用Python画图，缓解乏味的学习.....（下）

# 绘制分形树******************************************************************************
import turtle
def draw_branch(branch_length):
    '''
        绘制分形树
    '''
    if branch_length > 5:
        #    绘制右侧树枝
        turtle.forward(branch_length)
        print("向前：", branch_length)
        turtle.right(20)
        print("右转：20度")
        draw_branch(branch_length - 15)
        # 绘制左侧树枝
        turtle.left(40)
        print("左转：40度")
        draw_branch(branch_length - 15)
        # 返回之前的树枝
        turtle.right(20)
        print("右转：20度")
        turtle.backward(branch_length)
        print("向后：", branch_length)
def main():
    '''
       主函数
    '''
    turtle.speed(0.5)
    turtle.pensize(3)
    turtle.left(90)
    turtle.color('green')
    turtle.penup()
    turtle.backward(150)
    turtle.pendown()
    turtle.bgcolor("black")
    draw_branch(100)
    turtle.exitonclick()
if __name__ == "__main__":
    main()

# 彩虹线绘制案例***************************************************************************
import turtle as t
from random import randint as rint
t.shape("turtle")
t.pensize(5)
t.colormode(255)
t.bgcolor("black")
t.tracer(False)
for x in range(700):
    t.color(rint(0,255),rint(0,255),rint(0,255))
    t.circle(2*(1+x/4),5)
    t.speed(0)
    t.tracer(True)
t.exitonclick()