Full Grown Ball Python in 20 gallon?

[55fingers]

Personally I would only put a very small male in a 20 gallon long. If it's not a long then I wouldn't keep one in it. Tell him the temperature and humidity requirements for a ball python. If the temps and humidity are not met, then ball pythons can go off feed for weeks, months, and there's even been cases of years! This can put a lot of stress on you and the snake, and you might end up with a lot of vet bills to pay if he starts loosing a lot of weight and you have to check on him at the vet during his fasting.

Tanks can be used only if you are willing to put in the work and time to maintain the humidity and temps. Depending on how much humidity you generally get where you live, you will more than likely have to cover the screen of the tank with layers of foil, plexiglass (which can be pricey), or a towel you have to dampen every time it dries out, you will have to mist multiple times a day, get a substrate that holds humidity (which you will also have to dampen every time it dries out), you may not be able to use an overhead heat source, and you might want to get a fogger/mister on a timer, a bigger water bowl, etc. Then for the temperature, you may need to add insulation to the outside and or multiple heat sources (which means multiple thermostats and can get very expensive). A lot of time and work compared to a tub which tends to keep the temperature and humidity in without many adjustments. Even after all of this, be aware that ball pythons are not very good display animals and you probably won't see it much since they hide all day, which kind of defeats the purpose of working so hard with a tank.

I used to use a tank, it's definitely possible to keep a snake in one, but a lot of work. I recently switched to a tub and won't ever go back. I hardly need to do any maintenance apart from changing the water and spot cleaning. Not to mention a tub is so much cheaper than a tank, doesn't take up as much space, and is much lighter.

Maybe think about investing in or saving up for a custom enclosure like from animal plastics. They have the visibility of a tank while keeping the temp and humidity within range. Most would agree they are the best enclosure for a snake.

So yes, you can use a tank. I don't bash on those who do, as long as they can, again, put in the extra time and work to provide adequate husbandry and care. If you want to use a tank, go ahead, but what concerns me is your fathers attitude towards this all? If he hasn't done the research, he probably doesn't know what's best for the snake. Make sure if you're dedicating the next 30+ years to this snake that you won't compromise its husbandry and care just because someone else says so. If your father is going to stop you from taking care of the snake properly because he decides that's not how you take care of one (despite numerous of experienced breeders and keepers saying otherwise) then perhaps wait until you can pay for the snake yourself. What happens if he decides the snake should eat prey smaller than it's supposed to? Or says he heard the snake doesn't need hides? Or thinks it's ridiculous to spend money on a thermostat?

I'm not trying to be hostile or say you outright shouldn't get a ball python.. but just make sure to do your research and be careful.