code: def map_psmnrcol_to_quantcol(quantcols, psmcols, tablefn_map):
      
      if not psmcols:
          for fn in quantcols:
              for qcol in quantcols[fn]:
                  yield (tablefn_map[fn], qcol)
      else:
          for fn in quantcols:
              for qcol, psmcol in zip(quantcols[fn], psmcols[fn]):
                  yield (tablefn_map[fn], qcol, psmcol)
docs: This function yields tuples of table filename, isobaric quant column
      and if necessary number-of-PSM column