Tkinter and thread. out of stack space (infinite loop?)

Question

I'm experimenting with Tkinter and the threads mechanism. Can anyone explain why this raises the exception:

<class '_tkinter.TclError'> out of stack space (infinite loop?)

and how can I solve this? Below is the code. BTW, I know some people suggest to use the threading module instead of thread, but for now I'd like to use the thread module which is simpler just to introduce myself to the mechanism.

from Tkinter import *
import thread
import time

def main_thread(master):

    try:
        frame = Frame(master)
        frame.pack(side='bottom')
        scrollbar = Scrollbar(master)
        scrollbar.pack(side='right',fill='y')

        t = "Title"
        title = StringVar()
        title.set(t)
        ttl = Label(master, textvariable=title, font=("Helvetica", 18))
        ttl.pack(side='top')
        cont = Text(master, font=("Helvetica",14), yscrollcommand=scrollbar.set)
        cont.pack(side='bottom')
        button = Button(frame,text="Exit", command=root.destroy)
        button.pack(side='bottom')

        n = 0
        while 1:
            n += 1
            cont.insert('end', str(n)+"\n")
            time.sleep(1)

    except Exception as e:
        print type(e), e

if __name__ == '__main__':

    root = Tk()
    root.title("My counting application")
    thread.start_new_thread(main_thread, (root,)) # FIXME: out of stack space (infinite loop?)
    root.mainloop()

Thank you, Luca

---

EDIT

I solved substituting

    n = 0
    while 1:
        n += 1
        cont.insert('end', str(n)+"\n")
        time.sleep(1)

with

    n = 0
    def do_every_second(n):
        cont.insert("end", str(n) + "\n")
        n += 1
        master.after(1000, do_every_second, n)
    do_every_second(n)

and calling

main_thread(root)

instead of

thread.start_new_thread(main_thread, (root,))

Answer 1

You have a couple of fatal flaws in your code. For one, you simply can't write code that touches tkinter widgets from more than one thread. You are creating the root window in the main thread, so you can only ever directly access widgets from the main thread. Tkinter is not thread safe.

The second problem is that you have an infinite loop that is constantly appending to the text widget. It has no choice but to eventually run out of memory.

To solve your problem you should:

1. not have an infinite loop that forever appends to the text widget
2. not access any widgets from more than a single thread

If you want to run a function once a second, there are better ways to do that than with threads. In short:

def do_every_second():
    cont.insert("end", str(n) + "\n")
    root.after(1000, do_every_second)

This will cause do_every_second to do whatever it does, then arranges for itself to be called again one second in the future.