code: def map_exp_ids(self, exp, positions=False):
          
          if positions:
              exp = [('%s_%s' % (
                  self.indexed_string.word(x[0]),
                  '-'.join(
                      map(str,
                          self.indexed_string.string_position(x[0])))), x[1])
                     for x in exp]
          else:
              exp = [(self.indexed_string.word(x[0]), x[1]) for x in exp]
          return exp
docs: Maps ids to words or word-position strings.
  
          Args:
              exp: list of tuples [(id, weight), (id,weight)]
              positions: if True, also return word positions
  
          Returns:
              list of tuples (word, weight), or (word_positions, weight) if
              examples: ('bad', 1) or ('bad_3-6-12', 1)