Python Twisted：SSL例程,ssl3_get_server_certificate错误

我正在使用 http://twistedmatrix.com/documents/current/core/howto/ssl.html中的check_server_certificate.py代码示例
?????????????????????????????????????????????????????????????????????????????????为了从公共服务器获取证书.

from __future__ import print_function
import sys
from twisted.internet import defer,endpoints,protocol,ssl,task,error

def main(reactor,host,port=443):
    options = ssl.optionsForClientTLS(hostname=host.decode('utf-8'))
    port = int(port)

    class ShowCertificate(protocol.Protocol):
        def connectionMade(self):
            self.transport.write(b"GET / HTTP/1.0rnrn")
            self.done = defer.Deferred()
        def dataReceived(self,data):
            certificate = ssl.Certificate(self.transport.getPeerCertificate())
            print("OK:",certificate)
            self.transport.abortConnection()
        def connectionLost(self,reason):
            print("Lost.")
            if not reason.check(error.ConnectionClosed):
                print("BAD:",reason.value)
            self.done.callback(None)

    return endpoints.connectProtocol(
        endpoints.SSL4ClientEndpoint(reactor,port,options),ShowCertificate()
    ).addCallback(lambda protocol: protocol.done)

task.react(main,sys.argv[1:])

从PyPI安装了必要的“service_identity”和“idna”软件包后仍然出现此错误：

$python check_server_certificate.py www.twistedmatrix.com
Lost.
BAD: [('SSL routines','ssl3_get_server_certificate','certificate verify failed')]

有任何想法吗？

SSL_CERT_FILE = "$(python -m certifi)" 
python check_server_certificate.py www.twistedmatrix.com