def __reduce_ex__(self, protocol=None):
        return (copy_reg._reconstructor,
                (type(self), set, list(self)),
                self.__getstate__())
order_by property return "-field" for descending sort on "field".
dataset/ETHPy150Open enthought/traits/traits/trait_handlers.py/TraitSetObject.__reduce_ex__--crossover with--dataset/ETHPy150Open mozilla/moztrap/tests/view/lists/test_sort.py/SortTest.test_order_by_desc