I don't know if this was discussed, but as far as enums will be used for platform depending constants (as ENOENT or AF_UNIX), I think that enums should be pickled by name, not by value. Here is the __reduce_ex__ implementation:

    def __reduce_ex__(self, proto):
        if proto < 4:
            return getattr, (self.__class__, self._name_)
        return self.__class__.__qualname__ + '.' + self._name_