http://blog.chinaunix.net/uid-23500957-id-3990473.html

http://www.cnblogs.com/vamei/archive/2012/07/10/2582787.html

http://www.cnblogs.com/tqsummer/archive/2010/12/27/1917927.html

http://blog.csdn.net/alvine008/article/details/43410079

python-->基础-->004-->迭代器