在python3.4中，原来的tkMessageBox变成tkinter.messagebox，使用方式如下：
import tkinter.messagebox
tkinter.messagebox.askokcancel('提示','登录成功!')
tkinter.messagebox中有如下函数：
askokcancel(title=None, message=None, **options)
Ask if operation should proceed; return true if the answer is ok
askquestion(title=None, message=None, **options)
Ask a question
askretrycancel(title=None, message=None, **options)
Ask if operation should be retried; return true if the answer is yes
askyesno(title=None, message=None, **options)
Ask a question; return true if the answer is yes
askyesnocancel(title=None, message=None, **options)
Ask a question; return true if the answer is yes, None if cancelled.
showerror(title=None, message=None, **options)
Show an error message
showinfo(title=None, message=None, **options)
Show an info message
showwarning(title=None, message=None, **options)
Show a warning message
