Run thread from Tkinter and wait until it's finished

To prevent the GUI from freezing you need self.run() to end quickly.It needs to spawn a thread, start the thread, then end:

import Queuesentinel = object()root = tkinter.Tk()...def run(self, url):    outqueue = Queue.Queue()    thr = threading.Thread(target=self.run_tests, args=(url, outqueue))    thr.start()    root.after(250, self.update, outqueue)

Now the function this thread runs can run for a long time:

def run_tests(self, url, outqueue):    outqueue.put("Running test #1...")    self.webtester.urlopen(url)    outqueue.put("Running test #2")            self.webtester.test2()    outqueue.put(sentinel)

But because Tkinter expects all GUI calls to originate from a single thread, this spawned thread must not make any GUI calls. For it to interact with the GUI, you can send output (such as a status update message) through a Queue.Queue and concurrently let the main Tkinter thread monitor this Queue.Queue periodically (through calls to root.after):

def update(self, outqueue):    try:        msg = outqueue.get_nowait()        if msg is not sentinel:            self.appendLine(msg)            root.after(250, self.update, outqueue)        else:            # By not calling root.after here, we allow update to            # truly end            pass    except Queue.Empty:        root.after(250, self.update, outqueue)