python 读取系统环境变量的代码

将开发过程常用的内容收藏起来，如下代码段是关于python 读取系统环境变量的代码，应该是对码农们有些用处。

#!/usr/bin/env python
#
# [SNIPPET_NAME: Read an environmental variable]
# [SNIPPET_CATEGORIES: os]
# [SNIPPET_DESCRIPTION: Read and print a given environmental variable]
# [SNIPPET_AUTHOR: Jono Bacon <jono@ubuntu.com>]
# [SNIPPET_LICENSE: GPL]

import os

# display the USERNAME environmental variable
print os.getenv('USERNAME')