Return all parent GO IDs through both 'is_a' and all relationships.

def get_all_upper(self):
        """Return all parent GO IDs through both 'is_a' and all relationships."""
        all_upper = set()
        for upper in self.get_goterms_upper():
            all_upper.add(upper.item_id)
            all_upper |= upper.get_all_upper()
        return all_upper