在CentOS 6.x上，默认自带的Python是2.6.x版本，这个版本的Python有点老了，比如“collections.OrderedDict”就是2.7才有的，而且著名的Python Web框架Django的新版（如：1.7）就不支持Python2.6，最低要求是2.7了。而一些公司或者共有云上的服务器就是使用CentOS6.x，所以也就有了升级Python到2.7的需求。
升级Python之前，需要先安装一些工具和软件库，否则后面安装Python或pip时可能出错。
Python2.7通过源码安装，python可行执行程序默认是安装在/usr/local/bin/，一般来在$PATH中，/usr/local/bin是优先使用的（如果不是，需要自己设置一下PATH环境变量）。
在安装完python后，还需要安装easy_install和pip这两个最常用工具。
整个安装过程，我总结过如下一个Shell脚本（以安装Python2.7.8为例，以root权限运行），供参考：
https://github.com/smilejay/shell/blob/master/sh2014/install_py27_on_centos.sh
#!/bin/bash
# a script to install python 2.7 on CentOS 6.x system.
# CentOS 6.x has python 2.6 by default, while some software (e.g. django1.7)
# need python 2.7.
# install some necessary tools & libs
echo "install some necessary tools & libs"
yum groupinstall "Development tools"
yum install openssl-devel zlib-devel ncurses-devel bzip2-devel readline-devel
yum install libtool-ltdl-devel sqlite-devel tk-devel tcl-devel
sleep 5
# download and install python
version='2.7.8'
python_url="https://www.python.org/ftp/python/$version/Python-${version}.tgz"
# check current python version
echo "before installation, your python version is: $(python -V &2>1)"
python -V 2>&1 | grep "$version"
if [ $? -eq 0 ]; then
echo "current version is the same as this installation."
echo "Quit as no need to install."
exit 0
fi
echo "download/build/install your python"
cd /tmp
wget $python_url
tar -zxf Python-${version}.tgz
cd Python-${version}
./configure
make -j 4
make install
sleep 5
echo "check your installed python"
python -V 2>&1 | grep "$version"
if [ $? -ne 0 ]; then
echo "python -V is not your installed version"
/usr/local/bin/python -V 2>&1 | grep "$version"
if [ $? -ne 0 ]; then
echo "installation failed. use '/usr/local/bin/python -V' to have a check"
fi
exit 1
fi
sleep 5
# install setuptools
echo "install setuptools"
wget https://bitbucket.org/pypa/setuptools/raw/bootstrap/ez_setup.py
python ez_setup.py
# check easy_install version
easy_install --version
sleep 5
# install pip for the new python
echo "install pip for the new python"
easy_install pip
# check pip version
pip -V
echo "Finished. Well done!"
echo "If 'python -V' still shows the old version, you may need to re-login."
echo "And/or set /usr/local/bin in the front of your PATH environment variable."
echo "-------------------------"
