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Python-設計模式-單例模式

Python
設計模式
單例模式

Lazy初始化，指行緒不安全

class Singleton(object): 
   _instance = None
   def __new__(cls, *args, **kw):
      if not cls._instance: 
         cls._instance = super(Singleton, cls).__new__(cls, *args, **kw) 
         return cls._instance 

 class MyClass(Singleton): 
   a = 1 

 one = MyClass() 
two = MyClass() 
one == two 

沒Lazy初始化，指行緒安全

class Singleton1(object): 
   pass 

 class Singleton2(Singleton1): 
   __instance = Singleton1() 
   def __new__(cls, *args, **kw): 
      return cls.__instance 
class MyClass2(Singleton2): 
   a = 2 

 new_one = MyClass2()
new_two = MyClass2()

new_two == new_two 

程式碼說明

每個範例最後一行都是確認兩者是否相同
第一個範例用了if判斷_instance是否為空值，如果是，則實作物件，為Lazy初始化
第一個範例先定義singleton1，在singleton2直接實作在_instance，這是模仿java的做法，不確定執行緒安全與否。

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