Automagically change wallpaper

ChangeWallpaper.py

sub = "widescreenwallpaper";
fileName = "kwp";

changeCommands = {"gnome":"gsettings set org.gnome.desktop.background picture-uri \"file://$URI\"","darwin":"osascript -e 'tell application \"Finder\" to set desktop picture to POSIX file \"$URI\"'"}

import urllib2;
import json;
import os;
import re;
import platform;

osType = platform.system();
wm = "";
if 'DESKTOP_SESSION' in os.environ:
    wm = os.environ['DESKTOP_SESSION'];

def getData(subreddit):
    raw = urllib2.urlopen("https://www.reddit.com/r/%s/top.json?t=day&limit=1" % (subreddit)).read();
    parsed = json.loads(raw)['data'];
    return parsed['children'][0]['data']['preview']['images'][0]['source'];

def downloadImg(url, path):
    with open(path,'wb+') as f:
        f.write(urllib2.urlopen(url).read());

def changeBackground(path):
    cmdType = wm;
    if osType == "Darwin":
        cmdType = "darwin";
    return os.system(changeCommands[cmdType].replace("$URI",path))

def getExtension(url):
    match = re.search('\.(.{3,4})\?', url);
    if match:
        return match.group(1);
    return False;

if wm in changeCommands or osType == "Darwin":
    data = getData(sub);
    imgPath = ("%s/Pictures/%s.%s" % (os.environ['HOME'],fileName,getExtension(data['url'])));
    downloadImg(data['url'], imgPath);
    changeBackground(imgPath);
else:
    print "Your WM (%s) is not supported." % (wm);