Python 装饰器

194次阅读

共计 3524 个字符，预计需要花费 9 分钟才能阅读完成。

概念：是一个闭包，把一个函数作为参数然后返回一个替代版的函数，本质上是一个返回函数的函数

作用：在不修改原函数的前提下增加函数的功能，最好使用装饰器

def say():
    print("zutuanxue_com is a good man")

def newSay():
    print("**************")
    say()

newSay()

装饰器实现不修改原函数而增加新的功能

# 参数 f：要给哪个函数增加功能，那么就在调用 wrapper() 函数时传递那个函数 
def wrapper(f):
    # inner() 函数即为替代版函数，要实现原函数的功能，并增加新功能 
    def inner():
        # 在原函数基础上增加新的功能 
        print("*************")
        # 实现原函数功能 
        res = f()
        return res
    return inner

def say():
    print("zutuanxue_com is a good man")

# newSay = wrapper(say)
# newSay()

say = wrapper(say)
say()

def wrapper(f):
    # 原函数的参数在 inner 函数这里传递 
    def inner(name, age):
        # 增加的判断 age 的功能 
        if age < 0:
            age = 0
        res = f(name, age)
        return res
    return inner

def say(name, age):
    return "%s is a good man!He is %d years old!"%(name, age)

say = wrapper(say)
# 增加判断年龄如果小于 0，则打印 0 即可 
print(say("zutuanxue_com", -18))

def wrapper1(f):
    def inner(name, age):
        if age < 0:
            age = 0
        res = f(name, age)
        return res
    return inner
def wrapper2(f):
    def inner(name, age, height):
        if age < 0:
            age = 0
        res = f(name, age, height)
        return res
    return inner
def wrapper3(f):
    def inner(name, age, *args, **kwargs):
        if age < 0:
            age = 0
        res = f(name, age, *args, **kwargs)
        return res
    return inner
  
  
def say1(name, age):
    return "%s is a good man!He is %d years old!"%(name, age)

def say2(name, age, height):
    return "%s is a good man!He is %d years old!His height is %.2f"%(name, age, height)

# 装饰函数 
say1 = wrapper3(say1)
say2 = wrapper3(say2)
print(say1("zutuanxue_com", -19))
print(say2("kaige", -20, 173.55))

# 给函数增加打印一串星号的功能，通用所有函数 
def wrapper(f):
    def inner(*args, **kwargs):
        print("*************")
        res = f(*args, **kwargs)
        return res
    return inner

python2.4 开始支持使用 @符号将装饰器应用到函数上，只需要在函数定义时加上 ”@装饰器名称 ” 即可完成装饰操作

def wrapper(f):
    def inner():
        print("*************")
        res = f()
        return res
    return inner

@wrapper  #相当于   say = wrapper(say)
def say():
    print("zutuanxue_com is a good man")

say()

规定函数执行次数

# 接收装饰器传递的参数 
def wrapper(count=3):
    # 接收带添加功能的函数 
    def deco(f):
        # 接收原函数的参数 
        def inner(*args, **kwargs):
            for i in range(count):
                f(*args, **kwargs)
        return inner
    return deco

# 没有参数传递，也需要带着小括号 
@wrapper()
def say(name, age):
    print("%s is a good man!He is %d years old!"%(name, age))

say("zutuanxue_com", 18)

def wrapper1(f):
    def inner1(*args, **kwargs):
        print("enter inner1")
        res = f(*args, **kwargs)
        print("exit inner1")
        return res
    return inner1
def wrapper2(f):
    def inner2(*args, **kwargs):
        print("enter inner2")
        res = f(*args, **kwargs)
        print("exit inner2")
        return res
    return inner2
def wrapper3(f):
    def inner3(*args, **kwargs):
        print("enter inner3")
        res = f(*args, **kwargs)
        print("exit inner3")
        return res
    return inner3

'''
装饰时：从距离近的装饰器开始装饰
执行时：从距离远的装饰器内部函数开始执行
'''
@wrapper1
@wrapper2
@wrapper3
def say():
    print("zutuanxue_com is a good man")
    
'''
say = wrapper3(say)
say = wrapper2(say)
say = wrapper1(say)
---------------------------
inner3 = wrapper3(say)
say = inner3
inner2 = wrapper2(inner3)
say = inner2
inner1 = wrapper1(inner2)
say = inner1
'''
print("-------------------------")
say()

以上的装饰器均由函数实现的，也可以使用类来实现装饰器，后面讲

参数、结果的检查
日志
缓存
权限管理
统计
计数
重试

def wrapper(f):
    count = 1
    def inner(*args, **kwargs):
        nonlocal count
        print("第 %d 次执行"%(count))
        res = f(*args, **kwargs)
        count += 1
        return res
    return inner

@wrapper
def say():
    print("zutuanxue_com is a good man")

say()
say()
say()

import time

def wrapper(f):
    def inner(*args, **kwargs):
        t1 = time.time() # 获取当前时间的时间戳 
        res = f()
        t2 = time.time()
        print("耗时 %.2f 秒"%(t2-t1))
        return res
    return inner

@wrapper
def say():
    print("zutuanxue_com is a good man")
    # 休息 2 秒钟，可以是浮点数 
    time.sleep(2)
    print("zutuanxue_com is a nice man")

say()

import random
import time

def retry(count=3, wait=0, exceptions=(Exception,)):
    def deco(f):
        def inner(*args, **kwargs):
            for i in range(count):
                try:
                    res = f(*args, **kwargs)
                    return res
                except exceptions as e:
                    if not (i == count - 1):
                        time.sleep(wait)
            return -1 # 这里用的表示失败的值一定不能出现在成功中 
        return inner
    return deco

@retry()
def func():
    num = random.choice([1,2,3,4])
    if num <= 2:
        num / 0
    else:
        print("********************", num)

if func() == -1:
    print("程序运行出错")