This is just an example, but given the following model:

class Foo(models.model):
    bar = models.IntegerField()

    def __str__(self):
        return  str(self.bar)

    def __unicode__(self):
        return str(self.bar)

And the following QuerySet object:

foobar = Foo.objects.filter(bar__lt=20).distinct()

(meaning, a set of unique Foo models with bar <= 20), how can I generate all possible subsets of foobar? Ideally, I'd like to further limit the subsets so that, for each subset x of foobar, the sum of all f.bar in x (where f is a model of type Foo) is between some maximum and minimum value.

So, for example, given the following instance of foobar:

>> print foobar
[<Foo: 5>, <Foo: 10>, <Foo: 15>]

And min=5, max=25, I'd like to build an object (preferably a QuerySet, but possibly a list) that looks like this:

[[<Foo: 5>], [<Foo: 10>], [<Foo: 15>], [<Foo: 5>, <Foo: 10>],
 [<Foo: 5>, <Foo: 15>], [<Foo: 10>, <Foo: 15>]]

I've experimented with itertools but it doesn't seem particularly well-suited to my needs.

I think this could be accomplished with a complex QuerySet but I'm not sure how to start.