python爬虫：用户名密码登录认证

需求：我们有时候想要访问一个网址(A:http://xxx.com/data.php)来获取自己想要的东西，访问后由于我们没有登录，系统为我们重定向到另一个网址(B:http://xxx.com/login.php)
我们已知一个账号admin/password
用python完成认证过程并请求A网址：

# -*-coding:UTF-8 -*-
import urllib
import urllib2
import re
import sys
import cookielib

def auth():
    headers = {
    "Accept":"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
    "Accept-Encoding":"gzip, deflate, sdch",
    "Accept-Language":"zh-CN,zh;q=0.8",
    "Connection":"keep-alive",
    "Host":"x.x.x.x",
    "User-Agent":"Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/49.0.2623.87 Safari/537.36"
    }
    url_A = "http://xxx.com/data.php"
    url_B = "http://xxx.com/login.php"
    data = {
    "username":"admin",
    "password":"password"
    }
    post_data = urllib.urlencode(data)
    cookieJar = cookielib.CookieJar()
    opener = urllib2.build_opener(urllib2.HTTPCookieProcessor(cookieJar))
    req = urllib2.Request(url_A,post_data,headers)
    result = opener.open(req)
    result = opener.open(url_A)
    print result.read()
    print "done"

if __name__ == "__main__":
    print "begin:"
    auth()