How to think like a Computer Scientist: 课后习题第十八章1

import turtleimport timedef koch(t, order, size):    if order == 0:        t.forward(size)    else:        for angle in [60, -120, 60, 0]:            koch(t,order - 1, size/3)            t.left(angle)wn = turtle.Screen()wn.bgcolor("green")wn.title("yuxiangyang is testing!")tess = turtle.Turtle()tess.color("navy blue")tess.pensize(4)tess.penup()tess.forward(-100)tess.left(90)tess.forward(100)tess.right(90)tess.pendown()for i in range(3):    koch(tess, 2, 300)    tess.right(120)time.sleep(10)wn.bye()