If you mean an A-rated Python with money left over for mining gear on top of at least a few rebuys, then it might be worth considering if you're really not happy with your current ships. The Python is arguably the best example of a true "do anything" ship, so it wouldn't pigeonhole you into into a single playstyle.
But saying that, it's nice to keep a stable of ships rather than going all in with a single one. If you don't want to wait until you can get a Python without selling anything, I'd suggest at least saving enough to buy one by selling modules rather than whole ships. You don't lose any money by selling modules, but hulls do depreciate.
Do what makes you happy. Just whatever you do, don't end up flying a budget Python without rebuy.