Check that these fields have only one value: required 1.

def _chk_qty_eq_1(self, flds):
        """Check that these fields have only one value: required 1."""
        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])))