Just note--dogs were not selectively bred by humans in any deliberate fashion. Their ancestors simply scavenged the leavings from groups of humans, and the ones that were less aggressive were tolerated and allowed to come closer--so they got more food, and were more successful. Thus, the domestication of the dog was more of an evolution of the dog to take better advantage of us, not us making the dog into something we wanted. Dogs are superb 'nest parasites'--they have learned us so well that we treat them like our own children--we feed and care for them, and it's all because they look cute, pay attention to us, and occasionally help us out.

Cats are fully domesticated animals. So are ferrets, lab rats, lab mice, domestic rabbits, chickens, cows, horses, farm pigs, goats, sheep, etc. The primary traits that set domestic animals apart from wild animals are an inherent reduction in aggression toward humans, and the ability to pay attention to and respond to human body language cues. Domestic animals are more passive, less nervous, and 'friendlier'. The neotenous traits and coat color variations they show appear to be a natural result of breeding for reduced human aggression. Whether it occurred naturally or was done deliberately by humans, the result is the same.

See the fox fur farm experiments for details--a domesticated breed of foxes was created, and it took surprisingly little time (only 40 years!), and came with MANY unexpected side effects.
http://www.freerepublic.com/focus/news/807641/posts

This article also demonstrates why ball pythons aren't domesticated. That is not to say that we can't domesticate them! In fact, I encourage it. Don't just breed for looks--breed for temperament, and do it consistently. With selective breeding for temperament over the next 100 to 150 years, we should produce a significantly different animal--one that is far more trustworthy and consistent in its behavior, one that is better adapted to captive conditions--yes, one that is in fact domesticated. It will be better for reptile owners, and it will be better for the snakes themselves. There is no reason to 'keep them wild'--they will never go back to the wild, they and their offspring will always be captive. Changing them to be better pets can only benefit them.