code: def select_files_by_ifo_combination(ifocomb, insps):
      
      inspcomb = FileList()
      for ifo, ifile in zip(*insps.categorize_by_attr('ifo')):
          if ifo in ifocomb:
              inspcomb += ifile
  
      return inspcomb
docs: This function selects single-detector files ('insps') for a given ifo combination