What are Python decorators and how do they work?

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A decorator is a function that wraps another function to extend or modify its behavior — without changing its source code. It's syntactic sugar for the higher-order function pattern. How they Works Under the hood, when you write @my_decorator above a function, Python is essentially doing func = my_decorator(func) — it passes the original function into the decorator and replaces it with whatever the decorator returns, which is typically a wrapper function. Mental model — the sugar: @timer def work(): ... # is exactly equivalent to: def work(): ... work = timer(work) Basic decorator: import functools, time def timer(fn): @functools.wraps(fn) # preserves name, docstring, signature def wrapper(*args, **kwargs): t0 = time.perf_counter() result = fn(*args, **kwargs) print(f"{fn.__name__} took {time.perf_counter() - t0:.4f}s") return result return wrapper @timer def heavy(n): return sum(range(n)) Decorators with arguments — add one more layer of nesting (a decorator factory ): def retry(times=3): def deco(fn): @functools.wraps(fn) def wrapper(*args, **kwargs): for i in range(times): try: return fn(*args, **kwargs) except Exception: if i == times - 1: raise return wrapper return deco @retry(times=5) def flaky(): ... Show a practical decorator (timer or retry), explain how it works (@syntax is sugar for function reassignment), and always use functools.wraps. The decorator-with-arguments pattern (triple nesting) is the advanced follow-up. Mention @lru_cache, @property, @staticmethod as built-in examples.