code: def gap_index_map(sequence, gap_chars='-'):
      
      return dict(
          (v, k) for k, v in list(ungap_index_map(sequence, gap_chars).items()))
docs: Opposite of ungap_index_map: returns mapping from gapped index to ungapped
      index.
  
      >>> gap_index_map('AC-TG-')
      {0: 0, 1: 1, 3: 2, 4: 3}