I'm a landlord and a tenant, and I'm usually very much 'ask permission for everything', however for a snake, I probably wouldn't ask. I've never kept a snake but as far as I'm aware there is NO way it could damage the property, right? It's only pets that could cause damage to the property in any way that I would be opposed to tenants not seeking permission for.
I actually have pets that I didn't ask permission for. However they are kept in a cage/tank, one never ever comes out and the other three the kids hold but they are not allowed down on carpet or anything else that can get damaged. So I see no reason to ask. Also, as Lilypily demonstrated , any pets that are unusual, people may decline just for the reason of their irrational fears, not because they think they are not suited to the property. So I also didn't seek permission for my pets for that reason.