安装系统：
CentOS，redHat
步骤：
1.安装pip，已安装请忽视
wget --no-check-certificate https://github.com/pypa/pip/archive/1.5.5.tar.gz tar zvxf 1.5.5.tar.gz cd pip-1.5.5/ python setup.py install
2.安装依赖库，已安装请忽视
yum install libxml2
yum install libxslt-devel
3. 安装lxml
pip install lxml
问题解决：
1. 处理 error: command 'gcc' failed with exit status 1
yum install gcc python-devel
或者
yum install gcc libffi-devel python-devel openssl-devel
2. 处理 from setuptools import setup, find_packages ImportError: No module named set
wget http://peak.telecommunity.com/dist/ez_setup.py python ez_setup.py
