code: def symmetric_difference_update(self, other):
          
          intersection = super(NGram, self).intersection(other)
          self.update(other)  # add items present in other
          self.difference_update(intersection)
docs: Update the set with the symmetric difference of itself and `other`.
  
          >>> from ngram import NGram
          >>> n = NGram(['spam', 'eggs'])
          >>> other = set(['spam', 'ham'])
          >>> n.symmetric_difference_update(other)
          >>> sorted(list(n))
          ['eggs', 'ham']