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

import turtle
import time

def 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()