python裝飾器基礎及應用

一、簡介

裝飾器是是修改其它函數功能的函數；其意義是讓其他函數在不修改任何代碼的前提下增加額外功能

 

 

二、數據類型

 

首先我們來看一段簡單的代碼：

from types import MethodType,FunctionType

class A(object):
    def f1(self):
        pass


def f2(a, b):
    return a + b

if __name__ == '__main__':
    a = A()
    print(type(a.f1))   #<class 'method'>
    print(type(f2))    #<class 'function'>

結論：不難看出，f1的類型是方法，f2的類型是函數；那有人會問了解這個有啥作用呢？其實了解這個有助於我們下面了解裝飾器的原理

 

 

三、認識裝飾器：

 

let’s go… 我們來看一個案例：

def B():
    print("now you are inside the B() function")
    
    
    def sing():
        return "now you are in the sing() function"
    
    
    def eat():
        return "now you are in the eat() function"
    
    
    def sleep():
        return "now you are in the sleep() function"
    
    print(sing())
    print(eat())
    print(sleep())
#輸出的結果為：
now you are inside the hi() function
now you are in the sing() function
now you are in the eat() function
now you are in the sleep() function

 

結論：那現在我們知道了可以在函數中定義另外的函數。也就是說：我們可以創建嵌套的函數

 

我們再接着看一段代碼，如何讓函數作為參數傳給另外一個函數的：

def A():
    return "hi 小陳!"

def doSomethingBeforeA(func):
    print("I am doing some boring work before executing A()")
    print(func())

#執行：
doSomethingBeforeA(A)
#輸出結果：
I am doing some boring work before executing A()
hi 小陳!

 

 

 什麼？你還沒看懂，那我們再看一個案例：

 

from types import FunctionType

def text():
    return "Hello world！"

def add_itali(func: FunctionType):
    def new_func():
        #print("now you are in the new_func() function")
        return text()   #返回text()函數
    return new_func

#執行：
print(type(add_itali(text)))  
print(add_itali(text)())  
#輸出結果：
<class 'function'>
Hello world！

 

難么現在你看懂了么？如果還是沒懂，沒關係我們再來看看下一段代碼：

def new_decorator(func):
    def wrapTheFunction():
        print("I am doing some boring work before executing func()")
        func()
        print("I am doing some boring work after executing func()")
    return wrapTheFunction

def requiring_decoration():
    print("I am the function which needs  decoration")


#執行：
requiring_decoration()

#輸出結果：
I am the function which needs  decoration
#執行：
new_decorator(requiring_decoration)()

#輸出結果：
I am doing some boring work before executing func()
I am the function which needs  decoration
I am doing some boring work after executing func()

有人會有疑問，new_decorator(requiring_decoration)（）為哈後面要加「()」呢去，請繼續往下看：

#執行：
print(new_decorator(requiring_decoration))

#輸出結果：
function new_decorator.<locals>.wrapTheFunction at 0x000001FC976BB620>

為什麼會這樣呢，請隨我娓娓道來。。。

 

 

 

四、裝飾器的優雅使用：

 

那麼好，我們把上面代碼再優化下，用裝飾器常用的表達方式表示出來：

def new_decorator(func):
    def wrapTheFunction():
        print("I am doing some boring work before executing func()")
        func()  #被裝飾的函數
        print("I am doing some boring work after executing func()")
    return wrapTheFunction

@new_decorator
def requiring_decoration():
    print("I am the function which needs  decoration")
#執行：
requiring_decoration()

#輸出結果：
I am doing some boring work before executing func()
I am the function which needs  decoration
I am doing some boring work after executing func()

老鐵們，現在你們懂了么,沒懂我們再來看一段代碼：

#需求：  <b><i> Hello World!</i></b>
from types import FunctionType

def add_bold(func: FunctionType):
    def new_func():
        return f"<b>{func()}</b>"
    return new_func

def add_itali(func: FunctionType):
    def new_func():
        return f"<i>{func()}</i>"
    return new_func

@add_itali  # 語法
@add_bold
def text():
    return "Hello world！"
#執行：
print(text())

#輸出結果：
<i><b>Hello world！</b></i>

 

 

五、總結：

 

#語法：裝飾器就是一個函數
def 裝飾器名(func):
      def wrapper(*args, **kwargs):
             // 要做的裝飾 ，，省略若干代碼
             result = func(*args,**kwargs)
             return result
      return wrapper

 

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