Closures, laziness, context managers, and writing composable higher-order utilities.
3 questions in Python.
A try/finally around the yield. @contextmanager throws the body's exception into the generator at the yield, so a release written after the yield is skipped. Wrap the yield in try/finally, or use with lock inside it, and re-raise anything you catch, or the generator suppresses the caller's error.
Decoration runs once, at definition time, so it happens on import rather than on call. Stacked decorators apply bottom-up and execute outermost-first, and each wrapper replaces the function's identity unless functools.wraps restores it, which is what breaks introspection and framework registration.
A generator produces items on demand and keeps only the current item plus its suspended frame, so memory stays flat as the input grows; it is the wrong tool when you need a length, indexing, or more than one pass, and when per-item resume overhead outweighs the space saved.