paint.py

from tkinter import *
import random

root = Tk()

colors = ['navy', 'slate blue', 'lime green',
          'purple', 'firebrick', 'salmon',
          'slate gray']

# Exit button
def exit():
    root.destroy()

b1 = Button(root, text="Exit", command=exit)
b1.pack(side=BOTTOM,padx=20)


def clear():
    canvas.delete('all')

clear_button = Button(root, text="Clear", command=clear)
clear_button.pack(side=BOTTOM, padx=20)


def undo():
    global MEMORY
    global CLICK_COUNTS

    number_to_delete = CLICK_COUNTS[-1]
    for index in range(-number_to_delete, 0):
        canvas.delete(MEMORY[index])
        del MEMORY[index]

    del CLICK_COUNTS[-1]
    
    
undo_button = Button(root, text="Undo", command=undo)
undo_button.pack(side=BOTTOM)



canvas = Canvas(root, width=400, height=400)
canvas.pack()

def get_pointer(event=None):
    x = root.winfo_pointerx() - root.winfo_rootx()
    y = root.winfo_pointery() - root.winfo_rooty()
    print("You clicked at {}, {}".format(x, y))
    return x, y

MEMORY = []
def draw_rectangle(x, y):
    shape = canvas.create_rectangle(
        x, y, x + 10, y + 10,
        fill=random.choice(colors))
    
    global MEMORY
    MEMORY.append(shape)


LOOP = True
CLICK_COUNTS = []
def draw(event=None):
    x, y = get_pointer()
    draw_rectangle(x, y)
    
    global CLICK_COUNTS
    CLICK_COUNTS[-1] = CLICK_COUNTS[-1] + 1

    global LOOP
    if LOOP:
        root.after(1, draw)

def start_draw(event=None):
    global CLICK_COUNTS
    CLICK_COUNTS.append(0)
    
    global LOOP
    LOOP = True
    draw()



def stop_draw(event=None):
    global LOOP
    LOOP = False

    global MEMORY
    print("There are {} shapes".format(len(MEMORY)))


canvas.bind('<Button-1>', start_draw)
canvas.bind('<ButtonRelease-1>', stop_draw)

root.mainloop()