Python 装饰器

装饰器是 Python 的语法糖，用于在不修改原函数代码的情况下扩展函数行为。

基本装饰器

def timer(func):
    import time
    def wrapper(*args, **kwargs):
        start = time.time()
        result = func(*args, **kwargs)
        print(f"{func.__name__} 耗时: {time.time() - start:.4f}s")
        return result
    return wrapper

@timer
def slow_function():
    import time
    time.sleep(1)

slow_function()  # slow_function 耗时: 1.0012s

@timer 等价于 slow_function = timer(slow_function)。

functools.wraps

保留原函数的元信息：

from functools import wraps

def timer(func):
    @wraps(func)  # 保留 __name__, __doc__ 等
    def wrapper(*args, **kwargs):
        # ...
        return func(*args, **kwargs)
    return wrapper

带参数的装饰器

def repeat(n):
    def decorator(func):
        @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("Tom")  # 打印 3 次

类装饰器

class CountCalls:
    def __init__(self, func):
        self.func = func
        self.count = 0

    def __call__(self, *args, **kwargs):
        self.count += 1
        print(f"调用次数: {self.count}")
        return self.func(*args, **kwargs)

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

常用内置装饰器

class MyClass:
    @staticmethod
    def static_method():
        pass

    @classmethod
    def class_method(cls):
        pass

    @property
    def name(self):
        return self._name

    @name.setter
    def name(self, value):
        self._name = value

装饰器叠加

从下往上包装，从上往下执行：

@decorator_a
@decorator_b
def func():
    pass

# 等价于
func = decorator_a(decorator_b(func))

实用示例

from functools import wraps
import time

# 缓存
def memoize(func):
    cache = {}
    @wraps(func)
    def wrapper(*args):
        if args not in cache:
            cache[args] = func(*args)
        return cache[args]
    return wrapper

# 重试
def retry(max_attempts=3, delay=1):
    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            for attempt in range(max_attempts):
                try:
                    return func(*args, **kwargs)
                except Exception as e:
                    if attempt == max_attempts - 1:
                        raise
                    time.sleep(delay)
        return wrapper
    return decorator