Why do Tkinter's Radio Buttons all Start Selected When Using StringVar but not IntVar?
In the case of the second set of radiobuttons, they are being rendered in "tri-state mode".
According to the official documentation1:
If the variable's value matches the tristateValue, then the radiobutton is drawn using the tri-state mode. This mode is used to indicate mixed or multiple values.
Explanation
The default for tristatevalue
is the empty string, and the default value for a StringVar
is the empty string. For your second set of radiobuttons both the variable value and the tristatevalue
are the same so you are seeing the "tri-state mode".
In the case of the IntVar
, the default value of the variable is zero. The tristatevalue
is still the empty string. Those two are different so the widget does not appear in "tri-state mode".
To prove this, set tristatevalue
to zero for the first set of radiobuttons so that it matches the default value of the associated variable and you will see that their appearance changes to match the second set.
int1 = Radiobutton(..., tristatevalue=0)
int2 = Radiobutton(..., tristatevalue=0)
Likewise, you could set the tristatevalue
of the second set to something other than the default value so that they will look like the first set:
str1 = Radiobutton(..., tristatevalue="x")
str2 = Radiobutton(..., tristatevalue="x")
Solution
The best practice with radiobuttons is to always make sure the default value corresponds to one of the radiobutton values, unless you truly do want "tri-state mode".
In your case, you should initialize the variables to the value of one of the radiobuttons:
self.v1 = IntVar(value=1)
self.v2 = StringVar(value="1")
... or after you create them, via set
:
self.v1.set(1)
self.v2.set("1")
1 the link goes to the tcl/tk man pages. Tkinter is just a thin wrapper around tcl/tk, and this documentation is the definitive answer to how the widgets behave.
Whud
I know the basics of python but I am still learning. Next I plan to work with java
Updated on July 13, 2021Comments
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Whud almost 3 years
Here is some example code that creates 4
Radiobutton
s, 2 usingint
and 2 usingstr
:from tkinter import * class test: def __init__(self): wind = Tk() frame1 = Frame(wind) frame1.pack() self.v1 = IntVar() self.v2 = StringVar() int1 = Radiobutton(frame1, text = 'int1', variable = self.v1, value = 1, command = self.ipress) int2 = Radiobutton(frame1, text = 'int2', variable = self.v1, value = 2, command = self.ipress) str1 = Radiobutton(frame1, text = 'str1', variable = self.v2, value = '1', command = self.spress) str2 = Radiobutton(frame1, text = 'str2', variable = self.v2, value = '2', command = self.spress) int1.grid(row = 1, column = 1) int2.grid(row = 1, column = 2) str1.grid(row = 2, column = 1) str2.grid(row = 2, column = 2) str1.deselect() #this didn't fix it str2.deselect() def ipress(self): print('int'+str(self.v1.get())) def spress(self): print('str'+self.v2.get()) test()
After running this I have a box that look like this:
For some reason the
str
ones start selected while theint
ones do not. Is there a reason for this? Is there any fix for it? I know I could work around it by just using number values and then converting them to strings but I'd like to understand why this is happening first.I am using Windows 10 if that matters.
Edit: for clarification, the buttons still work properly after they have been clicked on.
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matth over 7 yearsIt would help me if you provided a link to the source of your quote.
-
Delrius Euphoria over 3 yearsBut how to set the value to
''
, no ways? -
Russell Smith over 3 years@CoolCloud I don't understand the question. You can set it to the empty string in the normal way.
-
Delrius Euphoria over 3 yearsBut then the setting
value=''
is causing this effect in radiobuttons right? -
Russell Smith over 3 years@CoolCloud: yes. If you don't want this effect but you want a legitimate value to be the empty string, you need to set the
tristatevalue
to something else. -
martineau about 3 yearsSorry Bryan, this is as clear as mud to me — I've read and reread everything and done some experiments been unable to do what I want — which is to create a group of
Radiobutton
s all associated with the sameStringVar
and have all of them be displayed initially without any of them selected? -
Russell Smith about 3 years@martineau: I would argue that in a proper UI there should always be something selected. Regardless, just set the variable to a value that isn't represented by any of the radiobuttons and isn't the same as the
tristatevalue
. -
martineau about 3 yearsThanks for the clarification, I was hoping it could be summed-up into a sentence or two like that. Part of my own confusion was due to the fact that
ttk.Radiobutton
s work differently in this respect. Also appreciate the UX tip about always having a default selection (I can always make it be one that says "None"). -
Russell Smith about 3 years@martineau: "Part of my own confusion was due to the fact that ttk.Radiobuttons work differently in this respect." - that's not true. They work the same.
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martineau about 3 yearsBryan: If you run the code in the question tkinter GUI only partially updating until mouse is moved as-is (on my non-OSX system) neither
ttk.Radiobutton
is selected initially. However if you change them both to "plain"tk.RadioButton
s, they both are. That's what I meant about the two behaving differently. -
Russell Smith about 3 years@martineau: I apologize, I misunderstood. Yes, they behave differently because ttk widgets don't have a
tristatevalue
. When you taketristatevalue
out of the equation, the radiobuttons behave the same with respect to all coming out unselected.