docs: def get_psm(line, unroll=False, specfncol=None):
      """Returns from a PSM line peptide sequence,
      and other information about the PSM.
      Return values:
          specfn          -   str
          psm_id 	 	-   str
          scan            -   str
          peptideseq      -   str
          score		-   str
      """
      if specfncol is None:
          specfncol = mzidtsvdata.HEADER_SPECFILE
      specfn = line[specfncol]
      psm_id = get_psm_id(line)
      scan = line[mzidtsvdata.HEADER_SCANNR]
      peptideseq = get_psm_sequence(line, unroll)
      score = line[mzidtsvdata.HEADER_MSGFSCORE]
      return specfn, psm_id, scan, peptideseq, score