I learnt Python with its 3.0 and 3.1 releases. They did some significant changes (including the syntax) from 2.x to 3.x but the 2.x version remains popular. (And I think that's why officially Python is still maintaining and offering both 2.x (latest 2.7) and 3.x (latest 3.2) at the same time).

I guess it won't hurt to provide both on codeforces, like KK123 said, there are also some other programming practice sites doing that.

I was looking at your post and then I accidentally clicked the "Do Not Like It" button. I am so sorry about that. I really didn't mean to click it.

(At first I thought that down-arrow button would expand the screen and show more details, like the list of comments etc.)