请大家给我看一下这个网站如何使用 python 模拟登陆？

工作任务突然下来了，好多，考虑了一下想使用python登陆获取数据，然后和本地系统数据对比做一下，但是我发现我使用requesrs模拟登陆竟然登陆失败，百思不得其解，只好向大家求助。
网址： http://61.178.81.162:8888/LQL_OA/login.aspx
因为保密的原因，账号和密码不能提供，请大家谅解，如果因为客观条件不能够提供代码，请达人提供一下思路，谢谢！

# -*- encoding: utf-8 -*-

import requests
from PIL import Image
from StringIO import StringIO
from lxml import etree
from lxml import *
import lxml.html
import urllib2
import lxml.html as H

txtUserName = ""
txtPassword = ""
yz = ''#验证码字符串

signin_url = "http://61.178.81.162:8888/LQL_OA/login.aspx"
login_url = "http://61.178.81.162:8888/LQL_OA/Index.aspx"
LoginCode_url ="http://61.178.81.162:8888/LQL_OA/LoginCode.aspx"
user_agent = "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)"
Referer = signin_url

__EVENTARGUMENT=''
__EVENTTARGET = 'lkbut_OK'
__VIEWSTATE = ''
__VIEWSTATEGENERATOR='17AE1282'


login = requests.get(signin_url)
doc = H.document_fromstring(login.content)
__VIEWSTATE = doc.xpath('//*[@id="__VIEWSTATE"]/@value')[0]

print __VIEWSTATE

#下载验证码图片
yz_LoginCode = requests.get(LoginCode_url)

im = Image.open(StringIO(yz_LoginCode.content))
im.show()
yz = input("Please input your Code:\n")

#登陆网页
headers = {"User-Agent": user_agent,'Referer': Referer,}


logininfo = {"txtUserName": txtUserName,
"txtPassword": txtPassword,
"yz": yz,
"__EVENTARGUMENT":__EVENTARGUMENT,
"__EVENTTARGET":__EVENTTARGET ,
"__VIEWSTATE":__VIEWSTATE,
"__VIEWSTATEGENERATOR":__VIEWSTATEGENERATOR,
}

liudong_session = requests.Session()
signin_req = liudong_session.post(signin_url,
data=logininfo,
headers=headers,
)

print signin_req.encoding


content = open('content.html', 'w')

content.write(signin_req.content.replace('/LQL_OA','http://61.178.81.162:8888/LQL_OA'))
content.close()

info = liudong_session.get(login_url)

info_content = open('info_content.html', 'w')
info_content.write(info.content.replace('/LQL_OA','http://61.178.81.162:8888/LQL_OA'))
info_content.close()