I think the recommendation to study Flask's code base is an echo from years ago, when it was considered a micro/toy framework. I used to recommend it too. As a

I think the recommendation to study Flask's code base is an echo from years ago, when it was considered a micro/toy framework. I used to recommend it too. As a more seasoned programmer, I don't anymore. Having used and studied the framework, I've seen some of the limitations that directly stem from some of its design choices. Today, I think it tried to be needlessly clever sometimes. Some of those choices, that seemed fun and clever back in the days, did not age well. As time went and people started pushing the framework, some artefacts required hackish workarounds. And those kept cumulating. To such an extent that the codebase now has a bunch of flags that control it's contingent behavior; ifs and buts that make the whole thing harder to reason about. You'll still learn lots of clever Python tricks, but I wouldn't put it in the "clean and clear" category.