20 gals for a baby ball python would be big though.. try starting from 10gals.. they are relatively cheap or buy a 18qt sterilite which is cheaper and holds humidity very well. keep the 20gals till it gets bigger.

bigger tanks will tend to increase the stress the snake would be experiencing. have fun with your new hobby.

I'll give you some words of caution though, this hobby is addicting! you start with 1 snake and weeks later, you want more!