Sometimes its not a state law, but just a county law. In texas, they're legal, but in the county I go to college...the pet laws are a mess. It technically says no "constrictors," but as I worked in a pet store, I know exactly what is and isn't allowed. Corns/milk/king/bull snakes, good, and anything else is outlawed. However, you can buy a permit for the giant snakes at walmart, but there is no way to obtain a permit for those in the middle, such as balls. Wierd as it may be, I know this from experience...before deciding to get a ball and break the law, I tried to get a permit and was told theyre just not allowed.
For some reason, there are just a small amount of snakes that are not legal, and there is no way to get a permit. Some places will be like that, and you just have to be careful if you decide to get one.