python-海龟画图

import turtle as t

t.setup(1000,800)

def draw_tree(branch_length):
    if branch_length>1:
        t.right(20)
        t.forward(branch_length)
        draw_tree(branch_length-6)
        t.backward(branch_length)
        t.left(40)
        t.forward(branch_length)
        draw_tree(branch_length-6)
        t.backward(branch_length)
        t.right(20)
    else:
     return 0
        
t.left(90)
t.penup()
t.goto(0,-20)
t.pendown()
t.fd(100)
draw_tree(48)