python 的单例

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))

True
True                                                        
499807697384 499807697384                                   
[Program finished]