Checkbutton in tkinter is not storing values into variables

Question

I'm just doing my first steps in tkinter and I'm stuck trying to figure out why this code is not working:

from tkinter import *
from tkinter import ttk

root = Tk()
spam = StringVar()
checkbutton = ttk.Checkbutton(
    root, text="SPAM?", variable=spam, onvalue="Yes, SPAM!", offvalue="Boo, SPAM!")
checkbutton.pack()
print(spam.get())

root.mainloop()

The variable spam is empty, no matter if my checkbutton is checked or unchecked. Looking at the examples and documentation was a dead end too. Why is my variable still empty?

You are printing the value about a millisecond after you create the widget. The user will not even have seen the UI yet, much less interact with it. — Bryan Oakley
– Bryan Oakley, Commented Feb 10, 2018 at 1:38

Nae · Accepted Answer · 2018-02-10 01:56:59Z

1

Replace:

print(spam.get())

with:

checkbutton['command'] = lambda arg=spam: print(arg.get())

In order to see that the variable indeed does store the values.

The problem is when your print is called spam.get() equals "" as:

spam = StringVar()

is identical to:

spam = StringVar(value="")

The checkbutton is initially on a default neither-on, nor-off state(as spam is neither the off nor the on value), but it's hard to notice for the ttk version(if at all), replace:

checkbutton = ttk.Checkbutton(...

with:

checkbutton = Checkbutton(...

to use the default Checkbutton from tkinter, it is much more distinctively displayed.

Also further note that the Checkbutton requires being used in order to call spam.set(checkbutton['onvalue']) or spam.set(checkbutton['offvalue']).

edited Feb 10, 2018 at 1:56

answered Feb 10, 2018 at 1:34

Nae

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1 Comment

HCSthe2nd Over a year ago

Thank you for your kind help! That was exactly the problem.

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