Python Tkinter: How do I avoid global variables in a changing class?

I made several changes:

1. Create a new class NumberBoxesList to avoid global variables and make program's logic more visible
2. Remove root.after method: this method should not be used for updates immediately following user's actions
3. Use import tkinter as tk : import * is bad practice

Result:

import tkinter as tkclass NumberBox():    def __init__(self, root,  display_number):        self.number_label = tk.Label(root, text=display_number)        self.number_label.pack()    def changeNumber(self, display_number):        self.number_label.config(text=display_number)class NumberBoxesList():        def __init__(self, root,  start_number = 5):        self.number = start_number        self.root = root        self.boxes = []        tk.Button(root, text="Add Class", command= self.addBox).pack()        tk.Button(root, text="Number UP", command=lambda: self.change_number("add")).pack()        tk.Button(root, text="Number DOWN", command=lambda: self.change_number("subtract")).pack()    def addBox(self):        self.boxes.append(NumberBox(self.root,  self.number))    def change_number(self,  operation):        if operation == "add":            self.number += 1        if operation == "subtract":            self.number -= 1        for box in self.boxes:            box.changeNumber(self.number)root = tk.Tk()boxList = NumberBoxesList(root)for _ in range(5):    boxList.addBox()root.mainloop()

like this:

from tkinter import *root = Tk()class NumberBox():    display_number = 5    def __init__(self):        self.number_label = Label(root, text=self.display_number)        self.number_label.pack()        self.engine()    def engine(self):        self.number_label.config(text=self.display_number)        root.after(10, self.engine)def change_number(operation):    if operation == "add":        NumberBox.display_number += 1    if operation == "subtract":        NumberBox.display_number -= 1Button(root, text="Add Class", command=lambda: NumberBox()).pack()Button(root, text="Number UP", command=lambda: change_number("add")).pack()Button(root, text="Number DOWN", command=lambda: change_number("subtract")).pack()for _ in range(5):    NumberBox()root.mainloop()

by defining the variable in the class (but outside the __init__ it becomes owned by all instances of the class as a single variable, so changing it in one affects all instances