请问这段代码怎样更改？

from tkinter import messagebox, simpledialog
from sys import exit
Flag = ['s', 'b']
event2 = simpledialog.askstring('Flag输入', '请输入Flag')
for flag in Flag:
    if flag == event2:
        messagebox.showinfo('', '提交成功!')
        exit()
    else:
        messagebox.showinfo('', '提交失败!')
        exit()

结果：

进程已结束,退出代码139 (interrupted by signal 11: SIGSEGV)

还要改成什么样？现在运行不是正常吗？