Pydoc, pytest and mypy are simple, powerful, underused tools.<p>@dataclass can make a lot of code cleaner than it would be otherwise.<p>Sum types, only available as of 3.10, make a lot of things easily expressible now that were extremely awkward previously.<p>Also, learn Haskell. It forces you to learn to keep most of your code pure, limiting IO to a thin top level layer, which makes testing and hence correctness a lot easier.