If you parents do not want snakes in THEIR home you have to respect that and please do not buy an animal without their consent it puts everyone in a bad position starting with you, the seller and most importantly the animal.
If an animal was brought into my house without my consent that animal would return where it came from with some people it could be far worse.
I lived in a "no snake" household (everything was allowed but snakes) and I did just fine, I grew up, traveled a bit, lived in different countries than when I finally settled down and bough my first home I bought one snake than two than well let's say that one snake room turned into two. Now looking back it was a good thing because a snake is a LONG commitment and I would have been unable to live the life I lived if I had a snake and kept it.
Bottom line THEIR house, THEIR rule so if they say no it's ook because if you are passionate now you will be passionate in 5, 10 or even 20 years from now.