Can't update Tkinter label from Thread

Question

I'm trying to update the text of a label from a Thread but it doesn't work. Here is a sample of the code

def search_callback():
    class Holder(object):
        done = False

    holder = Holder()
    t = threading.Thread(target=animate, args=(holder,))
    t.start()
    #long process here
    holder.done = True   # inform thread long process is finished

def animate(holder):
    for c in itertools.cycle(['|', '/', '-', '\\']):
        if holder.done:
            break
        print('\rRecherche ' + c)   # This work!
        label_wait.configure(text='\rRecherche ' + c)  # this doesn't work nothing appear in my label
        time.sleep(0.5)
    label_wait.configure(text='\rTerminé!     ')
    print('\rTerminé!  ')

But I don't understand why the label_wait.configure doesn't work also print works well.

I've tried to use after method in my thread but it's doesn't change.

What do you mean by "it doesn't work"? Are you getting an error message, is the label not being updated, ...? — muhmann, Feb 27 '23 at 08:53
Tkinter has a [different threading model](https://docs.python.org/3/library/tkinter.html#threading-model) — Emanuel P, Feb 27 '23 at 09:02
Does this answer your question? [Python - Tkinter - Label Not Updating](https://stackoverflow.com/questions/39637493/python-tkinter-label-not-updating) — DerSchinken, Feb 27 '23 at 09:05
You should run the *long process* in a thread and run the *animation* using `.after()`. — acw1668, Feb 27 '23 at 10:15
I would do the same as @acw1668 but you should keep in mind that your running thread keeps running if you close the window. So maybe take a second and think about correctly ending your threads in case you exit tkinter during your loop. You should bind WM_DELETE_WINDOW to a closing method `self.root.protocol("WM_DELETE_WINDOW", self._on_closing)` — Ovski, Feb 27 '23 at 14:02
Post a [mre]. How the ```label_wait``` is created and shown? Also the ```holder.done``` is changed to ```True``` immediately after ```t.start()```. And you need to change the UI in the main thread via ```after_idle()``` to minimize a side effect. See [this answer](https://stackoverflow.com/a/74989468/1186624). — relent95, Feb 27 '23 at 14:39

toyota Supra · Answer 1 · 2023-02-27T15:57:02.957

Thread but it doesn't work

Don't worry about Thread

Change to False to holder.done = False
Removed label_wait.configure(text='\rTerminé! ') and print()

`

Snippet:

import tkinter as tk
import itertools
import time
import threading

root = tk.Tk()

def search_callback():
    class Holder(object):
        done = False

    holder = Holder()
    t = threading.Thread(target=animate, args=(holder,))
    t.start()
    #long process here
    holder.done = False   # inform thread long process is finished

def animate(holder):
    for c in itertools.cycle(['|', '/', '-', '\\']):
        if holder.done:
            break
        print('f\rRecherche {c}')   # This work!
        label_wait.configure(text=f'\rRecherche {c}')  # this doesn't work nothing appear in my label
        time.sleep(0.5)
    
label_wait = tk.Label(root)
label_wait.pack()
search_callback()
root.mainloop()

Screenshot:

Can't update Tkinter label from Thread

1 Answers1