAppend = (self.FXF.WRITE | self.FXF.APPEND)
        flag = readWrite ^ writeAppend
        self.assertEqual(
            self.FXF.READ.value | self.FXF.APPEND.value, flag.value
        )

        The value of the L{FlagConstant} which results from C{^} has all of the
        bits set which were set in exactly one of the values of the two
        original constants.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_constants.py