python 装饰器

一、函数装饰器

1.从函数中返回函数

在 if/else 语句中我们返回 greet 和 welcome，而不是 greet() 和 welcome()。为什么那样？这是因为当你把一对小括号放在后面，这个函数就会执行；然而如果你不放括号在它后面，那它可以被到处传递，并且可以赋值给别的变量而不去执行它。 

def hi(name="yasoob"):
    def greet():
        return "now you are in the greet() function"
 
    def welcome():
        return "now you are in the welcome() function"
 
    if name == "yasoob":
        return greet
    else:
        return welcome
 
a = hi()
print(a)
#outputs: <function greet at 0x7f2143c01500>
 
#上面清晰地展示了`a`现在指向到hi()函数中的greet()函数
#现在试试这个
 
print(a())
#outputs: now you are in the greet() function

2.装饰器

用函数decorator装饰function_requiring_decoration函数

import time
def decorator(func):
    def decorator_function():
        localtime = time.asctime(time.localtime(time.time()))
        print('before decorator running,time is', localtime)
        func()
        localtime = time.asctime(time.localtime(time.time()))
        print('after decorator running,time is ', localtime)
    #必须返回函数名，不带括号
    return decorator_function


def function_requiring_decoration():
    a, b = 5, 3
    time.sleep(1)
    print("The result is ", a + b)

function__decoration = decorator(function_requiring_decoration)

if __name__=="__main__":
    function__decoration()

以上代码的简写

import time
def decorator(func):
    def decorator_function():
        localtime = time.asctime(time.localtime(time.time()))
        print('before decorator running,time is', localtime)
        func()
        localtime = time.asctime(time.localtime(time.time()))
        print('after decorator running,time is ', localtime)
    #fanhuihans,bujiakuohao
    return decorator_function

@decorator
def function_requiring_decoration():
    a, b = 5, 3
    time.sleep(1)
    print("The result is ", a + b)

if __name__=="__main__":
    function_requiring_decoration()

结果

before decorator running,time is Wed Jan 20 20:07:03 2021
The result is  8
after decorator running,time is  Wed Jan 20 20:07:04 2021

二、类装饰器

import time

class Decorator(object):
    def __init__(self, func):
        self.func = func
    def call(self):
        localtime = time.asctime(time.localtime(time.time()))
        print ('before decorator running,time is',localtime)
        self.func() #run add function
        localtime = time.asctime(time.localtime(time.time()))
        print ('after decorator running,time is ',localtime)

@Decorator
def add():
    a,b=5,3
    time.sleep(1)
    print ("The result is ",a+b)
if __name__=="__main__":
    add.call()

结果，如上代码就完成了一个类装饰器的功能，给运行的函数添加了时间日志

before decorator running,time is Wed Jan 20 19:58:41 2021
The result is  8
after decorator running,time is  Wed Jan 20 19:58:42 2021