His soul was split into 7, depriving him of happiness or love. Those things are vital to conjuring a Patronus, so he has none. There is even evidence, I read it somewhere, but unfortunately, I don't remember the website.

Lmao, true! Never thought about it! ;D

A Serpent after all he was evil, sly and the heir of salazar slytherin(my theory)

He didn't as he was on the side of what patronuses where trying to destroy. This made him incapable of casting a patronus.

Snake

He wouldn't bw able to create any..he don't have happy memories

Snape was the only death eater able to cast a corpreal patronus (doe)

Snake

Nigini