22. Decorators

A decorator is a function that takes a function and returns a (usually wrapped) function, applied with `@decorator` syntax.

python
import functools

def log_call(fn):
    @functools.wraps(fn)
    def wrapper(*args, **kwargs):
        print(f"calling {fn.__name__}")
        return fn(*args, **kwargs)
    return wrapper

@log_call
def mint(amount):
    return amount

mint(5)   # prints "calling mint", returns 5

`functools.wraps` preserves the original function's name and docstring, which matters for debugging and introspection. Decorators are commonly used for logging, timing, caching (`functools.lru_cache`), and access control.

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