一个关于python的小小问题

Python怎么用turtle生成一个随机点，当点击它的时候继续生成下一个。（Python对函数理解不深想用onclick()发现不好使）

import random
import turtle

turtle.getscreen().bgcolor("pink")

# point size
R = 20

# set speed (optional)
turtle.speed("fastest")

# screen size for generate point
size = turtle.getscreen().screensize()
W = size[0]
H = size[1]

# save position
X = 0
Y = 0


def draw_rand_circle():
    global W, H, X, Y
    # generate point in screen
    X = random.randrange(-W+R, W-R)
    Y = random.randrange(-H, H-2*R)

    # draw circle
    turtle.pencolor("pink")
    turtle.goto(X, Y)
    turtle.color("yellow", "green")
    turtle.begin_fill()
    turtle.circle(R)
    turtle.end_fill()

def redraw(a, b):
    global X, Y
    # is click in the circle?
    if X-R < a < X+R and Y < b < Y+2*R:
        draw_rand_circle()

draw_rand_circle()
turtle.getscreen().onclick(redraw)

turtle.mainloop()