day30 singleton

Four ways to achieve Singleton

First, a static method within a class

IP = '127.0.0.1'
PORT = 3306

class MySQL:
    _instance = None
    def __init__(self, ip, port):
        self.ip = ip
        self.port = port
    
    @classmethod
    def from_conf(cls):
        if not _instance:
            cls._instance = cls(IP, PORT)
        return cls._instance

Second, the decorative implemented Singleton

def singleton(cls):
    cls.__instance = cls(IP, PORT)
    
    def wrapper(*args, **kwargs):
        if len(args) == 0 and kwargs == 0:
            return cls.__instance
        
        return cls(*args, **kwargs)
   
@singleton
class MySQL:
    def __init__(self, ip, port):
        self.ip = ip
        self.prot = port

Third, the single-mode embodiment metaclass

class Mymate(type):
    def __init__(self, name, bases, dic):
        self.__instance = self(IP, PORT)
    def __call__(self, *args, **kwargs):
        if len(args) == 0 and len(kwargs) == 0:
            return self.__instance
        obj = object.__new__(cls)
        obj.__init__(self, *args, **kwargs)
        return obj

Four, single-module introduced by way of embodiments

Your own brain supplement the implementation process

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