Python装饰器（Decorators）深度解析

作为一名从后端开发转向Rust的开发者，我发现Python的装饰器与Rust的特质（Traits）有一些相似之处，它们都可以用于扩展代码的功能。今天我想分享一下我对Python装饰器的理解和实践。

什么是装饰器？

装饰器是一种特殊的函数，它可以修改其他函数或类的行为。装饰器的语法使用@符号，放在被装饰函数或类的定义之前。

@decorator
def function():
    pass

这相当于：

def function():
    pass

function = decorator(function)

装饰器的基本实现

1. 简单装饰器

def simple_decorator(func):
    def wrapper():
        print("Before function execution")
        func()
        print("After function execution")
    return wrapper

@simple_decorator
def hello():
    print("Hello, world!")

# 调用函数
hello()

输出：

Before function execution
Hello, world!
After function execution

2. 带参数的装饰器

def decorator_with_args(prefix):
    def decorator(func):
        def wrapper():
            print(f"{prefix}: Before function execution")
            func()
            print(f"{prefix}: After function execution")
        return wrapper
    return decorator

@decorator_with_args("LOG")
def hello():
    print("Hello, world!")

# 调用函数
hello()

输出：

LOG: Before function execution
Hello, world!
LOG: After function execution

3. 保留函数元数据的装饰器

import functools

def decorator_with_metadata(func):
    @functools.wraps(func)
    def wrapper():
        print("Before function execution")
        func()
        print("After function execution")
    return wrapper

@decorator_with_metadata
def hello():
    """Print hello message"""
    print("Hello, world!")

# 调用函数
hello()

# 查看函数元数据
print(f"Function name: {hello.__name__}")
print(f"Function docstring: {hello.__doc__}")

输出：

Before function execution
Hello, world!
After function execution
Function name: hello
Function docstring: Print hello message

4. 带参数的函数装饰器

import functools

def decorator_with_args_and_function_args(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print("Before function execution")
        result = func(*args, **kwargs)
        print("After function execution")
        return result
    return wrapper

@decorator_with_args_and_function_args
def add(a, b):
    """Add two numbers"""
    return a + b

# 调用函数
result = add(1, 2)
print(f"Result: {result}")

# 查看函数元数据
print(f"Function name: {add.__name__}")
print(f"Function docstring: {add.__doc__}")

输出：

Before function execution
After function execution
Result: 3
Function name: add
Function docstring: Add two numbers

装饰器的高级用法

1. 类装饰器

class ClassDecorator:
    def __init__(self, func):
        self.func = func
    
    def __call__(self, *args, **kwargs):
        print("Before function execution")
        result = self.func(*args, **kwargs)
        print("After function execution")
        return result

@ClassDecorator
def hello():
    print("Hello, world!")

# 调用函数
hello()

输出：

Before function execution
Hello, world!
After function execution

2. 带参数的类装饰器

class ClassDecoratorWithArgs:
    def __init__(self, prefix):
        self.prefix = prefix
    
    def __call__(self, func):
        def wrapper(*args, **kwargs):
            print(f"{self.prefix}: Before function execution")
            result = func(*args, **kwargs)
            print(f"{self.prefix}: After function execution")
            return result
        return wrapper

@ClassDecoratorWithArgs("LOG")
def hello():
    print("Hello, world!")

# 调用函数
hello()

输出：

LOG: Before function execution
Hello, world!
LOG: After function execution

3. 装饰器链

import functools

def decorator1(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print("Decorator 1: Before function execution")
        result = func(*args, **kwargs)
        print("Decorator 1: After function execution")
        return result
    return wrapper

def decorator2(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print("Decorator 2: Before function execution")
        result = func(*args, **kwargs)
        print("Decorator 2: After function execution")
        return result
    return wrapper

@decorator1
@decorator2
def hello():
    print("Hello, world!")

# 调用函数
hello()

输出：

Decorator 1: Before function execution
Decorator 2: Before function execution
Hello, world!
Decorator 2: After function execution
Decorator 1: After function execution

4. 装饰器用于类方法

import functools

def method_decorator(func):
    @functools.wraps(func)
    def wrapper(self, *args, **kwargs):
        print("Before method execution")
        result = func(self, *args, **kwargs)
        print("After method execution")
        return result
    return wrapper

class MyClass:
    @method_decorator
    def hello(self):
        print("Hello, world!")

# 创建实例并调用方法
obj = MyClass()
obj.hello()

输出：

Before method execution
Hello, world!
After method execution

装饰器的应用场景

1. 日志记录

import functools
import time

def log_execution(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        start_time = time.time()
        print(f"Executing {func.__name__}...")
        result = func(*args, **kwargs)
        end_time = time.time()
        print(f"{func.__name__} executed in {end_time - start_time:.4f} seconds")
        return result
    return wrapper