permutations - fast & with low memory consumption?

[Gerard Flanagan]

Christian Meesters wrote:

> Hi,
>
> I'd like to hack a function which returns all possible permutations as lists
> (or tuples) of two from a given list. So far, I came up with this solution,
> but it turned out to be too slow for the given problem, because the list
> passed ("atomlist") can be some 1e5 items long:

<snip>
>
> Does anybody know a solution which consumes less memory and is possibly
> faster, perhaps using generator expressions? All my attempts so far failed.

No claims with respect to speed, but the kslice function here:

    http://gflanagan.net/site/python/utils/sequtils/

will give the 'k-subsets' which then need to be permuted -
alternatively Google.

Gerard