我又浪回来了，Pyhton设计模式之实现单例模式的N种方法

°蓝鲤歌蓝

各位小伙伴去面试时很有可能会被问到单例模式如何实现，现在就一起来看看吧。

1. # -*-coding:utf-8-*-
   
2. 
   
3. __Author__ = "Mr.D"
   
4. __Date__ = '2019\1\27 0027 7:36'
   
5. 
   
6. # __new__ 实现单例
   
7. class Singleton():
   
8.     _instance = None
   
9. 
   
10.     def __new__(cls, *args, **kwargs):
    
11.         if not cls._instance:
    
12.             cls._instance = super(Singleton, cls).__new__(cls)
    
13.         return cls._instance
    
14. 
    
15. 
    
16. s1 = Singleton()
    
17. s2 = Singleton()
    
18. print(s1 is s2)
    
19. 
    
20. 
    
21. # 装饰器实现单例
    
22. def Single(cls):
    
23.     _instance = {}
    
24. 
    
25.     def inner():
    
26.         if cls not in _instance:
    
27.             _instance[cls] = cls()
    
28. 
    
29.         return _instance[cls]
    
30. 
    
31.     return inner
    
32. 
    
33. 
    
34. @Single
    
35. class Singleton1():
    
36.     pass
    
37. 
    
38. 
    
39. s1 = Singleton1()
    
40. s2 = Singleton1()
    
41. print(s1 is s2)
    
42. 
    
43. 
    
44. # 元类实现单例
    
45. class Metaclass(type):
    
46.     _instance = {}
    
47. 
    
48.     def __call__(cls, *args, **kwargs):
    
49.         if cls not in cls._instance:
    
50.             cls._instance[cls] = super().__call__()
    
51. 
    
52.         return cls._instance[cls]
    
53. 
    
54. 
    
55. class Singleton2(metaclass=Metaclass):
    
56.     pass
    
57. 
    
58. 
    
59. s1 = Singleton2()
    
60. s2 = Singleton2()
    
61. print(s1 is s2)
    
62. 
    
63. 
    
64. # 类方法实现单例
    
65. class Singleton3():
    
66.     _instance = None
    
67. 
    
68.     @classmethod
    
69.     def getInstance(cls):
    
70.         if not cls._instance:
    
71.             cls._instance = Singleton3()
    
72.         return cls._instance
    
73. 
    
74. 
    
75. s1 = Singleton3.getInstance()
    
76. s2 = Singleton3.getInstance()
    
77. print(s1 is s2)
    
78. 
    
79. 
    
80. # 特殊的单例：单态模式
    
81. class Singleton4():
    
82.     _shared_state = {}
    
83. 
    
84.     def __new__(cls, *args, **kwargs):
    
85.         obj = super().__new__(cls, *args, **kwargs)
    
86.         obj.__dict__ = cls._shared_state
    
87.         return obj
    
88. 
    
89. 
    
90. s1 = Singleton4()
    
91. s2 = Singleton4()
    
92. s1.x = 5
    
93. print(s2.x)
    
94. 
    
95. 
    
96. # 类装饰器实现单例
    
97. class Single1():
    
98.     def __init__(self, cls):
    
99.         self._cls = cls
    
100.         self._instance = {}
     
101. 
     
102.     def __call__(self, *args, **kwargs):
     
103.         _cls = self._cls
     
104.         _instance = self._instance
     
105.         print(_instance)
     
106.         if _cls not in _instance:
     
107.             print(f'myinstance is {_instance}')
     
108.             _instance[self._cls] = _cls()
     
109. 
     
110.         return _instance[self._cls]
     
111. 
     
112. 
     
113. class Singleton5():
     
114.     pass
     
115. 
     
116. s1 = Singleton4()
     
117. s2 = Singleton4()
     
118. print(s1 is s2)
     

复制代码

°蓝鲤歌蓝

有不明白的可以在评论里详细说明，我会统一回复。

幽梦三影

666，只写过第一种，学习一下

塔利班

应用场景是什么，，从来没接触过

°蓝鲤歌蓝

塔利班 发表于 2019-1-29 09:19
应用场景是什么，，从来没接触过

资源共享的场景，比如日志文件或者应用配置文件等。

塔利班

°蓝鲤歌蓝 发表于 2019-2-21 21:49
资源共享的场景，比如日志文件或者应用配置文件等。

面试如何

四点好

记号一下，现在看着还是很累啊。