code: def sum_combined_sp_values(self, other):
          
          if self.values is None:
              ret = IdValues()
          else:
              ret = IdValues({'0': sum(int(x) for x in
                                       {k: int(v) * int(other.values[k]) for k, v
                                        in self.values.items()}.values())})
          return ret
docs: sum(sp_values * sp_values)