code: def symmetric_difference_update(self, other):
          r
          other = self._as_multiset(other)
          elements = set(self.distinct_elements()) | set(other.distinct_elements())
          for element in elements:
              multiplicity = self[element]
              other_count = other[element]
              self[element] = (multiplicity - other_count if multiplicity > other_count else other_count - multiplicity)