I cheated and peeked at a solution for "Practice Makes Perfect."
I actually had a lot of the code correct, however I'm puzzled by this:
Define a second function called by_three that takes an argument called number.
if that number is divisible by 3, by_three should call cube(number) and return its result. Otherwise, by_three should return False.
OK, so I get all of it but the part where we say "== 0" Why is it equal to zero? Apologies if that's quite obvious to some of you. I don't quite have the hang of things.
if number % 3 == 0:
Replace this line with your code.