Pretty much the stuff already mentioned elsewhere on HN for this article. I often find Werkzeug's excellent debugger is enough: https://news.ycombinator.com/item?id=19718869 . pdb/ipdb/pudb et al (pick your fav) can help for really tricky stuff. And sufficient logging, so you know what's going on at all times even without a debugger attached.

(occasionally, the low effort of print-debugging works, but if you keep having to print in more/different locations... it's a blunt tool IMO)

I try to have "debug calls" that I can call from the browser or Postman or Swagger, etc. and return all sorts of debug information, etc.

I have the impression that local program-specific debugging tools quickly evolve into something like functional tests that uncover issues that functional tests proper might not cover. For example, if I'm serving a ML model but I have a debug call that runs sanity checks on the data that are too expensive to run each time.