一些教程：
https://docs.python.org/2.7/howto/logging.html#logging-advanced-tutorial
http://kenby.iteye.com/blog/1162698
http://www.cnblogs.com/Bob-FD/p/3326713.html
http://www.360doc.com/content/12/1123/13/9369336_249734290.shtml
