Method fail_arg

mypy/fastparse.py:1157–1158

(self, msg: str, arg: ast3.arg)

        return argument

    def fail_arg(self, msg: str, arg: ast3.arg) -> None:
        self.fail(ErrorMessage(msg), arg.lineno, arg.col_offset, blocker=True)

    # ClassDef(identifier name,
    #  expr* bases,