python:代碼訪問weixin.sogou.com的時(shí)候會(huì)出現(xiàn)驗(yàn)證碼，但是瀏覽器打開就不會(huì)

自己寫了個(gè)程序抓取weixin.sogou.com的數(shù)據(jù)，時(shí)不時(shí)就出現(xiàn)驗(yàn)證碼。
但是，當(dāng)我使用瀏覽器打開weixin.sogou.com的時(shí)候，并沒有出現(xiàn)驗(yàn)證碼。
難道搜狗不是根據(jù)IP來(lái)判斷的嗎？
代碼：

def __weixin_search(self, keyword, cur_page, start_date, end_date, timeout=30):
        html = None
        while True:
            try:
                if self.__cookie is None:
                    self.__set_cookie(timeout=timeout)
                if isinstance(keyword, types.UnicodeType):
                    keyword = keyword.encode('utf-8')
                url = "http://weixin.sogou.com/weixin?type=2&s_from=input&ie=utf8&_sug_=n&_sug_type_=&query="
                url += urllib2.quote(keyword)
                headers = {
                    "User-Agent": random.choice(USER_AGENTS),# 隨機(jī)
                    "Accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8",
                    "Accept-Language": "zh-CN,zh;q=0.8",
                    "Accept-Encoding": "gzip, deflate, sdch",
                    "DNT": "1",
                    "Connection": "keep-alive",
                    "Cookie": self.__cookie
                }
                r = requests.get(url=url, headers=headers, timeout=timeout)
                html = r.text.encode('ISO-8859-1')
                if html is None or html.find(u'seccodeInput') is not -1:
                    # 判斷是否出現(xiàn)驗(yàn)證碼，出現(xiàn)的時(shí)候，有個(gè)切換IP的函數(shù)會(huì)執(zhí)行
                    self.__cookie = None
                    time.sleep(1)
                else:
                    t = HTMLParser.HTMLParser()
                    return t.unescape(html)
            except Exception as ex:
                #print_msg(msg=traceback.format_exc(), save_to_log=True)
                pass