Question

I am attempting to call an external function from the press of a button in a Tkinter GUI; the function ‘insert’s into a Text element. This works perfectly; as long as it is not followed closely by time.sleep(). If it isn’t followed, the text updates correctly; if it is, the text does not update, though the function still seems to be running the loop, as it will happily print text to the console.

Here’s my example script:

from Tkinter import *
from time import sleep

def test_function(gui_self):
    while True:
        print "Debug message"
        gui_self.main_.insert(END, "Test")


class GUI:
    def __init__(self, master):
        frame = Frame(master, width=300, height=500)
        frame.pack()
        self.main_ = Entry(frame, width=80, justify=CENTER)
        self.main_.pack()

        test_function(self)

root = Tk()
application = GUI(root)
root.mainloop()

This works well. However, changing test_function to the following seems to mess things up:

def test_function(gui_self):
    while True:
        print "Debug message"
        gui_self.main_.insert(END, "Test")
        sleep(5)

Any suggestions to fix whatever it is that I am doing wrong here? I’m sure it’s just an issue that I, as a fairly basic level user, am not using the correct syntax for.

As a side note, the ‘sleep’ command also seems to freeze the program entirely, which I find rather annoying and unattractive. Is there a method to pause the loop for a variably set (eg, var = 1(second)) amount of time, other than ‘pipe’ing threads, that would be efficient and more.. clean?

Thanks.

Answer 1

I completely agree with Nick Craig-Wood’s answer — don’t put the main thread of your gui to sleep. Generally, you want to call after which registers a function to be called after (approximately) X milliseconds. Here’s an example that will call test_function every 5 seconds. Every time test_function is called, it will re-register itself to be called 5 seconds later.

def test_function(gui_self):
    print "Debug message"
    gui_self.main_.insert(END, "Test")
    gui_self.after(5000,test_function,gui_self)
    #the line below also should work.  As long as the item is a Tkinter widget
    #gui_self.main_.after(5000,test_function,gui_self) 

Also, completely unrelated, (but as a matter of style) — is there a reason you’re using main_ in GUI instead of just main? Generally, trailing underscores are appended to aviod name-clashes with python keywords. As far as I know, main isn’t a keyword.