selenium调用JavaScript控制浏览器滚动条

# coding=utf-8
from selenium import webdriver
from time import sleep

dr = webdriver.Firefox()
dr.get("http://www.baidu.com")

dr.find_element_by_id('kw').send_keys('selenium')
dr.find_element_by_id('su').click()
sleep(2)

#数值足够大时滑动到底部，单位像素
js = "var q=document.documentElement.scrollTop=9999999"  
dr.execute_script(js)  #调用js
sleep(2)

js1 = "var q=document.documentElement.scrollTop=0"   #等于0时在顶部
dr.execute_script(js1)
sleep(2)

js2 = "var q=document.documentElement.scrollTop=500"   #从顶部往下移动500像素
dr.execute_script(js2)
sleep(2)

调用js方法：execute_scrip()