29. python装饰器

装饰器

类似于java的切面， 再不更改原函数代码的前提下，动态做一些动作。

一. 简单的装饰器

def logging(func):

    def wrapper(*args, **kwargs):
        print("logging is running",file=sys.stderr)
        func(*args, **kwargs)
    return wrapper

def bar():
    print('i am bar')

bar= logging(bar)# 返回wrapper函数
bar() # 调用返回的wrapper，内部会执行bar()

上面其实就是装饰器的本质， 为了隐藏
b= logging(bar)
b()
这种丑陋的写法我们可以写成如下的样子

def logging(func):

    def wrapper(*args, **kwargs):
        print("logging is running",file=sys.stderr)
        func(*args, **kwargs)
    return wrapper

@logging
def bar():
    print('i am bar')
bar() 

二. 带参数的装饰器

• 传统写法

import sys


def use_logging(level):
    def decorator(func):
        def wrapper(*args):
            if level == "warn":
                print("logging is running",file=sys.stderr)
            else:
                print("logging is running",file=sys.stdout)
            func(*args)
        return wrapper

    return decorator

# @use_logging(level="warn")
def foo(name):
    print("i am %s" % name)

d = use_logging("warn")
f = d(foo)
f("董梦雨")

• 装饰器高级写法

import sys


def logging(level):
    def decorator(func):
        def wrapper(*args):
            if level == "warn":
                print("logging is running",file=sys.stderr)
            else:
                print("logging is running",file=sys.stdout)
            func(*args)
        return wrapper

    return decorator

@logging(level="warn")
def foo(name):
    print("i am %s" % name)

foo("董梦雨")