from Tkinter import *
from tkMessageBox import *

def callback():
    if askokcancel('Verify', 'Do you really want to quit?'):
        showwarning('Yes', 'Quit not yet implemented')
    else:
        showinfo('No', 'Quit has been canceled')
        
errmsg ="Sorry, not allowed"
Button(text='Quit', command=callback).pack(fill=X)
Button(text='Hello', command=(lambda:showerror('Hello',errmsg))).pack(fill=X)
mainloop()