click_and_hold()指的是按住鼠标左键在源元素上，点击并且不释放，就以百度搜索为案例
release()值鼠标释放，在调用click_and_hold()方法的时候，鼠标并没有释放
#coding:utf-8
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.common.action_chains import ActionChains
import time as t
driver=webdriver.Firefox()
driver.maximize_window()
driver.get('http://www.baidu.com')
driver.find_element_by_id('kw').send_keys('webdriver')
hold=driver.find_element_by_id('su')
ActionChains(driver).click_and_hold(hold).perform()
driver.quit()
#coding:utf-8
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.common.action_chains import ActionChains
import time as t
driver=webdriver.Firefox()
driver.maximize_window()
driver.get('http://www.baidu.com')
driver.find_element_by_id('kw').send_keys('webdriver')
hold=driver.find_element_by_id('su')
ActionChains(driver).click_and_hold(hold).release()
t.sleep(6)
driver.quit()
