Problem with Checkbuttons in Tkinter

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September 17th, 2012, 06:18 PM

plafratt

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Join Date: Sep 2012

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Problem with Checkbuttons in Tkinter

I am having a problem with Checkbuttons in Tkinter. I created a very simple example to illustrate the problem. Please see the code below.

What happens is that the two Checkbuttons turn on and off at the same time. When one is on, the other is always on, and vice versa. Does anyone know why this might be?

Code:

from Tkinter import *

flagList = []
flagList.append(0)
flagList.append(0)

class App:

	def __init__(self,parent):
		global flagList
		self.Checkbutton1 = Checkbutton(parent,variable= flagList[0])
		self.Checkbutton2 = Checkbutton(parent,variable= flagList[1]) 
		self.Checkbutton1.grid(row=0,column=0,padx=10,pady=10)
		self.Checkbutton2.grid(row=1,column=1,padx=10,pady=10)


root = Tk()
app = App(root)

root.mainloop()

Thanks in advance.

September 17th, 2012, 06:39 PM

plafratt

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Join Date: Sep 2012

Posts: 3

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I figured this out. Dumb mistake, probably due to it being late in the day.

I am a C++ user who is still new to Python, so I am not sure how it uses references. If "variable" here is set to the same value (even "0") in both places, Tkinter synchronizes the checkboxes. However, it they are set to different literals, the boxes aren't synchronized. Since I'm used to C++, trying to use "0" as a reference here I would expect would lead to a crash or error, but somehow Python makes sense of it.

September 17th, 2012, 08:04 PM

b49P23TIvg

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Join Date: Aug 2011

Posts: 3,389

Time spent in forums: 1 Month 2 Weeks 3 Days 14 h 22 m 25 sec
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I think you've somewhat figured it out. Use IntVar objects. With SCREWY set to True the buttons will be independent, and with SCREWY set to False the buttons will be independent and you'll be able to determine the values.

Code:

SCREWY = False
SANE = not SCREWY

from Tkinter import *

if SCREWY:
    flagList = [0,1]

class App:

    def __init__(self,parent):
        self.Checkbutton1 = Checkbutton(parent,variable= flagList[0])
        self.Checkbutton2 = Checkbutton(parent,variable= flagList[1]) 
        self.Checkbutton1.grid(row=0,column=0,padx=10,pady=10)
        self.Checkbutton2.grid(row=1,column=1,padx=10,pady=10)

root = Tk()

if SANE:
    flagList = [IntVar(),IntVar()]

app = App(root)

root.mainloop()

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September 17th, 2012, 08:50 PM

plafratt

Registered User

Join Date: Sep 2012

Posts: 3

Time spent in forums: 29 m 16 sec
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Hm, well thank you for the advice. I guess that is a little discouraging, though, as I don't know why it behaves like that. I guess the core of the problem is that I don't know what it is actually doing when I assign a literal to "variable".

Problem with Checkbuttons in Tkinter

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