pass on the corn snakes. go for a ball python. they get about 3.5ft, very good temperment and the morphs are just amazing.
I have two ball pythons one in a 55gallon tank and one in a plastic storage bin. The cat sits on top of the plastic bin since he has no idea whats inside nor does he care.
The only time you might ever run into a problem is when you take your snake out and your cats around. snakes have poor eye sight like somone earlier said. if your cat is coming close moving fast the snake might react to that. not in a positive way. We make it as hard as possible for our cats to get close to your 55gallon tank since in ball pythons they can be stressed easily, the last thing we want is the cat taunting him.
If your really interested in getting a snake go for a ball
I would love to tell you all about them hehehahaha!
Also really look into the types of enclouser you want and what saftey percautions you might need to make.
Snakes are amazing creatures and are a great pet and hobby to get into!