python 四种单例模式
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python 四种单例模式
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1
2 1 使用__new__方法
3 Python
4 class Singleton(object): def __new__(cls, *args, **kw): if not hasattr(cls, '_instance'): orig = super(Singleton, cls) cls._instance = orig.__new__(cls, *args, **kw) return cls._instanceclass MyClass(Singleton): a = 1
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10 class Singleton(object):
11 def __new__(cls, *args, **kw):
12 if not hasattr(cls, '_instance'):
13 orig = super(Singleton, cls)
14 cls._instance = orig.__new__(cls, *args, **kw)
15 return cls._instance
16
17 class MyClass(Singleton):
18 a = 1
19 2 共享屬性
20 創(chuàng)建實例時把所有實例的__dict__指向同一個字典,這樣它們具有相同的屬性和方法.
21
22 Python
23 class Borg(object): _state = {} def __new__(cls, *args, **kw): ob = super(Borg, cls).__new__(cls, *args, **kw) ob.__dict__ = cls._state return obclass MyClass2(Borg): a = 1
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29
30 class Borg(object):
31 _state = {}
32 def __new__(cls, *args, **kw):
33 ob = super(Borg, cls).__new__(cls, *args, **kw)
34 ob.__dict__ = cls._state
35 return ob
36
37 class MyClass2(Borg):
38 a = 1
39 3 裝飾器版本
40 Python
41 def singleton(cls, *args, **kw): instances = {} def getinstance(): if cls not in instances: instances[cls] = cls(*args, **kw) return instances[cls] return getinstance@singletonclass MyClass: ...
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48 def singleton(cls, *args, **kw):
49 instances = {}
50 def getinstance():
51 if cls not in instances:
52 instances[cls] = cls(*args, **kw)
53 return instances[cls]
54 return getinstance
55
56 @singleton
57 class MyClass:
58 ...
59 4 import方法
60 作為python的模塊是天然的單例模式
61
62 Python
63 # mysingleton.pyclass My_Singleton(object): def foo(self): passmy_singleton = My_Singleton()# to usefrom mysingleton import my_singletonmy_singleton.foo()
64
65
66
67 # mysingleton.py
68 class My_Singleton(object):
69 def foo(self):
70 pass
71
72 my_singleton = My_Singleton()
73
74 # to use
75 from mysingleton import my_singleton
76
77 my_singleton.foo()
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轉(zhuǎn)載于:https://www.cnblogs.com/chengyunshen/p/7196280.html
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