在python下执行pip install，报错：

$ ./pip install pyopenssl ndg-httpsclient pyasn1

Collecting pyopenssl

Could not fetch URL https://pypi.python.org/simple/pyopenssl/: There was a problem confirming the ssl certificate: [Errno 1] _ssl.c:499: error:1407742E:SSL routines:SSL23_GET_SERVER_H ELLO:tlsv1 alert protocol version – skipping

C:\Python27\lib\site-packages\pip-9.0.1-py2.7.egg\pip\_vendor\requests\packages\urllib3\util\ssl_.py:318: SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name In dication) extension to TLS is not available on this platform. This may cause the server to present an incorrect TLS certificate, which can cause validation failures. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#snimissingwarning.

SNIMissingWarning

C:\Python27\lib\site-packages\pip-9.0.1-py