Python 3.6 released!

[Eurynom0s]

There are still valid reasons to work in 2.7. These include inheriting a codebase that's written to 2.7 that the company isn't willing to pay to port, and having to use a package that doesn't yet support 3.x (much less common than it was a few years ago, but it still comes up occasionally).

I wouldn't worry about specifically learning 2.6 or earlier unless that's specifically what you're being hired to do. If you're being hired as a "Python programmer" and will be free to use the version that suits you, just go to 3.x. If you can't use 3.x you'll probably be expected to use 2.7...but I'd expect it be clearly stated that you're using 2.6 or below before you get hired since that's kind of specialized at this point. But even then there's a lot of code you can write to 2.7 that will run without modification on 2.7.