python实现把二维列表变为一维列表的方法分析

c = [[1,2,3], [4,5,6], [7,8,9]]

> [n for a in c for n in a ]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

> result=[]
> for a in c:
 for n in a:
 result.append(n)
 result  #result的位置没有和第一个for对齐，所以结果不理想
[1]
[1, 2]
[1, 2, 3]
[1, 2, 3, 4]
[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5, 6]
[1, 2, 3, 4, 5, 6, 7]
[1, 2, 3, 4, 5, 6, 7, 8]
[1, 2, 3, 4, 5, 6, 7, 8, 9]

> sum(c,[])
[1, 2, 3, 4, 5, 6, 7, 8, 9]

>from itertools import chain
>list(chain(*vec))
[1,2, 3, 4, 5, 6, 7, 8, 9]
>from itertools import chain
>list(chain(*vec))
[1,2, 3, 4, 5, 6, 7, 8, 9]