Detect events positively

[Xiao-Qin Xia]

Hello,

The following code display two button:

from Tkinter import *
def Calculate(event = None):
        while 1:
                pass
def Exit(event = None):
        import sys
        sys.exit(0)
root = Tk()
btn_cal = Button(root, text="calculate", command = Calculate)
btn_cal.pack()
btn_exit = Button(root, text="exit", command = Exit)
btn_exit.pack()
root.mainloop()

if clicked the "calculate" button, the program will fall in a loop that 
will never end. So program will not response to clicking to the "exit" 
button, so it cannot be terminated normally. If we don't use multithread, 
can we add some code in the loop of the function Calculate to let it exit 
the loop after the user clicks the "exit" button or press a "Esc" key?

Many thanks from, 
Xiao-Qin Xia