以下代码仅作演示：

#!/usr/bin/env python
# -*- coding: UTF-8 -*-
from selenium import webdriver
from selenium.webdriver.support.ui import WebDriverWait

browser = webdriver.Firefox()
browser.set_page_load_timeout(20)   # 防止页面加载个没完
browser.get('https://www.zhihu.com/')

browser.find_element_by_class_name("js-signin").click()   # 点击登录按钮，一般网站该步可省略

email = browser.find_element_by_xpath("//input[@name='email']")
email.clear()
email.send_keys("test@test.com")
password = browser.find_element_by_xpath("//input[@name='password']")
password.clear()
password.send_keys("12345678")
form = browser.find_element_by_xpath("//form[@class='zu-side-login-box']")
form.submit()

somedom = WebDriverWait(browser, 60).until(lambda brow: brow.find_elements_by_class_name("zu-main-feed-con"))[0]

html = somedom.find_element_by_xpath("//*").get_attribute("outerHTML")
print html
browser.quit()