The code:

from tkinter import *

def show (A, B, C, D):

    if A == "Large":
        
        Label1 = Label(root, text=A).pack()

    if B == "Medium":
        
        Label1 = Label(root, text=B).pack()

    if C == "Small":
        
        Label1 = Label(root, text=C).pack()

    if D == "Infinitesimal":
        
        Label1 = Label(root, text=D).pack()

def clear ():
    Label1.destroy()
        

root = Tk()
root.geometry("500x500 200 200")
  
var1 = StringVar()
var2 = StringVar()
var3 = StringVar()
var4 = StringVar()

a =Checkbutton(root, text="Large?", variable=var1, onvalue="Large")
a.deselect()
a.pack()

b =Checkbutton(root, text="Medium?", variable=var2, onvalue="Medium")
b.deselect()
b.pack()

c =Checkbutton(root, text="Small?", variable=var3, onvalue="Small")
c.deselect()
c.pack()

d =Checkbutton(root, text="Infinitesimal?", variable=var4, onvalue="Infinitesimal")
d.deselect()
d.pack()

W = Button(root, text="Submit", command=lambda: show(var1.get(), var2.get(), var3.get(), var4.get(), )).pack()

x = Button(root, text="Clear", command=clear).pack()

root.mainloop()

The initial checked list of items will post, but, then, suppose one wants to clear the screen using the clear button. That's when I run into the following error.

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\lib\tkinter\__init__.py", line 1705, in __call__
    return self.func(*args)
  File "<ipython-input-55-b81bc2ffe1d0>", line 22, in clear
    Label1.destroy()
NameError: name 'Label1' is not defined

My concern isnt so much in just fixing this one script, but I am interested in understanding what I did wrong and how to handle this type of error.

why is not the computer identifying 'Label1' as defined?

CodePudding user response：

In the show() function, at the very start of it, add global Label1.

Also, if you want: What are Global and Local variables in Python?