web自动化---下拉框及双击操作

from selenium import  webdriver
import time
from selenium.webdriver import ActionChains

url = "https://testpages.herokuapp.com/styled/basic-html-form-test.html"
driver = webdriver.Chrome()
driver.implicitly_wait(10)
a=ActionChains(driver)
driver.get(url)
driver.find_element('xpath','//input[@value="cb1"]').click()#单选
time.sleep(5)
b=driver.find_element('xpath','//input[@value="cb2"]')
a.double_click(b)#双击
driver.find_element('xpath','//option[@value="dd6"]').click()#下拉框