http://www.cnblogs.com/coderzh/archive/2008/05/18/1201993.html
http://www.cnblogs.com/Anker/archive/2013/05/04/3059070.html
http://bbs.ancode.org/forum.php?mod=viewthread&tid=191
list = []
for i in range(0, X):
list.append(i)
for i in reversed(list):
print i