Kotlin Cheatsheet: let / apply / also / run / with
Five scope functions cover ~95% of "do something with x" patterns. Pick by two axes: receiver (this vs it) and return value (object itself vs block result).
Forget os.path.* — pathlib.Path is the modern, OS-aware way to work with paths. Operator overloading for joins, attribute access for components, methods for reads/writes/iterations.