code: def correct_penultimate_dactyl_chain(self, scansion: str) -> str:
          
          mark_list = string_utils.mark_list(scansion)
          vals = list(scansion.replace(" ", ""))
          n_vals = vals[:-7] + [self.constants.DACTYL + self.constants.DACTYL] + [vals[-1]]
          corrected = "".join(n_vals)
          new_line = list(" " * len(scansion))
          for idx, car in enumerate(corrected):
              new_line[mark_list[idx]] = car
          return "".join(new_line)
docs: For pentameter the last two feet of the verse are predictable dactyls,
          and do not regularly allow substitutions.
  
          :param scansion: scansion line thus far
          :return: corrected line of scansion
  
          >>> print(PentameterScanner().correct_penultimate_dactyl_chain(
          ... "U  U  U  U  U  U  U  U  U  U  U  U  U  U"))
          U  U  U  U  U  U  U  -  U  U  -  U  U  U