python基础
http://www.cnblogs.com/mao-19/p/5867238.html
【Python】Python中如何实现for循环step=2，step=-2
http://blog.****.net/henryghx/article/details/12408597
http://www.cnblogs.com/mao-19/p/5867238.html
【Python】Python中如何实现for循环step=2，step=-2
http://blog.****.net/henryghx/article/details/12408597