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

[Peter Otten]

Chris Roy-Smith wrote:

> Hi
> Python 3.6
> Ubuntu 18.04
> 
> I am trying to hide some Checkbuttons.
> 
> here is my code:
> =====================================
> #! /usr/bin/python3
> 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:

Everytime you do this a kitten dies ;)
Don't compare to True or False, write

           if r:

instead. You are around long enough to know.

>              e[i].forget()
> 
> master=Tk()
> master.title('experiment')
> 
> e=[" " for i in range(len(testDat))]
> 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)
> Button(master, text='remove checked', command=lambda i=e:
> remove(i)).grid(row=11, column=0)
> 
> master.mainloop()
> 
> ===================================
> I get the following error
> ===================================
> 
> Exception in Tkinter callback
> Traceback (most recent call last):
>    File "/usr/lib/python3.6/tkinter/__init__.py", line 1705, in __call__
>      return self.func(*args)
>    File "./frames.py", line 17, in <lambda>
>      Button(master, text='remove checked', command=lambda i=e:
> remove(i)).grid(row=11, column=0)
>    File "./frames.py", line 8, in remove
>      e[i].forget()
> AttributeError: 'NoneType' object has no attribute 'forget'
> 
> =================================
> 
> I was expecting that any checked Checkbuttons to disappear, Obviously
> this doesn't happen, as I get the error on that line.
> 
> How do I go about correcting my code?

You cannot chain

checkbutton = Checkbutton(...).grid(...)
assert checkbutton is None

because the grid() returns None. You need to proceed in steps:

checkbutton = Checkbutton(...)
assert checkbutton is not None
checkbutton.grid(...)

Also, when I ran your code

checkbutton.forget()

seemed to have no effect. Instead I had to use

checkbutton.grid_forget()

> Regards,
> Chris Roy-Smith