login Quora programmatically but got HTTP Error 500

gistfile1.py

# login the Quora and get notifications with unofficial API (http://www.quora.com/Edmond-Lau/Edmond-Laus-Posts/Quora-Extension-API)
# tpeng <[email protected]> 2013/1/7

# some references
# https://gist.github.com/2341517
# http://www.ruby-doc.org/gems/docs/q/quora-client-0.1.2/Quora/Auth.html
# http://stackoverflow.com/questions/10616449/how-to-programmatically-log-in-to-quora-by-java-code

import cookielib
import json
import re
import urllib

import urllib2

class Quora(object):
    def __init__(self):
        self.cj = cookielib.LWPCookieJar()
        cookie_support = urllib2.HTTPCookieProcessor(self.cj)
        opener = urllib2.build_opener(cookie_support, urllib2.HTTPHandler(debuglevel=1))
        urllib2.install_opener(opener)

    def login(self, email, pwd):
        url = 'http://www.quora.com/login'
        text = urllib2.urlopen(url).read()
        p_formkey = re.compile(r'formkey:\s+\"([a-z0-9]+)\"', re.I | re.M)
        formkey = re.search(p_formkey, text).group(1)

        p_window_id = re.compile(r'windowId\s+=\s+\"([a-z0-9-]+)\"', re.I | re.M)
        window_id = re.search(p_window_id, text).group(1)

        p_live = re.compile(r'live:(\w+):cls:a\.app\.view\.login', re.I | re.M)
        p_vconjson = re.compile(r'InlineLoginBase:(\w+)\"', re.I | re.M)

        vconjson = {'cls':'a.app.view.login', 'InlineLogin': re.search(p_vconjson, text).group(1),
                    'live' : re.search(p_live, text).group(1)}

#        username = urllib.quote(username)
#        pwd = urllib.quote(pwd)

        auth_data = {'args' : [],
                     'kwargs':
                         {'email' : email, 'password' : pwd}}

        data = {'json' : auth_data,
                'window_id' : window_id,
                'formkey': formkey,
                '__vcon_json': json.dumps(vconjson),
                '__vcon_method' : 'do_login',
                'js_init': '{}'}

        headers = {'User-Agent': 'Mozilla/5.0 (X11; Linux i686; rv:8.0) Gecko/20100101 Firefox/8.0',
#                   'Referer' : 'http://www.quora.com/login/',
#                   'X-Requested-With' : "XMLHttpRequest",
#                   'Accept' : "application/json, text/javascript, */*",
        }

        req = urllib2.Request(
            url='http://www.quora.com/webnode2/server_call_POST/',
            data=urllib.urlencode(data),
            headers=headers
        )

        text = urllib2.urlopen(req).read()
        print text

    def get_notifications(self):
        url = 'http://api.quora.com/api/logged_in_user?fields=notifs,inbox'
        result = urllib2.urlopen(url)
        text = result.read()
        print text
        return text

if __name__ == '__main__':
    q = Quora()
    q.login('[email protected]', 'xxx')

I tried using mechanize, and got the same HTTP 500 error. Did you figure out why Quora seems unhappy about bots logging in to the site?