selenium启动PhantomJS错误

from selenium import webdriver
browser = webdriver.PhantomJS(executable_path="D:\PhantomJS\phantomjs-2.1.1-windows\bin\phantomjs")

报错“Unable to start phantomjs with ghostdriver.”

加上r就ok了

from selenium import webdriver
browser = webdriver.PhantomJS(executable_path=r"D:\PhantomJS\phantomjs-2.1.1-windows\bin\phantomjs")