python递归的例子

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)