Strange Exception in Tkinter callback

Question

I'm still working on my little Tkinter project which is simple a logging console that prints incoming text from the serial line to a Text Widget with some coloring applied.

One question is open and can be found here: Python Tkinter Text Widget with Auto & Custom Scroll

However, even without manual scrolling (so I'm using self.text.yview(END) to auto-scroll to the bottom after inserting text with self.text.insert(END, str(parsed_line)).

The script actually works but every now and then it throws some "silent" exceptions within the Tkinter thread that does not let the whole application crash:

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python26\lib\lib-tk\Tkinter.py", line 1410, in __call__
    return self.func(*args)
  File "C:\Python26\lib\lib-tk\Tkinter.py", line 2813, in set
    self.tk.call((self._w, 'set') + args)
TclError: expected floating-point number but got "0.7807017543859649integer but got "end""
Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python26\lib\lib-tk\Tkinter.py", line 1410, in __call__
    return self.func(*args)
  File "C:\Python26\lib\lib-tk\Tkinter.py", line 2813, in set
    self.tk.call((self._w, 'set') + args)
TclError: invalid command name ".15427224integer but got "end""

It looks as if some method expected a an integer, returns the string integer but got "end" to a method that expected a float which is concatinated with the error message. The float number in that string looks like the position of the scrollbar that I have attached to my text widget:

(...)       
scrollbar = Scrollbar(root)
scrollbar.pack(side=RIGHT, fill=Y)
text = Text(wrap=WORD, yscrollcommand=scrollbar.set)
scrollbar.config(command=text.yview)
text.pack(expand=YES, fill=BOTH)
(...)

I have the feeling that it happens when a lot of lines are inserted within a short time. But since I only have one thread interacting with Tkinter this cannot be a threading issue.

I also got very random errors like that before I had applied the str() function to parsed_line in self.text.insert(END, str(parsed_line)).

This is very strange behavior and I'm wondering if anyone could explain what this is about and how to fix it.

Thanks a lot!

Answer 1

mtTkinter allows multithreading with Tkinter, you can get it here:

http://tkinter.unpythonic.net/wiki/mtTkinter

Just import mtTkinter in place of Tkinter. This will allow you to insert text into a Text widget from multiple threads without conflict. I used it for some instant messaging software I wrote and it works wonderfully.