Python – @Property & __attribute

測試環境為 CentOS 8 x86_64 (虛擬機)

使用 Property 時可以把 類別(Class) 的 方法 (Method) 轉變成存取 屬性 (Attribute) 包含 setter , getter 與 deleter 等方法 (Method) , 參考文章 – https://www.maxlist.xyz/2019/12/25/python-property/

使用 Property 時屬性 (Attribute) 通常使用 __attribute ( __double_leading_underscore ) 這種命名規則 ( 請參考 – https://benjr.tw/104282 ) 是不希望它被直接存取.

[root@localhost ~]# vi computer.py
class computer:
    def __init__(self):
        self.__CPU = 'Intel'

customer1 = computer()
print(customer1.CPU)

執行結果

[root@localhost ~]# python3 computer.py
Traceback (most recent call last):
  File "computer.py", line 6, in <module>
    print(customer1.CPU)
AttributeError: 'computer' object has no attribute 'CPU'

__attribute 屬性 (Attribute) 存取需透過 @Property 包含 setter , getter 與 deleter 等方法 (Method) 來存取.

• 範例: @Property 的使用與 getter.

  [root@localhost ~]# vi computer1.py
  class computer:
      def __init__(self):
          self.__CPU = 'Intel'
  
      @property
      def CPU(self):
          return self.__CPU
  
  customer1 = computer()
  print(customer1.CPU)
  customer1.CPU = 'AMD'
  

  執行結果

  [root@localhost ~]# python3 computer1.py
  Intel
  Traceback (most recent call last):
    File "computer1.py", line 11, in <module>
      customer1.CPU = 'AMD'
  AttributeError: can't set attribute
  

  說明:
  定義 computer 類別與初始化方法.

  class computer:
      def __init__(self):
          self.__CPU = 'Intel'
  

  並透過 @Property 把 CPU 類別(Class) 的 方法 (Method) 轉變成可讀取 __CPU 屬性 (Attribute) .

      @property
      def CPU(self):
          return self.__CPU
  

  建立 customer1 instance

  customer1 = computer()
  

  當讀取 Instance 的 CPU 屬性 customer1.CPU 時 是呼叫 CPU 方法(Method – def CPU(self) ),這方法為 CPU 屬性的 getter.

  print(customer1.CPU)
  

  執行結果

  Intel
  

  當我們要改變 Instance 的 CPU 屬性時卻生錯誤了,這是因為我們沒有定義 CPU 屬性相對應的 setter 才會出現錯誤.

  customer1.CPU = 'AMD'
  

  執行結果

  Traceback (most recent call last):
    File "computer1.py", line 11, in <module>
      customer1.CPU = 'AMD'
  AttributeError: can't set attribute
  

• 範例: 增加 Property 的 setter 與 deleter

  [root@localhost ~]# vi computer2.py
  class computer:
      def __init__(self):
          self.__CPU = 'Intel'
  
      @property
      def CPU(self):
          return self.__CPU
  
      @CPU.setter
      def CPU(self, value):
          self.__CPU = value
  
      @CPU.deleter
      def CPU(self):
          del self.__CPU
          print('del complete')
  
  customer1 = computer()
  print(customer1.CPU)
  customer1.CPU = 'AMD'
  print(customer1.CPU)
  del customer1.CPU
  

  執行結果

  [root@localhost ~]# python3 computer2.py 
  Intel
  AMD
  del complete
  

  說明:

  • getter
    執行

    print(customer1.CPU)
    

    呼叫

        @property
        def CPU(self):
            return self.__CPU
    

    結果

    Intel
    

  • setter
    執行 setter

    customer1.CPU = 'AMD'
    

    呼叫

        @CPU.setter
        def CPU(self, value):
            self.__CPU = value
    

    執行 getter

    print(customer1.CPU)
    

    呼叫

        @property
        def CPU(self):
            return self.__CPU
    

    執行結果

    AMD
    

  • deleter
    執行

    del customer1.CPU
    

    呼叫

        @CPU.deleter
        def CPU(self):
            del self.__CPU
            print('del complete')
    

    執行結果

    del complete