How to get all combinations of a list?

Question

I know that I can use itertools.permutation to get all permutations of size r.

But, for itertools.permutation([1,2,3,4],3) it will return (1,2,3) as well as (1,3,2).

1. I want to filter those repetitions (i.e obtain combinations)

2. Is there a simple way to get all permutations (of all lengths)?

3. How can I convert itertools.permutation() result to a regular list?

Answer 1

Use itertools.combinations and a simple loop to get combinations of all size.

combinations return an iterator so you've to pass it to list() to see it's content(or consume it).

>>> from itertools import combinations
>>> lis = [1, 2, 3, 4]
for i in xrange(1, len(lis) + 1):  #  xrange will return the values 1,2,3,4 in this loop
    print list(combinations(lis, i))
...     
[(1,), (2,), (3,), (4,)]
[(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]
[(1, 2, 3), (1, 2, 4), (1, 3, 4), (2, 3, 4)]
[(1,2,3,4)]