Good programming practices are crucial for producing reliable and re-usable code, but are rarely taught in astronomy-based programming courses. Inquiry-based lessons are well-suited to teaching these practices, as they can give students the chance to try writing code---which may or may not conform to programming standards---and then explore what makes their code more efficient and comprehensible. We present one example of such a lesson, developed as part of the Institute for Scientist and Engineer Educators Professional Development Program (ISEE PDP).