pip install InsecurePlatformWarning: A true SSLContext object is not available.

Refer from https://www.phodal.com/blog/python-pip-openssl-issue/

在安装Python库的时候，遇到一些问题。虽然，还是遇到问题了:

Collecting PyMySQL
/Users/fdhuang/py27/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:79: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. For more information, see https://urllib3.readthedocs.org/en/latest/security.html#insecureplatformwarning.
  InsecurePlatformWarning
  Downloading PyMySQL-0.6.6-py2.py3-none-any.whl (66kB)
    100% |████████████████████████████████| 69kB 225kB/s
Installing collected packages: PyMySQL
Successfully installed PyMySQL-0.6.6

因为SSL的问题，urllib3需要pyopenssl。

最简单的方法是

 $ pip install pyopenssl ndg-httpsclient pyasn1

还需要安装libffi-dev，libssl-dev

1.Ubuntu下安装

sudo apt-get install libffi-dev libssl-dev