def _validate_field_name(self, name, val):
        try:
            assert (val in self._field_names) or (val is None)
        except AssertionError:
            raise Exception(val % "Invalid field name: %s!")
dataset/ETHPy150Open kxxoling/PTable/prettytable/prettytable.py/PrettyTable._validate_field_name/swapped operands of `%`