python进阶二：函数装饰器、类装饰器、如何保证原函数的元信息、装饰器嵌套、装饰器应用场景

装饰器

一、简单装饰器

def my_decorator(func): def wrapper(): print('wrapper of decorator!') func() return wrapper def greet(): print('halo world!') greet = my_decorator(greet) greet() # 输出 wrapper of decorator! hello world! @my_decorator def greet2(): print('halo world2!') greet2() # 输出 wrapper of decorator! hello world2!

这里my_decorator()为装饰器，将greet()包含在其中，改变了greet函数的行为，但是原函数greet并没变。不改变原函数的情况下，改变函数的行为。

调用方法：

1、像greet函数中进行调用

greet = my_decorator(greet) greet()

2、像greet2函数中进行调用 @my_decorator

这里的@称之为语法糖

二、带有参数的装饰器

def my_decorator(func): def wrapper(*args, **kwargs): print('wrapper of decorator!') func(*args, **kwargs) return wrapper @my_decorator def greet(message): print(message) greet('halo world!') # 输出 wrapper of decorator! halo world!

三、带有自定义参数的装饰器

举例：如果想让一个函数执行多次，可以写成

def repeat(num): def my_decorator(func): def wrapper(*args, **kwargs): for i in range(num): print('wrapper of decorator') func(*args, **kwargs) return wrapper return my_decorator @repeat(4) def greet(message): print(message) greet('hello world') # 输出： wrapper of decorator hello world wrapper of decorator hello world wrapper of decorator hello world wrapper of decorator hello world

四、原函数的元信息

greet.__name__ ## 输出 wrapper

以上可知，原函数元信息改变，greet函数被wrapper函数取代

解决：采用内置装饰器@functools.wraps(func)，将原函数的元信息拷贝到对应装饰器函数

import functools def my_decorator(func): @functools.wraps(func) def wrapper(*args, **kwargs): print('wrapper of decorator!') func(*args, **kwargs) return wrapper @my_decorator def greet(message): print(message) greet.__name__ # 输出 'greet'

五、类装饰器

主要依赖于函数_call_()

import time class TimeCount: def __init__(self, func): self.func = func def __call__(self, *args, **kwargs): start_time = time.time() self.func() end_time = time.time() print(f'执行函数时间为：{start_time-end_time}') @TimeCount def greet(): time.sleep(2) greet()

六、装饰器嵌套

@decorator1 @decorator2 @decorator3 def func(): ...

执行顺序：从里向外

decorator1(decorator2(decorator3(func))) import functools def my_decorator1(func): @functools.wraps(func) def wrapper(*args, **kwargs): print('execute decorator1') func(*args, **kwargs) return wrapper def my_decorator2(func): @functools.wraps(func) def wrapper(*args, **kwargs): print('execute decorator2') func(*args, **kwargs) return wrapper @my_decorator1 @my_decorator2 def greet(message): print(message) greet('hello world') # 输出 execute decorator1 execute decorator2 hello world

七、应用场景

身份认证、日志、缓存、输入合法性检查等