python使用递归实现一个分形图形

import turtle
def main():
    t = turtle.Turtle()
    t.hideturtle()
    t.speed(10)
    level = 12
    fract(t,-80,60,80,60,level)
def fract(t,x1,y1,x2,y2,level):
    newX = 0
    newY = 0
    if level == 0:
        drawLine(t,x1,y1,x2,y2)
    else:
        newX = (x1+x2)/2 + (y2-y1)/2
        newY = (y1+y2)/2 - (x2-x1)/2
        fract(t,x1,y1,newX,newY,level-1)
        fract(t,newX,newY,x2,y2,level-1)
def drawLine(t,x1,y1,x2,y2):
    t.up()
    t.goto(x1,y1)
    t.down()
    t.goto(x2,y2)

main()