I'd say it's either a northern pine or an anery corn snake; both are harmless. We had an anery corn snake named Candycorn - lived to 7 and grew to 5.2 ft.
If you go outside and alarm the snake (wave a stick in its general vicinity). If it starts shaking it's tail like a rattler and violently hisses at you - that's a northern pine trait. If it does pretty much nothing...or slinks away, or acts curious in regard to the stick - it's probably an anery corn.
I don't know anything about snakes other than my own experiences with Candy. I'm sure others on the board will chime in to help you.
I'm quite sure it's a corn snake. Named that because they live in the corn fields down south and eat mice and rats. They are a very common pet snake.
Where are you located?
I'm pretty sure that's what it is... very harmless unless you're a mouse.