As a Python developer, usually this isn't a major problem for me when going out and finding libraries. Almost every library you find will support 2.7, so I pretty much stick to 2.7 when using or writing any code. I miss some of Python 3's good features but the library ecosystem is more important to me.

It's a real pain in the ass when I try to publish my own, though. The generally accepted rule is that all libraries must support 2.6 through 3.4, and this can be a major hassle.

But you can use Python 3, it is your business if you decide you don't want to.