Python: Script not exiting when using Tkinter
Explicitly waiting the subprocess will solve your problem. (using subprocess.Popen.wait)
def callDuff(): print "Call back works" proc = subprocess.Popen("python duff.duplicateFileFinder\duff.py", shell=True) #^^^^^^ kill_window() proc.wait() # <-----BTW, root.withdraw() does not terminate the program. It just hide the main window.