Function Decorators & Syntactic Sugar (@decorator)

1Concept

A decorator is a callable that takes a function as an argument and returns an augmented wrapper function. The `@decorator` syntax is syntactic sugar for `func = decorator(func)`.

2Architecture Diagram

@timer
def fetch_data(): ...
       |
       v Equivalent to:
fetch_data = timer(fetch_data)

3Code Example

import time

def timing_decorator(func):
    def wrapper(*args, **kwargs):
        start = time.perf_counter()
        result = func(*args, **kwargs)
        duration = time.perf_counter() - start
        print(f"[{func.__name__}] Executed in {duration:.6f}s")
        return result
    return wrapper

@timing_decorator
def compute_heavy_task(n: int) -> int:
    return sum(i * i for i in range(n))

res = compute_heavy_task(100_000)
print(f"Result: {res}")

4Expected Output

[compute_heavy_task] Executed in 0.005821s
Result: 333328333350000

5Key Takeaways

• ✓Decorators execute at function DEFINITION time (import time), not call time.
• ✓Always return the inner wrapper from the outer decorator function.
• ✓Decorators allow cross-cutting concerns (logging, auth, caching) without modifying core logic.