Python 3-urllib，HTTP错误407：需要代理身份验证

import urllib.request as reqproxy = req.ProxyHandler({'http': r'http://username:password@url:port'})auth = req.HTTPBasicAuthHandler()opener = req.build_opener(proxy, auth, req.HTTPHandler)req.install_opener(opener)conn = req.urlopen('http://google.com')return_str = conn.read()