How program a particilar algorithm ?

[Hans Nowak]

Michel Bonnifait wrote:
> 
> Hello,
> I think my question is more on programming than specifically on programming
> with Python.
> I want to generate all possible lists with elements from another one. For
> example, from a list like [1,2,3,4] i want to program an algorithm which
> will give this result
> [[1,2],[1,3],[1,4],[1,2,3],[1,2,4],[1,3,4],[1,2,3,4],[2,3],[2,4],[2,3,4],[3,
> 4]]
> It's seems to me it should be a recursive programming answer but i can't
> find it.
> thanks in advance for your help !

This code seems to work:

def perms(lst):
    if len(lst) == 1: 
        return [lst]
    # return first element of list, combined with perms
    head, tail = lst[0], lst[1:]
    ptail = perms(tail)
    phead = [[head]+p for p in ptail]
    return phead + ptail + perms([head])

lst = [1, 2, 3, 4]

for p in perms(lst):
    print p


This question has been asked on the ng before, so you might be able to
find
other (better?) replies by doing a google search or so.

HTH,

--Hans