Nice snake but I don't think ground up walnut shell with its food would be any good for it. I did a bit of part time work in a place which polished quantities of small pieces of brass and copper. They used ground walnut shell in a cement mixer because of its hardness and jagged edges to polish the metal.
I have seen aquarium gravel, bark chip, aspen bedding or similar brand, breeders choice or similar brand recycled paper pellets and paper just to name a few. I think the reptile expert at the petshop was more expert at taking your money.
I have over twenty pythons and I find the easiest is to use paper towel for the hatchlings (in click clack containers) and butchers or newspaper for the older snakes (in enclosures). Very easy to just roll up when soiled, throw it, then spot clean with weak F10 solution and a paper towel wipe out between full cage cleans.
Hope this helps.
Octane