On Wed, Aug 17, 2011 at 9:09 AM, Stan Schymanski <schym...@gmail.com> wrote:
> Dear all,
>
> This has been driving me mad. According to the python documentation,
> you can modify a copy of a list without modifying the original using
> the following code:
>
> sage: L = []
> sage: M = L[:] # create a copy
> sage: # modify L only
> sage: L.append(1)
> sage: M
> []
>
> Now, I want to do the same with a nested list, but I do not manage to
> unlink the two. See the example below, where I also tried copy(L) to
> no avail. I hope that someone can help. Thanks already!
A "copy" of a list is a new list containing exactly the same elements
as the original list. It sounds like what you want here is
sage: import copy
sage: L = [range(k) for k in range(5)]
sage: M = copy.deepcopy(L)
sage: M[0].append('something')
sage: M
[['something'], [0], [0, 1], [0, 1, 2], [0, 1, 2, 3]]
sage: L
[[], [0], [0, 1], [0, 1, 2], [0, 1, 2, 3]]
- Robert
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