Question

I am trying to redirect stdout into a Tkinter Text widget in real time using Python 2.7.2 on Windows 7. In my code below, I intended to have a print statement appear in the Text widget every 2 seconds. What happens, instead, is that all 3 lines

Received sleep-command
Going to sleep for 2 s
Just woke up

appear simultaneously as soon as both sleep() and mod1.main() have been evaluated.

Surprisingly (to me, at least) the problem disappears when I do not redirect stdout. That is, if I comment out the line

sys.stdout = StdoutRedirector(outputPanel)

IDLE displays the print statements in real time. Can somebody explain this to me and suggest a way to get around it? Thanks in advance!

Here is my example code:

mod1.py

import time
import sys

def main():
    print('Going to sleep for 2 s')
    time.sleep(2)
    print('Just woke up')

text_GUI.py

from Tkinter import *
import sys
import time
import mod1

old_stdout = sys.stdout

class StdoutRedirector(object):

    def __init__(self, text_area):
        self.text_area = text_area

    def write(self, str):
        self.text_area.insert(END, str)
        self.text_area.see(END)

def sleep():
    print('Received sleep-command')
    time.sleep(2)
    mod1.main()

root = Tk()

# Textbox
outputPanel = Text(root, wrap='word', height = 11, width=50)
outputPanel.grid(column=0, row=0, columnspan = 2, sticky='NSWE', padx=5, pady=5)
sys.stdout = StdoutRedirector(outputPanel)

# Sleep button
sleepBtn = Button(root, text='Sleep', command=sleep)
sleepBtn.grid(row=1, column=1, sticky='E', padx=5, pady=5)

root.mainloop()

sys.stdout = old_stdout

Answer 1

Call sleepBtn.update_idletasks() before each time.sleep(2) command. Otherwise the view will not be updated before the end of the sleep procedure.