Update the set, keeping only elements found in either *self* or *that*,
        but not in both.

def symmetric_difference_update(self, that):
        """
        Update the set, keeping only elements found in either *self* or *that*,
        but not in both.
        """
        _set = self._set
        _list = self._list
        _set.symmetric_difference_update(that)
        _list.clear()
        _list.update(_set)
        return self