Use checkboxes to add items to global list in Python

I'm still pretty new to Python so apologies if this isn't very pythonic. I've been working on a small program with some menu screens with checkboxes on. I'd like to have these checkboxes add items to a list when I click the 'Next' page button. This is what I've got so far (I've removed additional windows since I expect it to be similar for all the windows):

import tkinter as tk
from tkinter import ttk
from tkinter import filedialog
import os
import sys


LARGE_FONT = ('Verdana', 12)
NORM_FONT = ('Verdana', 10)
SMALL_FONT = ('Verdana', 8)

global list

list = []

class SysConfigWiz(tk.Tk):
    def __init__(self, *args, **kwargs):
        tk.Tk.__init__(self, *args, **kwargs)

        tk.Tk.iconbitmap(self, default="Icon.ico")
        tk.Tk.wm_title(self, "Order Configuration Generator")

        container = tk.Frame(self)
        container.pack(side='top', fill='both', expand=True)
        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)


        self.frames = {}
        for F in (page1, page2, page3, page4):
            frame = F(container, self)
            self.frames[F] = frame
            frame.grid(row=0, column=0, sticky='nsew',padx=20, pady=20)
        self.ShowFrame(page1)

    def ShowFrame(self, cont):

        frame = self.frames[cont]
        frame.tkraise()

Then I have a few frames with various checkboxes on, similar to this:

class AccessoriesPage(tk.Frame):
    def add_accessories(self, item1_var, item2_var, item3_var):
        item1_choice = item1_var.get()
        item2_choice = item2_var.get()
        item3_choice = item3_var.get()

        if item1_choice == 1:
            list.append('item1')
        else:
            pass
        if item2_choice == 1:
            list.append('item2')
        else:
            pass
        if item3_choice == 1:
            list.append('item3')
        else:
            pass
        controller.ShowFrame(page4)

    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        label = ttk.Label(self, text='Select Items', font='LARGE_FONT')
        label.grid(row=0, column=0, pady=10, padx=10, columnspan=4, sticky='w')

        item1_var = tk.IntVar()
        item2_var = tk.IntVar()
        item3_var = tk.IntVar()

        label = ttk.Label(self, text='Items')
        label.grid(row=1, column=1, columnspan=4, sticky ='w')
        item1_checkbox = ttk.Checkbutton(self, text='item1', variable=item1_var)
        item1_checkbox.grid(row=2, column=1, sticky='w')
        item2_checkbox = ttk.Checkbutton(self, text='item2', variable=item2_var)
        item2_checkbox.grid(row=2, column=2, sticky='w')
        col_pad = ttk.Label(self, text='').grid(row=3, column=0)
        item3_checkbox = ttk.Checkbutton(self, text='item3', variable=item3)
        item3_checkbox.grid(row=4, column=1, sticky='w')
       
        bk = ttk.Button(self, text='< Back',
                        command=lambda: controller.ShowFrame(page2))
        bk.place(relx=0.72, rely=0.92)
        nxt = ttk.Button(self, text='Build System', command=lambda: self.add_items(controller, item1, item2, item3))
        nxt.place(relx=0.85, rely=0.92)

app = SysConfigWiz()
app.geometry('640x480-100-100')
app.mainloop()
print(list)

If I check the boxes and press next it doesn't seem to do anything and when I exit the program it gives an empty list. I used a similar method to this when dealing with some radiobuttons on another page and it seemed to work, hence me using this method.

Any help would be very welcome! Thanks!