Master Python Decorators: Syntax, Examples & Best Practices

def timer(func):
    import time
    from functools import wraps

    @wraps(func)
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        elapsed = time.perf_counter() - start
        print(f"{func.__name__} took {elapsed:.4f}s")
        return result
    return wrapper

@timer
def slow_add(a, b):
    time.sleep(0.1)
    return a + b

slow_add(3, 5)  # prints timing, returns 8

def retry(max_attempts=3, delay=1.0):
    import time
    from functools import wraps

    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            for attempt in range(1, max_attempts + 1):
                try:
                    return func(*args, **kwargs)
                except Exception as e:
                    if attempt == max_attempts:
                        raise
                    time.sleep(delay)
        return wrapper
    return decorator

@retry(max_attempts=5, delay=0.5)
def flaky_api_call():
    ...

class CountCalls:
    def __init__(self, func):
        self.func = func
        self.count = 0
        from functools import wraps
        wraps(func)(self)

    def __call__(self, *args, **kwargs):
        self.count += 1
        print(f"Call {self.count} to {self.func.__name__}")
        return self.func(*args, **kwargs)

@CountCalls
def greet(name):
    return f"Hello, {name}"

greet("Ada")  # Call 1
greet("Alan") # Call 2

@timer
@retry(max_attempts=3)
@CountCalls
def fetch_data():
    ...
# Execution order: CountCalls -> retry -> timer