I'm going to put aside my own personal beliefs of purpose for a second.
You have a point: The purpose was served. However, the purpose wasn't just to feed the python. It was done for entertainment, that is clear as crystal. It was a sadistic action. And objectively speaking, a person who abuses animals is more likely to commit violent crimes against other humans than most others. This is recognized universally, even though it tends to be glanced over. This action shows a complete lack of empathy towards another living being that is widely seen as a friendly pet. It isn't as if the guy started slapping a house fern, he was the reason an animal died and was both willing and happy to be that reason. There is absolutely nothing else behind this besides him wanting to see the cat be eaten.
Was entertainment a purpose or was it a convenient addition.
If my arm got cut off I might eat it just to see what it would be like. Eating it was not why I cut it off, it was just something that I would only get one chance to do and had an opportunity.
