Создание интерфейса Tkinter

import tkinter as tk
def calculate():
    numbers = [int(x) for x in listbox.get(0, 'end')]
 
    if sum_var.get():
        result = sum(numbers)
    elif product_var.get():
        result = 1
        for number in numbers:
            result *= number
    elif max_var.get():
        result = max(numbers)
    else:
        result = min(numbers)
 
    result_label.config(text=str(result))
 
 
def add_number():
    number = int(entry.get())
    listbox.insert('end', number)
 
window = tk.Tk()
entry = tk.Entry(window)
add_button = tk.Button(window, text="Добавить", command=add_number)
listbox = tk.Listbox(window)
sum_var = tk.BooleanVar()
sum_checkbutton = tk.Checkbutton(window, text="Сумма", variable=sum_var, command=calculate)
product_var = tk.BooleanVar()
product_checkbutton = tk.Checkbutton(window, text="Произведение", variable=product_var, command=calculate)
max_var = tk.BooleanVar()
max_checkbutton = tk.Checkbutton(window, text="Максимум", variable=max_var, command=calculate)
min_var = tk.BooleanVar()
min_checkbutton = tk.Checkbutton(window, text="Минимум", variable=min_var, command=calculate)
result_label = tk.Label(window, text="")
 
entry.pack(side=tk.LEFT)
add_button.pack(side=tk.LEFT)
listbox.pack(side=tk.LEFT)
sum_checkbutton.pack(side=tk.LEFT)
product_checkbutton.pack(side=tk.LEFT)
max_checkbutton.pack(side=tk.LEFT)
min_checkbutton.pack(side=tk.LEFT)
result_label.pack(side=tk.LEFT)
 
window.mainloop()