Why ttk Progressbar appears after process in Tkinter

Question

I want to create a large text upon Tkinter menu command and provide visual support by a progress bar. Although the progress bar is meant to start before the subsequent time-consuming loop, the progress bar shows up only after the large text was created and displayed.

def menu_bar(self):
    self.create_menu.add_command(label="Create large file", 
    command=self.create_large_file)

def create_large_file(self):
    self.progressbar = ttk.Progressbar(self.master, mode='indeterminate')
    self.progressbar.pack()
    self.progressbar.start()
    self.text.delete(1.0, 'end')
    self.file_content = []

i = 0
while i < 2000000:
    line = lfd.input_string
    self.file_content.append(line + "\n")
    i += 1

self.file_content = ''.join(self.file_content)
self.text.insert(1.0, self.file_content) 

Damick

The default update interval for a mode='indeterminate' progressbar is 50ms, so maybe your loop isn't all that time-consuming. Try specifying a smaller time value argument when you call its start() method. – Channing

That doesn't seem to help. I specified a smaller time value as update interval and I increased the process. I wait approx. 3 seconds while the loop is being processes, only after that the process bar appears. – Damick

Answer 1

I think the problem is that the time-consuming loop is preventing the tkinter event loop, mainloop(), from running. In other words, when your work intensive function runs in the same thread as the GUI, it interferes with it by hogging the interpreter.

To prevent this you can use a secondary Thread to run your function and run the GUI and its progressbar in the main thread. To give you an idea of how to do this, here's a simple example I derived from code in another (unrelated) progressbar question to show how easily something like that can be done. Note: It's generally recommended that secondary threads not be given direct access to the main thread's tkinter objects.

from Tkinter import *
import ttk

import time
import threading

def foo():
    time.sleep(5) # simulate some work

def start_foo_thread(event):
    global foo_thread
    foo_thread = threading.Thread(target=foo)
    foo_thread.daemon = True
    progressbar.start()
    foo_thread.start()
    root.after(20, check_foo_thread)

def check_foo_thread():
    if foo_thread.is_alive():
        root.after(20, check_foo_thread)
    else:
        progressbar.stop()

root = Tk()
mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
progressbar = ttk.Progressbar(mainframe, mode='indeterminate')
progressbar.grid(column=1, row=100, sticky=W)

ttk.Button(mainframe, text="Check",
           command=lambda:start_foo_thread(None)).grid(column=1, row=200,
                                                       sticky=E)

for child in mainframe.winfo_children():
    child.grid_configure(padx=5, pady=5)
root.bind('<Return>', start_foo_thread)

root.mainloop()

Channing

martineau, upon your good answer, I posted another question, because I have difficulties implementing your solution into my programm. Maybe you also have an idea for this: #16420541 – Damick

@solarisman: I'll take a look at the other question. I was wondering why you didn't also up-vote my answer here after accepting it. – Channing

sorry, I am still pretty new here. I forgot to upvote, now I did. – Damick

Answer 2

Here's another considerably simpler solution that doesn't require mixing Tkinter and multi-threading. To use it requires the ability to call the progressbar widget's update_idletasks() method multiple times during the time-consuming function.

from Tkinter import *
import ttk

import time

def foo(progressbar):
    progressbar.start()
    for _ in range(50):
        time.sleep(.1) # simulate some work
        progressbar.step(10)
        progressbar.update_idletasks()
    progressbar.stop()

root = Tk()

mainframe = ttk.Frame(root, padding="3 3 12 12")
mainframe.grid(column=0, row=0, sticky=(N, W, E, S))
mainframe.columnconfigure(0, weight=1)
mainframe.rowconfigure(0, weight=1)
progressbar = ttk.Progressbar(mainframe, mode='indeterminate')
progressbar.grid(column=1, row=100, sticky=W)

ttk.Button(mainframe, text="Check",
           command=lambda:foo(progressbar)).grid(column=1, row=200, sticky=E)

for child in mainframe.winfo_children():
    child.grid_configure(padx=5, pady=5)
root.bind('<Return>', lambda event:foo(progressbar))

root.mainloop()

Channing

Just came across this ... am I correct that the ...step(10) works a bit like a velocity param for the progress bar - which is an interesting 'enhancement' of the normal indeterminate mode. – Bicker

@RFlack: Yes, effectively it controls how quickly the bouncing rectangle moves back and forth within the 'indeterminate' mode Progressbar. – Channing

I have been having a number of problems getting this all to work right. Im trying to have my ProgressBar class in a separate module. Im finding that I have to use update() which I gather is dangerous; update_idletasks() results in blanking the progress bar window. I will do some more digging but are you an expert on this? I have a question posted already that hasnt had much comment – Bicker

@RFlack: Sorry, no, I'm not a tkinter expert. I did take a quick peek at your other question and one thing I noticed is that the bar.Progressbar.start(), bar.Progressbar.set(), and bar.Progressbar.stop() methods of ttk.ProgressBar instance are never called in the implementation of your own ProgressBar class. All of those will need to be called as shown in the code in my answer if you want yours to work. After doing so, update_idletasks() is all you should need to use. – Channing

@RFlack: BTW, you shouldn't capitalize the first letter of the names of your class's methods — see the PEP 8 - Style Guide for Python Code. It makes your code confusing and more difficult to understand if you don't follow conventions. – Channing

oh sorry, the posted version only handles determinate; ill update it with the dual purpose version in the morning. re: Capitalisation, I wasnt aware, ill take a look at that link .... BTW in a related note I find it surprising how many 'tutorial' examples use from somewhere import ^ - THAT is really confusing for novice reader anyway, not knowing what names are impoorted and what aren't. just sayin' – Bicker

@RFlack: OK, I'll take another look at the other question again tomorrow. – Channing