(python) three singleton patterns

#Method 1: Define a class method to implement the singleton pattern
import settings

class Mysql:
    __instance=None
    def __init__(self,host,port):
        self.host=host
        self.port=port

    @classmethod
    def singleton(cls):
        if not cls.__instance:
            cls.__instance=cls(settings.HOST,settings.PORT)
        return cls.__instance

obj1=Mysql('1.1.1.2',3306)
obj2=Mysql('1.1.1.3',3307)
print(obj1 is obj2) #False

obj3=Mysql.singleton()
obj4=Mysql.singleton()
print(obj3 is obj4) #True



#Method 2: Customize the metaclass to implement the singleton pattern
import settings

class Mymeta(type):
    def __init__(self,name,bases,dic): #Triggered when the class Mysql is defined

        # Take the configuration from the configuration file in advance to create an instance of Mysql
        self.__instance = object.__new__(self) # produce object
        self.__init__(self.__instance, settings.HOST, settings.PORT) # Initialize the object
        # The above two steps can be combined into the following step
        # self.__instance=super().__call__(*args,**kwargs)
        super().__init__(name,bases,dic)

    def __call__(self, *args, **kwargs): triggered when #Mysql(...)
        if args or kwargs: # There is a value in args or kwargs
            obj=object.__new__(self)
            self.__init__(obj,*args,**kwargs)
            return obj

        return self.__instance




class Mysql(metaclass=Mymeta):
    def __init__(self,host,port):
        self.host=host
        self.port=port

#
#
obj1=Mysql() # If no value is passed, the configuration is read from the configuration file to instantiate by default, all instances should point to a memory address
obj2=Mysql()
obj3=Mysql()

print(obj1 is obj2 is obj3)

obj4=Mysql('1.1.1.4',3307)
print(obj1 is obj4)


# Method 3: Define a decorator to implement the singleton pattern
import settings

def singleton(cls): #cls=Mysql
    _instance=cls(settings.HOST,settings.PORT)

    def wrapper(*args,**kwargs):
        if args or kwargs:
            obj=cls(*args,**kwargs)
            return obj
        return _instance

    return wrapper

@singleton # Mysql=Singleton(Mysql)
class Mysql:
    def __init__(self,host,port):
        self.host=host
        self.port=port

obj1=Mysql()
obj2=Mysql()
obj3=Mysql()
print(obj1 is obj2 is obj3) #True

obj4=Mysql('1.1.1.3',3307)
obj5=Mysql('1.1.1.4',3308)
print(obj3 is obj4) #Fals