How to think like a Computer Scientist: 课后习题第三章 12题

import turtle
import time

wn = turtle.Screen()
wn.bgcolor("green")
wn.title("yuxiangyang is testing!")

alex = turtle.Turtle()
alex.shape("turtle")
alex.color("navy blue")
alex.speed(0)
alex.penup()
alex.stamp()

for i in range(12):
alex.left(i*30)
alex.forward(100)
alex.stamp()
alex.forward(-100)
alex.right(i*30)

tess = turtle.Turtle()
tess.color("navy blue")
tess.pensize(4)
tess.speed(0)
tess.penup()

for i in range(12):
tess.left(i*30)
tess.forward(70)
tess.pendown()
tess.forward(15)
tess.penup()
tess.forward(-85)
tess.right(i*30)

time.sleep(10)
wn.bye()