2.12 Decorators and closures
You can add timing, caching or retries without touching a function's body.
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Decorators wrap behaviour — timing, caching, retries — around a function without editing its body, and frameworks ahead use them constantly for routes, fixtures and tool registration. Writing one from scratch demystifies the at-sign permanently. It sits here because it composes closures from earlier. The small omission with large consequences is functools.wraps; leave it out and the wrapped function loses its name and docstring, confusing every tool that introspects it.
Work through these
Functions as first-class objects
Functions in Python are values that can be passed around and returned like anything else. This one fact is what makes everything else in this topic possible.
Writing a decorator with functools.wraps
Wrapping a function to add behaviour before or after it, while preserving its name and description. The preservation step is small and frequently omitted.
Decorators with arguments
A decorator that itself takes settings requires an extra layer of nesting, which is the part that reads confusingly the first few times. Working through one example makes it click.
lru_cache, retry and timing decorators
Caching results, retrying on failure, and measuring how long something took, all added without editing the function being wrapped. These three cover most practical decorator use.
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