Unfortunately, once you get python and SDL onto the DS there's not a whole lot of space left. It's only got 4 MB of memory to start with. I know, I know, I used to write games in 16K total, but script languages like python work on the idea that you trade some memory and speed for much faster development and superior maintainability. Most pygame games don't worry much about memory because of the obscene amounts available on even low-end PCs today - duplicating the screen surface? No problem at all! 80k sound samples? That's nothing! Of course that'll all bite you in the butt on the DS.
Still, it's sort of fun to write for severely space constrained devices, so if we did have pygame on the DS, I can't imagine you could just run most existing games on it, but it might be fun to see what you could do with games written specifically for it. Ron
