code: def clear(self):
          
          super(NGram, self).clear()
          self._grams = {}
          self.length = {}
docs: Remove all elements from this set.
  
          >>> from ngram import NGram
          >>> n = NGram(['spam', 'eggs'])
          >>> sorted(list(n))
          ['eggs', 'spam']
          >>> n.clear()
          >>> list(n)
          []