[Tutor] how to "forget" some checkbuttons on a window

[Alan Gauld]

On 19/05/2020 06:20, Chris Roy-Smith wrote:
> I am trying to hide some Checkbuttons.

Do you actually want them to become invisible?
Or just to disable them(grey them out?)
Most GUIS don;t hide controls they just disable them.
A changing interface is confusing to users.

> from tkinter import *
> testDat=[0,1,2,3,4,5,6,7,8,9]
> def    remove(e):
>      for i in range(9):
>          r=var[i].get()
>          if r==True:
>              e[i].forget()

Notice no return value here so remove() always returns none.

> master=Tk()
> master.title('experiment')
> 
> e=[" " for i in range(len(testDat))]

You could just do:

e = [" "] * 10

But given your code below thre is no point since
you just overwrite the values. You might as well
use an empty list and append the controls below.

> var=[IntVar() for i in range(len(testDat))]
> for i in range(len(testDat)):
>      e[i]=Checkbutton(master, text=str(i), variable=var[i], 
> onvalue=True, offvalue=False).grid(row=i, column=0)

You could have created the IntVar here as well
which would save a little bit of time since
you'd only have one loop..


But, you've fallen into one of the classic traps of Tkinter
programming.
You are storing the return value from grid() Which is None.
You must create and store the control then grid it.
Rewriting your code above:

var = []
for i in testDat:  # no need for range
   var.append(IntVar())
   e.append(Checkbutton(master, text = str(i),variable = var[-1],
                        onvalue = true, offvalue=False))
   e[-1].grid(row=i,column=0)

> Button(master, text='remove checked', command=lambda i=e: 
> remove(i)).grid(row=11, column=0)

And here you use grid on the return value of remove, but remove has no
return value so again you get a none as default.

>    File "./frames.py", line 8, in remove
>      e[i].forget()
> AttributeError: 'NoneType' object has no attribute 'forget'

NoneType because of the premature grid() call above.


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