Decorators (Function & Class)

import functools
import time

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

@timer
def slow_function():
    total = sum(range(1_000_000))
    return total

result = slow_function()

# Decorator with arguments
def repeat(n):
    def decorator(func):
        @functools.wraps(func)
        def wrapper(*args, **kwargs):
            for _ in range(n):
                result = func(*args, **kwargs)
            return result
        return wrapper
    return decorator

@repeat(3)
def greet(name):
    print(f"  Hello, {name}!")

greet("Alice")

# Practical: logging decorator
def log(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print(f"  Calling {func.__name__}({args}, {kwargs})")
        result = func(*args, **kwargs)
        print(f"  {func.__name__} returned {result}")
        return result
    return wrapper

@log
def add(a, b):
    return a + b

add(5, 3)

# Built-in decorators
# @property, @classmethod, @staticmethod
# @functools.lru_cache — memoization
@functools.lru_cache(maxsize=128)
def fibonacci(n):
    if n < 2: return n
    return fibonacci(n-1) + fibonacci(n-2)

print(f"\nfib(30) = {fibonacci(30)}")