How to convice my parent to havingg ball pythons inside the house?

[Bogertophis]

The best you can do is educate them.

I wrote an entire ESSAY trying to convince my parents to get a snake and answered all their questions and they realized how harmless they were along with the fact they wouldn't have to interact with it and said yes. (The only downside is I have to pay for it all... I guess that's fair though, kinda hard to make money when you're 13 but I am DETERMINED.)

So even if you educate them about all their concerns, yet they say no you gotta respect that.

Putting it all down on paper really shows how much thought & preparation you've put into this. And I think they respected that...
Another way is to list all their objections & answer each one...writing practice comes in handy your whole life, believe me, and it shows you can think logically.
If they still have questions, you could also send them here to ask us themselves, or possibly check out sources from the library.