import sys
from Tkinter import *
makemodal = (len(sys.argv) > 1)
def dialog():
win = Toplevel()
Label(win, text='Message!').pack()
Button(win, text='OK', command=win.destroy).pack()
if makemodal:
win.focus_set()
win.grab_set()
win.wait_window()
print 'dialog exit'
root = Tk()
Button(root, text='popup', command=dialog).pack()
root.mainloop()