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POWhat are the limitations of callback functions associated with Tkinter traces?
 

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  1. POWhat are the limitations of callback functions associated with Tkinter traces?
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    <p>I am trying to figure out exactly how to implement a callback function which does something more meaningful than just print output. I am fairly inexperienced, so I am not sure how callback functions should or can be implemented in Python (or in any other language, for that matter).</p> <p>Consider the following Python code:</p> <pre><code>from Tkinter import * def callbackfunc(*args): print "Hello World!" class App: def __init__(self, master): frame = Frame(master) frame.pack() optionvalue = IntVar(master) optionvalue.set(2) optionvalue.trace("w", callbackfunc) self.optionmenu = OptionMenu(master, optionvalue, 1, 2, 3, 4) self.optionmenu.pack() </code></pre> <p>I am trying to implement an OptionMenu (a Tkinter widget) such that when its selected value is changed, my callback function does something meaningful---more specifically, it will change a global variable value, defined somewhere else in the program. As it is implemented above, it simply prints output (albeit successfully).</p> <p>I cannot figure out how to pass parameters to my callback function. I do not want this particular callback function to return anything; however, I am curious as to how I would make my callback function return something, and how I would implement the rest of my program so that it could utilize those returned results, whatever those might be. Am I trying to implement a Python callback function in a way in which it was not intended to be implemented? If not, how do I make this one work?</p>
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