Python single-instance mode

Directly on the code:

classSingleton (object):def __new__(self):if  notHasattr (Self,'instance'): Self.instance= Super (Singleton, self).__new__(self) self.num= 1returnself.instancedefAdd (self): Self.num+ = 1defHello (self):Print(self.num) S1=Singleton () S1.add () S1.hello ( )2S2=Singleton () S2.hello ( )2

This is the perfect example of the 13th page of Python design mode.
Special Note:
1, there are netizens said __new__ is called before the __init__ instantiation method, parameters must use the CLS, and can not use self, after testing, but can use self;
2, if the attribute num is initialized in __init__, the singleton mode cannot be implemented, and NUM will be initialized each time the object is created;

Python single-instance mode