While I do see the desire to get your list back for such cases (I would have liked so, too, in some cases), it's inconsistent, as everything else operating in-place returns None.

Plus, having it return None helps you remember that you should keep the reference to your list around. What's more, making it return a value will often make newbies believe that they're two separate lists, and then wonder why the first one was shuffled too.

This is error-prone, and these arguments are why it returns None. It has been discussed in the past -- See http://stackoverflow.com/questions/17649875/why-does-random-shuffle-return-none which is related to your issue, and http://stackoverflow.com/questions/240178/python-list-of-lists-changes-reflected-across-sublists-unexpectedly to see what I mean by confused newbies.