Decorators in Python

Decorators let you add reusable logic to functions without changing the core code. They are wrappers that enhance the functions — perfect for logging, authentication, caching, or timing execution.

But what is a Decorator?

A decorator is simply a function that takes another function as an argument, adds some behavior, and returns a new function.

A small example -

def first_decorator(func):
    def wrapper():
        print("Function starting")
        func()
        print("Function ended")
    return wrapper
@first_decorator
def helloworld():
    print("Hello, World!")
helloworld()

And the output -

Function starting
Hello, World!
Function ended

A Practical Example

import time
import logging
logging.basicConfig(level=logging.INFO)
def log_api_call(func):
    def wrapper(*args, **kwargs):
        start = time.time()
        logging.info(f"Calling: {func.__name__}")
        result = func(*args, **kwargs)
        end = time.time()
        logging.info(f"Completed {func.__name__} in {end - start:.2f}s")
        return result
    return wrapper
@log_api_call
def fetch_user_data(user_id):
    time.sleep(1)  # Simulate API call
    return {"id": user_id, "name": "John Doe"}
@log_api_call
def fetch_orders():
    time.sleep(2)  # Simulate another API call
    return [{"order_id": 1, "amount": 100}]
fetch_user_data(42)
fetch_orders()

And the output -

INFO:root:Calling: fetch_user_data
INFO:root:Completed fetch_user_data in 1.00s
INFO:root:Calling: fetch_orders
INFO:root:Completed fetch_orders in 2.00s

Now, every API function logs automatically — no code duplication.