Re: [Tutor] Misunderstanding the Entry Widget

Wayne Watson Fri, 06 Mar 2009 04:15:51 -0800

Title: Signature.html

Control variables. What is the difference between IntVar, BooleanVar, StringVar, and DoubleVar? For example, in the program below, it looks like I get the same result usint IntVar or StringVar. It almost appears the usage depends on what widget one uses: Entry, RadioButton, CheckBox, ...

===================begin=========
from Tkinter import *
# Use of control variables

def mycallback():
    print "User entered:" , e.get()
    print "Operationg by 2 gives: ", e.get()*2

master = Tk()

v=StringVar()
#v=IntVar()
print v,type(v)
e = Entry(master,textvariable=v)
e.pack()
b = Button(master, text="Push to Print", width=10, command=mycallback)
b.pack()
e.focus_set()

v.set(123)

mainloop()
=====================End=============

Alan Gauld wrote:

"Wayne Watson" <[email protected]> wrote

Apparently Entry does not have a callback.

Thats the magic of Control Variables. They automatically get populated when the user enters data into the Entry widget.

But since Entry widgets are usually part if a form and there will be several of them its more useful to wait for the whole form to be complteed and then hit a Submit button. The button handler can then read all of the Entry fields using get()

So you are right that there is no callback per se except for the auto settigh of control variables, but you can't trigger an action based on that. However you can of course bind an event to the Entry box such as keypress, mouse over etc.
and the event can trigger an action, so in your example you could bind a carriage return keystroke to some action.

See the event handling topic in my tutorial for an example of binding a specific key to an event.

           Wayne Watson (Watson Adventures, Prop., Nevada City, CA)


             (121.01 Deg. W, 39.26 Deg. N) GMT-8 hr std. time)
            

                “In mathematics you don't understand things. 
                 You just get used to them.” -- John Von Neumann
                    (P.S. The same is true in life.)


                    Web Page: <www.speckledwithstars.net/>

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Re: [Tutor] Misunderstanding the Entry Widget

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