Yes, it is a rat snake. All black snakes are in fact black rat snakes. As hatchlings and even young adults they have the patterns that are common among rat snake but lose the patterns as they become adults. They are actually the same species of snakes as corn snakes which are actually red rat snakes but the corns keep their patters throughout their entire life. I used to have about thirty different types of rat snakes but of course the wife frowns upon that when you move in together.