python 的单例

例子

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()
print(one == two)
print(one is two)
print(id(one), id(two))

输出

True
True                                                        
499807697384 499807697384                                   
[Program finished]

例子

class test(object):
    _a=None
    def __init__(self):
        self.b=2
    def __new__(cls,*args,**kargs):
        if(not cls._a):
            cls._a=super(test,cls).__new__(cls,*args,**kargs)
        return cls._a
        

x=test()
print(x)
print(x.b)
y=test()
print(y)
print(y.b)

输出

<__main__.test object at 0x716e0fb9e8>
2                                                           
<__main__.test object at 0x716e0fb9e8>                      
2                                                           
[Program finished]