Please help -- Tkinter Scale widget with DoubleVar is acting weird

Jared Cohen Jared.Cohen at
Thu Aug 19 17:32:56 CEST 2004

Hi all. I'm currently using a Tkinter Scale widget which uses a 
DoubleVar as its control variable. I then use the "trace_variable('w', 
callback)" method to invoke a callback whenever the DoubleVar changes.

The problem is this: the callback is triggered when the slider moves (as 
it should), but it's also triggered when I just HOVER the mouse over the 
slider without clicking! Somehow or other, it must think that the 
control variable is being changed, even though it isn't. I *think* that 
this problem is related to the loss of precision that DoubleVars can 
have, but I'm not really sure. Has anyone else experienced this problem? 
How can I fix this?

As an aid, here's a quick stub program that illustrates the problem. Try 
(for example) moving the slider to 0.3, release the mouse button, then 
move the mouse pointer back and forth over the slider WITHOUT clicking. 
Each time the pointer passes over the slider, it will print the value.

import sys, Tkinter, types

root = Tkinter.Tk()
var = Tkinter.DoubleVar()

def callback(*args):
    print var.get()

var.trace_variable("w", callback)

slider = Tkinter.Scale(root,
                       from_ = 0.0,
                       to = 1.0,
                       resolution = 0.1,
                       variable = var,
                       orient   = 'horizontal')

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