Python - Tkinter - move balls

import tkinter as tk

# --- classes ---

class Ball:

    def __init__(self, canvas, color, x, y):
        self.canvas = canvas
        self.id = canvas.create_oval(x, y, x+25, y+25, fill=color)

    def update(self):
        self.canvas.move(self.id, 1, 1)

# --- functions ---

def update():
    ball1.update()
    ball2.update()
    root.after(100, update) # next execution (again) after 100ms

# --- main ---

root = tk.Tk()
canvas = tk.Canvas(root, width=500, height=400, bd=0, highlightthickness=0)
canvas.pack()

ball1 = Ball(canvas, 'red', 10, 10)
ball2 = Ball(canvas, 'blue', 100, 10)

#update() # first execution immediately
root.after(100, update) # or first execution after 100ms

root.mainloop() # start tkinter engine