When prettyprinting lists, add a final ","

It doesn't hurt, and means you can safely reshuffle the order of the
lines if order is not relevant, or add another line anywhere in the
list/tuple/dict/set/whatevs.

Also makes for smaller context/unified diffs if you do change things
around.
It's okay to return early

Not really needed in this case but can flatten nested ifs/elifs and exit
before a potentially heavy test is performed