Python Decorators & Generators

# Decorator basics
def timer(func):
    import time
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        end = time.time()
        print(f"{func.__name__} took {end-start:.4f}s")
        return result
    return wrapper
@timer
def slow_add(a, b):
    import time
    time.sleep(0.1)
    return a + b
result = slow_add(10, 20)
print(f"Result: {result}")
# Practical decorator — login required
def login_required(func):
    def wrapper(user, *args, **kwargs):
        if not user.get("logged_in"):
            print("Access denied! Please login. ❌")
            return
        return func(user, *args, **kwargs)
    return wrapper
@login_required
def dashboard(user):
    print(f"Welcome to dashboard, {user['name']}! ✅")
dashboard({"name": "Rahul", "logged_in": True})
dashboard({"name": "Guest", "logged_in": False})
# Generator basics
def countdown(n):
    while n > 0:
        yield n
        n -= 1
for num in countdown(5):
    print(num, end=" ")
print()
# Generator for large data (memory efficient)
def fibonacci(limit):
    a, b = 0, 1
    while a < limit:
        yield a
        a, b = b, a + b
fib = list(fibonacci(100))
print(f"Fibonacci: {fib}")
# Generator expression (like list comp but lazy)
squares_gen = (x**2 for x in range(1, 1000001))
print(f"First 5 squares: {[next(squares_gen) for _ in range(5)]}")