With programmers, the single easiest way to identify good candidates (in my experience) is sheer interest in what they do / desire to learn. This is a learn everyday field and if you're interested in what you're doing, you're going to do a lot better at it. It's hard to apply yourself mentally to something that you don't have a good level of interest in. Given that it's a learn everyday field, people with that level…
They may be able to hack around, write a for loop, track down a bug....but you're not going to get the same caliber of work from someone who first saw python two weeks ago compared to someone whose been using the language for 5 years on real projects.