It's pretty obvious, when you think about it - but if you can't work it out, then use the debugger to follow through what exactly your code is doing. If you don;t know how to use it, then it would be a really good idea to learn - it's a lot easier to do that on a tiny bit of code like this than it would be on a 100,000 later project!
This will help you learn how:
python debugger - Google Search[
^]
Hint: keep an eye on what happens to the head of the list.