selenium如何定位鼠標懸停才顯示的按鈕

# coding:utf-8
from selenium import webdriver
from selenium.webdriver.common.action_chains import ActionChains

driver = webdriver.Firefox()
driver.get("http://xxxxxxx.com")
# 定位鼠標懸停才顯示的“退出登錄”按鈕
mouse = self.driver.find_element_by_xpath("//*[contains(text(),'hello')]")
ActionChains(self.driver).move_to_element(mouse).perform()
self.driver.find_element_by_xpath("//*[contains(text(),'退出登錄')]").click()