Two Scoops of Django is one of my favorite books! As to how popularity score is calculated: I used the Amazon Bestseller Rank of the book to assign a score for popularity. This rank loosely indicates how many copies of the book were bought recently. I found this to be well correlated with quality (I know many of these books by experience, and I found that the ones that I already knew to be good books rose to the top). In addition, when you filter for topics in the beginner section, another score is assigned based on relevance to those topics. This was a bit more work. I went through the contents of the book manually and tagged each book by the topics it covers and the percentage of the book devoted to that topic. After the relevance score is computed, it is combined with the popularity score to get a final score.