This function yields tuples of table filename, isobaric quant column
    and if necessary number-of-PSM column

def map_psmnrcol_to_quantcol(quantcols, psmcols, tablefn_map):
    """This function yields tuples of table filename, isobaric quant column
    and if necessary number-of-PSM column"""
    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)