Python Decorators: A Complete Practical Guide

Decorators are a powerful Python feature that lets you modify function behavior without changing the function itself. Here's everything you need to know.

Complete Code Example

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():
    time.sleep(0.1)
    return "done"

slow_function()  # slow_function took 0.1001s

# 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("Python")  # Prints 3 times

# Class-based decorator
class Cache:
    def __init__(self, func):
        self.func = func
        self.cache = {}
        functools.update_wrapper(self, func)

    def __call__(self, *args):
        if args not in self.cache:
            self.cache[args] = self.func(*args)
        return self.cache[args]

@Cache
def fibonacci(n):
    if n < 2: return n
    return fibonacci(n-1) + fibonacci(n-2)

print(fibonacci(30))  # 832040 (fast due to caching)

💡 Pro Tips

• Always use @functools.wraps to preserve the original function's metadata
• Decorators are just syntactic sugar for function composition
• Use class-based decorators when you need to maintain state

Why This Matters

Understanding these Python features will help you write more:

• ✅ Readable and maintainable code
• ✅ Memory-efficient applications
• ✅ Pythonic, idiomatic solutions

Summary

Mastering Python's built-in features is key to becoming a better developer. Practice these examples in your own projects, and you'll quickly see the benefits.

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