python urllib2访问https报错CERTIFICATE_VERIFY_FAILED

近期使用了一段开源的python脚本，脚本中使用了urllib2来作为HTTP客户端，在访问https站点时报下面的错误：

First request to SP failed: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] cert
ificate verify failed (_ssl.c:726)>

代码如下：

    # create a cookie jar and cookie handler
    cookie_jar = cookielib.LWPCookieJar()
    cookie_handler = urllib2.HTTPCookieProcessor(cookie_jar)

    # need an instance of HTTPS handler to do HTTPS
    httpsHandler = urllib2.HTTPSHandler(debuglevel = 0)
    if debug:
        httpsHandler.set_http_debuglevel(1)

    # create the base opener object
    opener = urllib2.build_opener(cookie_handler, httpsHandler)

    # headers needed to indicate to the SP an ECP request
    headers = {
                'Accept' : 'text/html; application/vnd.paos+xml',
                'PAOS'   : 'ver="urn:liberty:paos:2003-08";"urn:oasis:names:tc:SAML:2.0:profiles:SSO:ecp"'
                }

    # request target from SP 
    request = urllib2.Request(url=sp_target,headers=headers)

    try:
        response = opener.open(request)
    except Exception, e:
        print >>sys.stderr, "First request to SP failed: %s" % e
        sys.exit(1)

最终通过设置ssl unverified的context解决。

import ssl
ssl._create_default_https_context = ssl._create_unverified_context