组团学

Python 装饰器

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一、装饰器概念

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()

二、简单装饰器

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()

三、复杂装饰器(带参数)

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))

四、通用装饰器

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

五、使用@符号装饰

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()

六、带参数的装饰器

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)

七、多个装饰器

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()

八、使用类实现装饰器

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

九、装饰器使用场景

  1. 参数、结果的检查
  2. 日志
  3. 缓存
  4. 权限管理
  5. 统计
  6. 计数
  7. 重试

十、统计函数执行次数

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()

十一、统计函数运行时间

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()

十二、retry装饰器

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")
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