python splinter 处理弹出登陆窗口

Question

def login():
bwr.find_by_text(u"请登录").click()
sleep(2)
bwr.fill("userAccount", username)
sleep(2)
bwr.fill("password", passwd)
sleep(2)
bwr.find_by_id(u"btnLogin").click()
运行程序是报错：
splinter.exceptions.ElementDoesNotExist: no elements could be found with name "userAccount"

是不是弹出的窗口，是无法获取到html的元素名称的？怎么才能获取的？