递归科赫雪花

import turtle,time
def koch(size,n):
    if n==0:
        turtle.fd(size)
    else:
        for angle in [0,60,-120,60]:
            turtle.left(angle)
            koch(size/3,n-1)
def main():
    turtle.setup(600,600)
    turtle.penup()
    turtle.goto(-200,100)
    turtle.pendown()
    turtle.pensize(2)
    level=3
    koch(400,level)
    turtle.right(120)
    koch(400,level)
    turtle.right(120)
    koch(400, level)
    # turtle.hideturtle()
    time.sleep(3)
    turtle.done
main()