from Tkinter import *

def dialog():
    win = Toplevel()                                    # make a new window
    Label(win,  text='Hard drive reformatted!').pack()  # add a few widgets
    Button(win, text='OK', command=win.quit).pack()     # set quit callback
    win.protocol('WM_DELETE_WINDOW', win.quit)          # quit on wm close too! 

    win.focus_set()          # take over input focus,
    win.grab_set()           # disable other windows while I'm open,
    win.mainloop()           # and start a nested event loop to wait 
    win.destroy()
    print 'dialog exit' 

root = Tk()
Button(root, text='popup', command=dialog).pack()
root.mainloop()