Python

Seconding this. For someone that doesn't know anything about Python, there are vital aspects of Python 2 that need to be covered.

In the context of learning a language, most of the time, a lower version number doesn't mean that much. In the case of Python 2, there are fundamental incompatibilities - and, as you say, it's still out there, and when your see it, you need to know what that means.

Maybe you don't choose a library or a piece of software if you notice it. Maybe you get a legacy code base dumped on your lap. This shit happens.