Pydoc, pytest and mypy are simple, powerful, underused tools.
@dataclass can make a lot of code cleaner than it would be otherwise.
Sum types, only available as of 3.10, make a lot of things easily expressible now that were extremely awkward previously.
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.
