It's hard to write libraries in both versions. At the moment, Python 2 may be more productive, because it's got more libraries. But the way things are going,

It's hard to write libraries in both versions. At the moment, Python 2 may be more productive, because it's got more libraries. But the way things are going, Python 3 will soon reach parity, and eventually take over. If that happens, it was no longer a smart choice to go Python 2 for a new project. I'm not saying you should port old code anytime in the next few years (unless it's a library). But it's probably worth thinking about whether or not new projects should use Python 3.