burm bedding

is aspen a good substrate to be used with a burmese python?

IMO yes. Many people will suggest news paper since aspen will be expensive to replace a full grown burm cage worth but its absorbant which is helpful. Many Many layers of news print will also make clean up a breezer and cheap. A large python will Poo and urinate a good amount so something absorbant is a MUST!!

poop is gross

I use cypress or hardwood mulch with my Burmese. It is fairly absorbant and easy to spot clean. It holds humidity very well, looks good in my opinion, and it provides for easy sloughing.