Comment by 3pt14159

The right advice to give new hires, especially junior ones, is to explain to them that in order to have a good first PR they should read this Wikipedia page first:

https://en.wikipedia.org/wiki/Code_smell

Also helpful are code guidelines like the one that Google made for Python:

https://google.github.io/styleguide/pyguide.html

Then when their first PR opens up, you can just point to the places where they didn't quite get it right and everyone learns faster. Mentorship helps too, but much of software is self-learning and an hour a week with a mentor doesn't change that.