I want to change my desktop by writing a python program,can somebody help me ?thanks so much!

i know this can do
import ctypes
import Image
# -*- coding: cp936 -*-

STOREDIR = './img'

def setWallpaperFromBMP(imagepath):
SPI_SETDESKWALLPAPER = 20 # According to http://support.microsoft.com/default.aspx?scid=97142
ctypes.windll.user32.SystemParametersInfoA(SPI_SETDESKWALLPAPER, 0, imagepath , 0) #SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE

def setWallPaper(imagePath):
"""Given a path to an image, convert it to bmp and set it as wallpaper"""
bmpImage = Image.open(imagePath)
newPath = STOREDIR + 'mywallpaper.bmp'
bmpImage.save(newPath, "BMP")
setWallpaperFromBMP(newPath)

filename="./girl6.jpg"
setWallPaper(filename)

but it seems not so good,somebody who know how to get the point of iactivedesktop?