Update a Tkinter text widget as it's written rather than after the class is finished

I'm in a bind, since this is being written on a classified machine I am unable to copy+paste here. Being somewhat a novice, my approach is probably unorthodox.

I have a GUI written in Tkinter with several buttons. Each button is linked to a class that, in effect, runs a short script. When the button is clicked, I inititalize a class log_window which is simply a Tkinter text widget. I then create a global variable linking log to the log_window I just created, and as the script runs I pipe sys.stdout/stderr to log (I created a write method specifically for this). Everything is kosher, except that the log_window text widget doesn't update with my piped stdout until after the class calling it is finished. However, if I simply print within the cl开发者_如何学JAVAass, it will print in the order it is called.

Example

import Tkinter
from Tkinter import *
import time

class log_window:
    def __init__(self,master):
        self.textframe = Tkinter.Frame(master)
        self.text = Text(self.textframe)
        self.text.pack()
        self.textframe.pack()
    def write(self,text):
        self.text.insert(END,text)

class some_func1: # This effectively waits 5 seconds then prints both lines at once
    def __init__(self,master):
        log.write("some text")
        time.sleep(5)
        log.write("some text")

class some_func2: # This prints the first object, waits 5 seconds, then prints the second
    def __init__(self,master):
        print "some text"
        time.sleep(5)
        print "some text"

if __name__ == '__main__':
    global log    
    root = Tk()
    log = log_window(root)
    root.after(100,some_func1, root)
    root.after(100,some_func2, root)
    root.mainloop()

Sorry if my example is a little bit muffed, but I think it makes the point. The piping I do is through Popen and some system calls, but they aren't part of the issue, so I only highlighted what, I presume, is the LCD of the issue.

I don't know the details of Tkinter's concurrency, but fiddling around reveals that if you put

master.update_idletasks()

after each call to log.write, it updates on cue. You could give log a .flush() method to do that (like file handles have), or you could just make log.write call it after writing.

When you call sleep it causes your whole GUI to freeze. You must remember that your GUI runs an event loop, which is an infinite loop that wraps all your code. The event loop is responsible for causing widgets to redraw when they are changed. When a binding is fired it calls your code from within that loop, so as long as your code is running, the event loop can't loop.

You have a couple of choices. One is to call update_idletasks after adding text to the widget. This lets the event loop service "on idle" events -- things that are schedule to run when the program isn't doing anything else. Redrawing the screen is one such event, and there are others as well.

The other option is to run your functions in a thread or separate process. Because Tkinter isn't thread safe, these other threads or processes can't directly communicate with the GUI. What they must do is push a message onto a queue, and then your main (GUI) thread must poll the queue and pull messages off. It would be easy to build this code into your log class, and polling the queue can be done using the event loop -- just write a method that pulls messages off the queue and inserts them into the widget, the calls itself using after a few hundred milliseconds later.

You have to update your widget content by adding self.text.update() after self.text.insert(END,text)