例子1：递归实现嵌套列表求和
#encoding=utf-8
a=[[1,2,3],
[4,5,6],
[7,8,9]]
def listsum(L):
result=0
for i in L:
if isinstance(i,list):
result +=listsum(i)
else:
result += i
return result
print listsum(a)
结果：
未完待续