code: def login(self, email, password, captcha=None):
          
          data = {'email': email, 'password': password,
                  'remember_me': 'true'}
          if captcha is not None:
              data['captcha'] = captcha
          r = self._session.post(Login_URL, data=data)
          j = r.json()
          code = int(j['r'])
          message = j['msg']
          cookies_str = json.dumps(self._session.cookies.get_dict()) \
              if code == 0 else ''
          return code, message, cookies_str
docs: 登陆知乎.
  
          :param str email: 邮箱
          :param str password: 密码
          :param str captcha: 验证码, 默认为None，表示不提交验证码
          :return:
              ======== ======== ============== ====================
              元素序号 元素类型 意义           说明
              ======== ======== ============== ====================
              0        int      是否成功       0为成功，1为失败
              1        str      失败原因       登录成功则为空字符串
              2        str       cookies字符串 登录失败则为空字符串
              ======== ======== ============== ====================
  
          :rtype: (int, str, str)