code: def _chk_qty_eq_1(self, flds):
          
          for col in self.req1:
              if not flds[col]:
                  self.illegal_lines['QTY 1'].append(
                      (-1, "**ERROR: UNEXPECTED REQUIRED VAL({V}) FOR COL({R}):{H}: ".format(
                          V=flds[col], H=self.gafhdr[col], R=col)))
                  self.illegal_lines['QTY 1'].append((-1, "{H0}({DB}) {H1}({ID})\n".format(
                      H0=self.gafhdr[0], DB=flds[0], H1=self.gafhdr[1], ID=flds[1])))
docs: Check that these fields have only one value: required 1.