This is also a program that you could have coded.

This sample program was written with the goal of being polished. This is a great example where the implementation is not trivial (unlike in Tic-Tac-Toe), so abstraction is vital to prevent bugs and to keep the code readable.

There are some Python things in the code that you may not know yet. The assert statement just throws an error if the following condition isn't true. Writing a string with the % symbol lets you plug in the variables that follow into that spot in the string (%s means string, %i means integer and %c means one letter).