Python特殊语法:filter、map、reduce、lambda
https://www.cnblogs.com/longdouhzt/archive/2012/05/19/2508844.html
https://www.cnblogs.com/XXCXY/p/5180245.html
Python filter() 函数
http://www.runoob.com/python/python-func-filter.html
Python xrange与range的区别
http://www.nowamagic.net/academy/detail/1302446