Slice a list of lists?

[Terry Reedy]

On 9/8/2010 2:55 PM, Jonno wrote:
> I know that I can index into a list of lists like this:
> a=[[1,2,3],[4,5,6],[7,8,9]]
> a[0][2]=3
> a[2][0]=7
>
> but when I try to use fancy indexing to select the first item in each
> list I get:
> a[0][:]=[1,2,3]
> a[:][0]=[1,2,3]
>
> Why is this and is there a way to select [1,4,7]?

You are trying to look at a list of lists as an array and have 
discovered where the asymmetry of the former makes the two 
non-equivalent. To slice multi-dimensional arrays any which way, you 
need an appropriate package, such as numpy.

-- 
Terry Jan Reedy