今天在服务器上搭建django开发环境的时候遇到了一问题，就是在python3下安装pymysql 出现以下问题
1.Failed cleaning build dir for cryptography
2.Command "/usr/bin/python3 -u -c "import setuptools, tokenize;__file__='/tmp/pip-build-yzhhq2aa/cryptography/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-399_hd6n-record/install-record.txt --single-version-externally-managed --compile --user --prefix=" failed with error code 1 in /tmp/pip-build-yzhhq2aa/cryptography/
原因就是系统缺少依赖包，一个命令装全解决：
sudo apt-get install python-dev python-pip libxml2-dev libxslt1-dev zlib1g-dev libffi-dev libssl-dev