装饰器的应用场景-答应日志

• 参考链接： https://foofish.net/python-decorator.html

装饰器的应用场景

• 插入日志
• 性能测试
• 事务处理
• 缓存
• 权限校验

日志处理

• use_logging 不是代码逻辑函数，破坏代码结构；

def use_logging(func):
    logging.warn("{0} is running".formart(func.__name__))
    func()

def foo():
    print("I am foo")

use_logging(foo)

• 函数进入和退出被称为横切面，面向切面编程；
• 还是不友好，不简化；

def use_logging(func):
    def wrapper():
        logging.warn("{0}  is running ! ".format(func.__name__))
        return func()
    return wrapper

def foo():
    print('i am foo')
    
foo = use_logging(foo)
foo()

• 语法糖： 省略后面最后一步的赋值操作；

def use_logging(func):
    def wrapper():
        logging.warn("{0} is running.".format(func.__name__))
        return func()
    return wrapper

@use_logging
def foo():
    print("I am foo")

foo()

• 带参数的装饰器

import logging
def use_logging(level): # 接收装饰器的参数
    def decorator(func): # 返回函数 
        def wrapper(*args,**kwargs):  ## 接收主函数的参数
            if level == "warn":  # 装饰器需要干的事情
                logging.warning("{0} is running".format(func.__name__))
            if level == "info":
                logging.info("{0} is running...".format(func.__name__))
            return func(*args)
        return wrapper
    return decorator

@use_logging(level = "warn")
def foo(name = 'foo'):
    print(" i am {0}".format(name))
    
foo()

• 类装饰器

class Foo(object):
    def __init__(self,func):
        self._func = func
        
    def __call__(self):
        print('running...')
        self._func()
        print('ending...')
@Foo        
def bar():
    print('bar')
    
bar()