If you’re writing code. Ever. Be it Java, Python, Objective-C, Perl, or plain old C, you really, really need to get in the habit of using a version control system for managing your code. It allows you to experiment, and to easily roll back your code if you completely mess something up.
There are several excellent and simple systems available. My preferred system is Git, but Mercurial is also an excellent, modern system to use. It’s also fairly easy to set up. And if you don’t want to mess around with the command line a lot, or don’t want to pay for the (excellent) Tower, then there’s a new, free option for managing your git repositories at the popular online service GitHub. (Note – you don’t need to host your repositories online – they never have to leave your computer. Unless you want to share them with other people not in your home or office).