I had an interview a few days ago, and just punched the problem I was asked to do in Python into iPython. Immediately did it a much simpler way, and also spotted my logic error (if you want deciles you actually divide by 9, not 10, since you have 9 columns with 10 edges).

Took me about 2 minutes to do. Whereas in the interview I wrote entirely the wrong thing initially, then went "oh wait, that makes no sense".