How difficult is it to learn Python 2 if you know Python 3?

At your level, it's basically the same language with a few minor differences. It will be very easy to adapt.

It wont make much of a difference at your level. But you may get addicted to Python 2 beware ;)

There are no real differences - the structure of the language remains the same; you won't really need to learn anything, maybe just change a few small habits. You should read the list of change: https://docs.python.org/3.0/whatsnew/3.0.html The main advantage of Python 2 is the extensive amount of support and packages it has that have not yet been ported to Python 3. I will gladly switch to Python 3 (I already use it for some things) when the huge Python 2 package community moves to Python 3. You saw an example of this yourself - Django still uses Python 2 (when the question was asked - now it supports Python 3).