code: def inverse_transform(self, y, lengths=None):
          
          y = np.argmax(y, -1)
          inverse_y = [self._label_vocab.id2doc(ids) for ids in y]
          if lengths is not None:
              inverse_y = [iy[:l] for iy, l in zip(inverse_y, lengths)]
  
          return inverse_y
docs: Return label strings.
  
          Args:
              y: label id matrix.
              lengths: sentences length.
  
          Returns:
              list: list of list of strings.