该drawTree功能不保留自称永远递归调用所以最终的陈述后 做 得到执行。当depth==处的递归调用LIMIT返回时，控制权将返回到上一个调用depth= = LIMIT-1。
这是代码的略微修改版本，并print引发了一些调用以帮助跟踪执行。
我还做了其他一些小的更改。我简化了SCALAR计算：0.5 * sqrt(2)==sqrt(0.5)，仅在乌龟实际绘制正方形时才放下笔。我还添加了一个turtle.mainloop()呼叫，以便在绘图完成后窗口保持打开状态。
from __future__ import print_function
import turtle
LIMIT = 3
SCALAR = 0.5 ** 0.5
INDENT = ' ' * 4
def drawTree(size, depth, branch):
print(INDENT * depth, branch, depth, 'start')
drawSquare(size)
if depth + 1 <= LIMIT:
t.left(90)
t.forward(size)
t.right(45)
drawTree(size * SCALAR, depth + 1, 'left ')
t.forward(size * SCALAR)
t.right(90)
drawTree(size * SCALAR, depth + 1, 'right')
t.left(90)
t.backward(size * SCALAR)
t.left(45)
t.backward(size)
t.right(90)
print(INDENT * depth, branch, depth, 'stop')
def drawSquare(sideLength):
t.down()
for i in range(4):
t.forward(sideLength)
t.left(90)
t.up()
t = turtle.Pen()
t.up()
t.goto(-100, -200)
drawTree(100.0, 0, 'root')
turtle.mainloop()
root 0 start
left 1 start
left 2 start
left 3 start
left 3 stop
right 3 start
right 3 stop
left 2 stop
right 2 start
left 3 start
left 3 stop
right 3 start
right 3 stop
right 2 stop
left 1 stop
right 1 start
left 2 start
left 3 start
left 3 stop
right 3 start
right 3 stop
left 2 stop
right 2 start
left 3 start
left 3 stop
right 3 start
right 3 stop
right 2 stop
right 1 stop
root 0 stop
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