day04.4-装饰器

1. 装饰器

• 装饰器本身就是函数，功能是为其他函数添加附加功能
• 装饰器的设计原则：

(a). 不修改被修饰函数的源代码；

(b). 不修改被修改函数的调用方法。

• 装饰器=高阶函数+函数嵌套+闭包
• 装饰器框架

 def timmer(func):
     def wrapper():
         func()
     return wrapper
 func = timmer()
 func()

2. 装饰器实例1：计算被修饰函数的运行时间

 import time
 def bin(name,age):
     time.sleep(3)
     print("I am %s, I am %s years old" %(name,age))
     time.sleep(3)
 def timer(func):
     def wrapper(*args,**kwargs):
         star = time.time()
         func(*args,**kwargs)
         stop = time.time()
         res = stop-star
         return res
     return wrapper
 bin = timer(bin)        #相当于wrapper = timer(bin)
 dif_time = bin("alex",18)        #相当于dif_time = wrapper("alex",18)
 print("被修饰函数的运行时间为%s" %dif_time)

 """
 运行结果：
     I am alex, I am 18 years old
     被修饰函数的运行时间为6.001323223114014
 """ 

3. 装饰器实例2：登录界面添加身份认证功能

 user_list = [{"name":"stephen","passwd":""},
              {"name": "klay", "passwd": ""},
              {"name": "durant", "passwd": ""},
              {"name": "green", "passwd": ""}]
 def home(name):
     print("Welcome %s to enter the system" %name)
 def certification(func):
     def wrapper(name):
         passwd = input("please enter your password:").strip()
         for item in user_list:
             if item["name"]==name and item["passwd"]==passwd:
                 func(name)
                 return 1
         return 0
     return wrapper
 home = certification(home)    #相当于wrapper = certification(home)
 res = home("klay")      #相当于wrapper("klay")
 if not res:
     print("密码或用户名输入错误")

 """
 运行结果：
     please enter your password:123
     Welcome klay to enter the system
 """