python 单例模式

class SingleObj():
    __singleobj=None
    @classmethod
    def get_singleinstance(cls):
        if not cls.__singleobj:
            cls.__singleobj=SingleObj()
        return cls.__singleobj
obj1=SingleObj.get_singleinstance()
print(obj1)        
obj2=SingleObj.get_singleinstance()
print(obj2)
obj3=SingleObj.get_singleinstance()
print(obj3)
##ret
<__main__.SingleObj instance at 0x00000000057B1E88>
<__main__.SingleObj instance at 0x00000000057B1E88>
<__main__.SingleObj instance at 0x00000000057B1E88>