请问python中列表如[1,2,3]怎么变成[1,1,1,2,2,2,3,3,3]?[face]m

请问python中列表如[1,2,3]怎么变成[1,1,1,2,2,2,3,3,3]?[face]monkey2:006.png[/face]

如下：

#!/usr/bin/python
# -*- coding: utf-8 -*-
import sys

list_a = [1,2,3]
list_b = []
for x in list_a:
    list_b.extend([x]*3)

print(str(list_b))