Python |集合1中的函数装饰器（简介）-yiteyi-C++库

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出身背景

在Python中，我们可以在另一个函数中定义一个函数。
在Python中，一个函数可以作为参数传递给另一个函数（一个函数也可以返回另一个函数）。

                     # A Python program to demonstrate that a function                   
                     # can be defined inside another function and a                   
                     # function can be passed as parameter.                   
                             
                     # Adds a welcome message to the string                   
                     def                               messageWithWelcome(                               str                               ):                   
                             
                                         # Nested function                   
                                         def                               addWelcome():                   
                                         return                               "Welcome to "                   
                             
                                         # Return concatenation of addWelcome()                   
                                         # and str.                   
                                         return                               addWelcome()                               +                               str                   
                             
                     # To get site name to which welcome is added                   
                     def                               site(site_name):                   
                                         return                               site_name                   
                             
                     print                               messageWithWelcome(site(                               "GeeksforGeeks"                               ))                   

输出：

Welcome to GeeksforGeeks

函数装饰器

我们使用@func_name指定要应用于另一个函数的装饰器。

                     # Adds a welcome message to the string                   
                     # returned by fun(). Takes fun() as                   
                     # parameter and returns welcome().                   
                     def                               decorate_message(fun):                   
                             
                                         # Nested function                   
                                         def                               addWelcome(site_name):                   
                                         return                               "Welcome to "                               +                               fun(site_name)                   
                             
                                         # Decorator returns a function                   
                                         return                               addWelcome                   
                             
                     @decorate_message                   
                     def                               site(site_name):                   
                                         return                               site_name;                   
                             
                     # Driver code                   
                             
                     # This call is equivalent to call to                   
                     # decorate_message() with function                   
                     # site("GeeksforGeeks") as parameter                   
                     print                               site(                               "GeeksforGeeks"                               )                   

输出：

Welcome to GeeksforGeeks

decorator在向函数附加数据（或添加属性）时也很有用。

                     # A Python example to demonstrate that                   
                     # decorators can be useful attach data                   
                             
                     # A decorator function to attach                   
                     # data to func                   
                     def                               attach_data(func):                   
                                         func.data                               =                               3                   
                                         return                               func                   
                             
                     @attach_data                   
                     def                               add (x, y):                   
                                         return                               x                               +                               y                   
                             
                     # Driver code                   
                             
                     # This call is equivalent to attach_data()                   
                     # with add() as parameter                   
                     print                               (add(                               2                               ,                               3                               ))                   
                             
                     print                               (add.data)                   