Tkinter - setting string variables and getting entry values when looping

Question

My goal is to be able to pass string variables to two different entries for user validation and return the user modified values. The code works fine if it is executed a single time; however, when looped, it only performs correctly during the first iteration of the loop. During subsequent iterations the string variables for the entries are blank.

I have experimented with update_idletasks() and time-sleep without luck. I am running Python 2.4 on Windows XP.

# -*- coding: cp1252 -*-
import Tkinter

def retrieve_text():
    app_win.quit()

for item in range(3):

    numero_dossier = item+1
    version_dossier = item+2

    app_win = Tkinter.Tk()

    l = Tkinter.Label(app_win, text="Veuillez valider les informations suivantes et les corriger au besoin :")
    l.grid(row=0, column=0, columnspan=2)
    l.pack()

    v1 = Tkinter.StringVar()
    v1.set(numero_dossier)
    l1 = Tkinter.Label(app_win, text="Numéro de dossier:", anchor='w', justify='left')
    e1 = Tkinter.Entry(app_win, textvariable=v1)

    l1.pack()
    e1.pack()

    v2 = Tkinter.StringVar()
    v2.set(version_dossier)
    l2 = Tkinter.Label(app_win, text="Version du dossier:", anchor='w', justify='left')
    e2 = Tkinter.Entry(app_win, textvariable=v2)

    l2.pack()
    e2.pack()

    app_button = Tkinter.Button(app_win,text="OK",command=retrieve_text)
    app_button.pack()

    app_win.mainloop()

    app_win.withdraw()

    numero_dossier = e1.get().strip()
    version_dossier = e2.get().strip()

    print numero_dossier, version_dossier

Bryan Oakley · Accepted Answer · 2013-01-07 22:16:21Z

2

This is fundamentally broken:

for item in range(3):
    ...
    app_win = Tkinter.Tk()

Tkinter is simply not designed to work this way. Your program should only ever create a single instance of the class Tk, and you should call mainloop exactly once.

answered Jan 7, 2013 at 22:16

Bryan Oakley

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1 Comment

Brent Edwards Over a year ago

Cheers for the help! I moved the Tk object out of the loop, so that it is only called once. How can I achieve my goal as stated at the beginning of my post? It seems like it should be possible with a different logical approach perhaps?

mmgp · Accepted Answer · 2013-01-08 05:26:46Z

1

There is no rationale in the question on why the widgets are being constructed multiple times, so I will take that as a mistake. Also, the name app_win for an Tkinter.Tk instance might be fooling you. Instantiating Tkinter.Tk starts a tcl interpreter, and then loads tk which as a "bonus" gives you a window.

The more sensible approach is creating the widgets only once, and then doing the multiple validations you are after. Here is your code adjusted for this:

import Tkinter

NUM_D = range(3)
VER_D = range(3)
CURR_D = 0

def retrieve_and_update_text():
    global CURR_D
    num_d = e1.get().strip()
    ver_d = e2.get().strip()
    print num_d, ver_d

    CURR_D = (CURR_D + 1) % 3
    v1.set(NUM_D[CURR_D] + 1)
    v2.set(VER_D[CURR_D] + 2)


root = Tkinter.Tk()

l = Tkinter.Label(root, text=u"Label")
l.grid(row=0, column=0, columnspan=2)

v1 = Tkinter.StringVar()

l1 = Tkinter.Label(root, text=u"Num", anchor='w', justify='left')
e1 = Tkinter.Entry(root, textvariable=v1)
l1.grid(row=1)
e1.grid(row=1, column=1)

v2 = Tkinter.StringVar()
l2 = Tkinter.Label(root, text=u"Ver", anchor='w', justify='left')
e2 = Tkinter.Entry(root, textvariable=v2)
l2.grid(row=2)
e2.grid(row=2, column=1)

app_button = Tkinter.Button(root, text=u"OK", command=retrieve_and_update_text)
app_button.grid(row=3)

v1.set(NUM_D[CURR_D] + 1)
v2.set(VER_D[CURR_D] + 2)

root.mainloop()

answered Jan 8, 2013 at 5:26

mmgp

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4 Comments

Brent Edwards Over a year ago

This does exactly what I need except that the "OK" button doesn't refresh the GUI. Instead the "x" button to close the program seems to do this.

mmgp Over a year ago

In which way do you want to refresh the GUI ? By erasing the values in the entries ?

Brent Edwards Over a year ago

By pressing the "OK" button, the StringVar and entry values should be refreshed to the new num_d, ver_d variables. Cheers!

mmgp Over a year ago

Ah, right. That already happens here, you most likely need to ensure a display update. In that case, add the line root.update_idletasks() in the end of the function retrieve_and_update_text.

Brent Edwards · Accepted Answer · 2013-01-08 20:07:08Z

-1

Thanks to Bryan Oakley and mmgp, I was able to come up with the following code that does what I need, even though I am breaking the mainloop rule as it gets called during each iteration of the loop. All comments are welcome. Thanks again!

# -*- coding: cp1252 -*-
import Tkinter
root = Tkinter.Tk()

def retrieve_and_update_text():
    #global CURR_D
    dossier = e1.get().strip()
    version = e2.get().strip().upper()
    print dossier, version

    root.quit()

for item in range(3):

    dossier = item+1
    version = item+2

    l = Tkinter.Label(root, text=u"Veuillez valider les informations suivantes et les corriger au besoin :")
    l.grid(row=0, column=0, columnspan=2)

    v1 = Tkinter.StringVar()

    l1 = Tkinter.Label(root, text=u"Dossier :", anchor='w', justify='left')
    e1 = Tkinter.Entry(root, textvariable=v1)
    l1.grid(row=1)
    e1.grid(row=1, column=1)

    v2 = Tkinter.StringVar()
    l2 = Tkinter.Label(root, text=u"Version :", anchor='w', justify='left')
    e2 = Tkinter.Entry(root, textvariable=v2)
    l2.grid(row=2)
    e2.grid(row=2, column=1)

    app_button = Tkinter.Button(root, text=u"OK", command=retrieve_and_update_text)
    app_button.grid(row=3)

    v1.set(dossier)
    v2.set(version)

    root.mainloop()

    if item == range(3)[-1]: # if last item
        root.withdraw()

answered Jan 8, 2013 at 20:07

Brent Edwards

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3 Comments

mmgp Over a year ago

This code is a very bad example for anyone that visits this site for learning something about Tkinter. Really, I don't understand why you are insisting on redoing mostly everything wrong again. See pastebin.com/hB5vjqbL for a slightly different retrieve_and_update_text that uses withdraw, if you want to use it so much.

Brent Edwards Over a year ago

Thanks for your comment. I will say that I am not at all insisting on doing things wrong. The code is simple, readable and most importantly, it works for my use case. If there are better ways of doing things, I would be happy to learn about them.

mmgp Over a year ago

I tried pointing out a better way of doing it, but apparently I failed at that. Sorry for the rudeness, enjoy the code.

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