2D List

[Ian Kelly]

On Mon, Oct 11, 2010 at 1:44 PM, Tom Pacheco <tomslists at netp.org> wrote:

> your creating a 1d list
>
> this creates a 2d list
> a=[[[]]*5
>
>
> >>> [0]*5
> [0, 0, 0, 0, 0]
> >>> [[]]*5
> [[], [], [], [], []]
>

Don't do this.  This actually just creates a list containing the same empty
list 5 times:

>>> a = [[]] * 5
>>> a
[[], [], [], [], []]
>>> a[0].append(1)
>>> a
[[1], [1], [1], [1], [1]]
>>> a[1][0] = 2
>>> a
[[2], [2], [2], [2], [2]]

Chris gave a correct way to create a list of lists, using a list
comprehension.

Cheers,
Ian
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