What size of an enclosure are you planning to use? Even for a Children Python (about 2-3 feet) needs something tall for climbing, like a 29 gallon tall at minimum. A gray banded king is slightly smaller than a CP but I would not house it in less than a 20 gallon long. In other words, finding a snake that can stretch out or live comfortable and with spare space to move around in a 10 gallon tank or smaller is quite the challenge. While it can be done with CP or GBK or others to keep them in a 10 gallon tank, the question is should you? Adding 2 hides and a water bowl immediately takes up most of the floor space. You will probably need to look into the less commonly kept snakes, mostly likely imports, and they usually come with feeding challenges as mentioned by the other posts.
The only kind of pet that I can think of that could be kept comfortably in a 5-10 gallon tank is a small group of 3-4 neon tetras fish.