Snakes Are Sinister Applied to Species
Cobras are the kind of snakes most often associated with villainy, due to their menacing-looking hoods and venom. Vipers (especially rattlesnakes) are not far behind cobras. By contrast, the most likely snakes to be exceptions of this are garter snakes, corn snakes, kingsnakes, and constrictors (boas and pythons), since these lack venom and even look cute as far as snakes go. In general, venomous snakes are universally perceived in fiction as the Unpleasant Animal Counterpart to non-venomous snakes, and this is especially practiced with cobras and pythons.
Pythons and boas tend to be portrayed as noble animals and being hungry predators at worst, similar to lions and eagles. In fact, in some African cultures pythons are considered the Token Heroic Orcs among snakes!
