Очистка tkinter canvas

from tkinter import *
from tkinter import messagebox
import time
import random

tk = Tk()
app_running = True
size_canvas_x = 700
size_canvas_y = 500
menu_x = 250
menu_y = 50
canvas_elements = []


def click_canvas(event):
    mouse_x = canvas.winfo_pointerx() - canvas.winfo_rootx()
    mouse_y = canvas.winfo_pointery() - canvas.winfo_rooty()
    if 0 <= mouse_x <= size_canvas_x and 0 <= mouse_y <= size_canvas_y:
        x = mouse_x
        y = mouse_y
        rgb_color = (random.randint(0, 255), random.randint(0, 255), random.randint(0, 255))
        canvas_elements.append(canvas.create_rectangle(x, y, x + 50, y + 50, fill=_from_rgb(rgb_color)))


def _from_rgb(rgb):
    """translates an rgb tuple of int to a tkinter friendly color code
    """
    return "#%02x%02x%02x" % rgb


def test_canvas_clear():
    if canvas_elements:
        cid = canvas_elements.pop()
        canvas.delete(cid)


def test_canvas():
    x = random.randint(0, size_canvas_x)
    y = random.randint(0, size_canvas_y)
    rgb_color = (random.randint(0, 255), random.randint(0, 255), random.randint(0, 255))
    canvas_elements.append(canvas.create_rectangle(x, y, x+50, y+50, fill=_from_rgb(rgb_color)))


def on_closing():
    global app_running
    if messagebox.askokcancel("Выход из игры", "Хотите выйти из игры?"):
        app_running = False
        tk.destroy()


tk.protocol("WM_DELETE_WINDOW", on_closing)
tk.title("Test")
tk.resizable(0, 0)
tk.wm_attributes("-topmost", 1)
canvas = Canvas(tk, width=size_canvas_x + menu_x, height=size_canvas_y + menu_y, bd=0,
                highlightthickness=0)
canvas.create_rectangle(0, 0, size_canvas_x, size_canvas_y, fill="white")
canvas.pack()
tk.update()

button1 = Button(text="Test", command=test_canvas)
button1.place(x=size_canvas_x+10, y=20, width=230, height=50)

button2 = Button(text="Clear", command=test_canvas_clear)
button2.place(x=size_canvas_x+10, y=90, width=230, height=50)

canvas.bind_all("<Button-1>", click_canvas)  # ЛКМ
canvas.bind_all("<Button-3>", click_canvas)  # ПКМ

while app_running:
    if app_running:
        tk.update_idletasks()
        tk.update()
    time.sleep(0.005)