Support Python 3.x

[njwilson]

I’d like to support Python 3.x sooner rather than later, but I’m not planning to invest much time in it until I have something working well enough on Python 2 for people to use. I’d be perfectly happy if someone else put some time into it though.

I don’t have much (any) experience with Python 3, but I think the best approach will be to maintain only one version of the code for Python 2 and run 2to3 on installation. See the 2to3 section of the Python 3 porting book for details. I'm happy to make the code look more like Python 3 (e.g., add parenthesis to the print statement), but prefer to avoid weird hacks like compatibility libraries. But as I said, I'm no expert on this.

Since I don't plan to support Python 2.5 (which is missing significant features that later versions have), supporting Python 3 really shouldn't be a big deal for this library. That is, assuming we don't have dependencies on packages that don't support Python 3 yet (I'd like to avoid depending on those packages). Having good test coverage will help make the whole thing easier as well.