Decorator Patterns

Decorator composition, parameterized decorators, and patterns.

Overview

Master decorator patterns.

Parameterized Decorators

import time
from functools import wraps

def rate_limit(calls_per_second=1):
    min_interval = 1.0 / calls_per_second
    last_called = [0.0]
    
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            elapsed = time.time() - last_called[0]
            left_to_wait = min_interval - elapsed
            
            if left_to_wait > 0:
                time.sleep(left_to_wait)
            
            ret = func(*args, **kwargs)
            last_called[0] = time.time()
            return ret
        return wrapper
    return decorator

@rate_limit(calls_per_second=2)
def api_call():
    print("API call made")

# Can make 2 calls per second

Decorator Composition

def bold(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return f"<b>{func(*args, **kwargs)}</b>"
    return wrapper

def italic(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        return f"<i>{func(*args, **kwargs)}</i>"
    return wrapper

@bold
@italic
def greet(name):
    return f"Hello, {name}"

print(greet("Alice"))  # <b><i>Hello, Alice</i></b>

Class-Based Decorators

class CountCalls:
    def __init__(self, func):
        self.func = func
        self.num_calls = 0
    
    def __call__(self, *args, **kwargs):
        self.num_calls += 1
        print(f"Call {self.num_calls} to {self.func.__name__}")
        return self.func(*args, **kwargs)

@CountCalls
def say_hello():
    print("Hello!")

say_hello()  # Call 1 to say_hello / Hello!
say_hello()  # Call 2 to say_hello / Hello!

Practice

Create a decorator that logs function calls to a file.