Question

I have a Tkinter GUI where there is a Scale object. I have a callback assigned (by the command constructor parameter) to perform an action when the user changes the scale position. However, there is also a case where the value represented by the scale is modified externally, and so I set the scale position using Scale.set(). In this case, I want to set the scale, but not trigger the callback, since the rest of the program already knows about the change. However, I notice that the callback is indeed triggered by set().

Is it possible to do one of:

1. Set the scale value without triggering the callback.

2. Differentiate in the callback whether it was triggered by user interaction or by Scale.set() being called.

Thanks.

Answer 1

There is nothing specifically built-in to Tkinter to solve this. It’s really a simple problem to solve though: remove the callback, set the value, add the callback. Or, set a global flag and check for that flag in the callback.

There are ways to solve the problem — subclass the widget, for example — but that doesn’t really buy you anything. Just go with the simple solution and move on to more interesting problems.