How to get all partitions of a set?

For example, I have array [1, 2, 3]. I need to get [[1], [2], [3]], [[1], [2, 3]], [[2], [1,3]], [[3], [1, 2]], [[1, 2, 3]].

Now, I wrote this code:

def neclusters(S, K):for splits in itertools.combinations(range(len(S)), K):yield np.split(S, 1 + np.array(splits))

But that code don't return [[2],[1,3]].

I could take all permutations of the original set and run this code on them. But can this be made easier?

I wrote this one for fun:

def partition(a_list):yield [[x] for x in a_list]   for i in range(1, len(a_list) + 1):_l = a_list[:]yield [_l.pop(i-1), _l]yield a_listmy_list = [1, 2, 3]
print list(partition(my_list))#orfor p in partition(my_list):print p