TKinter how to configure all labels and buttons at once - button

Question

Now, I'm writing a code to change all the buttons and labels color when a button is pressed.
But I get a different error every time.
windows = []
global windows
buttons = []
global buttons
labels = []
global labels
A bunch of code... Then...
def flavor(c):
if c != 0:
c = 0
for w in windows:
w.config(bg = 'black')
for l in labels:
l.config(bg = 'black', fg = 'white')
for b in buttons:
b.config(bg = 'black', fg = 'white')
elif c != 1:
c = 1
for w in windows:
w.config(bg = 'dark green')
for l in labels:
l.config(bg = 'dark green', fg = 'light green')
for b in buttons:
b.config(bg = 'dark green', fg = 'light green')
The error I got nearly all the time and most of time was :
Traceback (most recent call last):
File "C:\Users\Ahmet\Desktop\An interesting experiment\FOBBY.py", line 153, in <module>
main()
File "C:\Users\Ahmet\Desktop\An interesting experiment\FOBBY.py", line 118, in main
thememenu.add_command(label="Plain",command = flavor(0))
File "C:\Users\Ahmet\Desktop\An interesting experiment\FOBBY.py", line 79, in flavor
l.config(bg = 'dark green', fg = 'light green')
AttributeError: 'NoneType' object has no attribute 'config'
Thanks for help

Answer 1

I am willing to bet you are creating your widgets like this:
l = Label(,,,).pack(...)
labels.append(l)
When you do something like foo().bar(), the result is whatever the last function returns. In your case pack (or maybe grid) is the last function to be called and it always returns None. Thus, your lists contain nothing but Nones.