Might seem picky but make sure you're keeping track of what does what.
Return has a special meaning, print doesn't return anything, it's not even a function (although in python 3 it is)
print is also not appending anything, right.
Read your function and keep track of what's being done to what you return. (nothing at all is done, why is that? read that code, what do you return and what do you do to that?)
Don't stare at it, because it's not going to pop out at you. You gotta follow it. Keep in mind that everything is carried out exactly the way it says, nothing will get corrected no matter how obvious that something else was meant.