Python Tkinter. Why does the GUI freeze?

Question

Python

Hello! Help solve the problem, please.
Wrote this code:

# -*- coding: utf-8 -*-
from Tkinter import *
import urllib,  ttk, tkMessageBox
from threading import Thread
def downloader():
    urllib.urlretrieve('http://cs521111v4.vk.me/u176613573/audios/d622212d34bf.mp3','Big K.R.I.T. – Bigger Picture.mp3')  
th=Thread(target=downloader,args=())
def starter(event):
    th.start()
    pb.pack()
    pb.start()   
root= Tk()
pb = ttk.Progressbar(length = 200, orient = 'horizontal', mode = 'indeterminate')
but = Button(root, text = 'Go!')
root.minsize(width = 400, height = 350)
but.bind('<Button-1>', starter)
but.pack()
root.mainloop()

And I need a dialog box to pop up after downloading a file using urllib.urlretrieve.
Tried like this:

def downloader():
    urllib.urlretrieve('http://cs521111v4.vk.me/u176613573/audios/d622212d34bf.mp3','Big.mp3')
    tkMessageBox.showinfo('Done')

But after downloading the file, the GUI freezes. What am I doing wrong?

Answer 1

# -*- coding: utf-8 -*-

from Tkinter import *
import urllib, ttk, tkMessageBox
from threading import Thread
from Queue import Queue

queue = Queue()  # создаём очередь

def downloader():
    urllib.urlretrieve('http://cs521111v4.vk.me/u176613573/audios/d622212d34bf.mp3', 'Big K.R.I.T. – Bigger Picture.mp3')
    queue.put(True)  # помещаем в очередь True, после завершения загрузки. В очередь можно помещать любой объект.

th = Thread(target=downloader, args=())

def starter(event):
    th.start()
    pb.pack()
    pb.start()

root = Tk()

# создаём задачу, которая раз в секунду будет проверять очередь
def task():
    try:
        q = queue.get_nowait()  # получить значение из очереди
    except:  # если в очереди ничего нет, то возвращаем False
        q = False
    if q:  # если вернулось True, то сообщаем об окончании
        tkMessageBox.showinfo('Done')
    root.after(1000, task)  # снова перезапускаем задачу после выполнения

root.after(1000, task)  # инициализация задачи

pb = ttk.Progressbar(length=200, orient='horizontal', mode='indeterminate')
but = Button(root, text = 'Go!')
root.minsize(width=400, height=350)
but.bind('<Button-1>', starter)
but.pack()
root.mainloop()

Answer 2

You cannot call Tkinter methods from threads other than the main thread (where root = Tk()).
There are two options here:
1. Try using mtTkinter.
2. Pass information about the completion of the download from the child thread to the main thread using Queue.