# 全局变量
ip = '192.168.13.98'
port = '3306'
class MySQL:__instance = Nonedef __init__(self, ip, port):self.ip = ipself.port = port@classmethoddef instance(cls, *args, **kwargs):if args or kwargs:cls.__instance = cls(*args, **kwargs)return cls.__instanceobj1 = MySQL.instance(ip, port)
obj2 = MySQL.instance()
obj3 = MySQL.instance()
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

<main.MySQL object at 0x058D6F30>
<main.MySQL object at 0x058D6F30> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL object at 0x058D6F30> {'ip': '192.168.13.98', 'port': '3306'}

def singlegon(cls):_instance = cls(ip, port)def wrapper(*args, **kwargs):if args or kwargs:return cls(*args, **kwargs)return _instancereturn wrapper@singlegon
class MySQL1:def __init__(self, ip, port):self.ip = ipself.port = portobj1 = MySQL1()
obj2 = MySQL1()
obj3 = MySQL1('1.1.1.3', 8080)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

<main.MySQL1 object at 0x04C102B0>
<main.MySQL1 object at 0x04C102B0> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL1 object at 0x04C10310> {'ip': '1.1.1.3', 'port': 8080}

class Mymetaclass(type):def __init__(self, class_name, class_bases, class_dic):super().__init__(class_name, class_bases, class_dic)self.__instance = self(ip, port)def __call__(self, *args, **kwargs):if args or kwargs:obj = self.__new__(self)self.__init__(obj, *args, **kwargs)self.__instance = objreturn self.__instanceclass MySQL2(metaclass=Mymetaclass):def __init__(self, ip, port):self.ip = ipself.port = portobj1 = MySQL2()
obj2 = MySQL2()
obj3 = MySQL2('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

<main.MySQL2 object at 0x04D003B0>
<main.MySQL2 object at 0x04D003B0> {'ip': '192.168.13.98', 'port': '3306'}
<main.MySQL2 object at 0x04D003D0> {'ip': '1.1.1.3', 'port': 80}

# instance.pyclass MySQL:def __init__(self, ip, port):self.ip = ipself.port = portip = '192.168.13.98'
port = 3306
instance = MySQL(ip, port)# 测试代码
import os, syssys.path.append(os.path.dirname(os.path.dirname(__file__)))
from test import instanceobj1 = instance.instance
obj2 = instance.instance
obj3 = instance.MySQL('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

<day30.instance.MySQL object at 0x052B0AB0>
<day30.instance.MySQL object at 0x052B0AB0> {'ip': '192.168.13.98', 'port': 3306}
<day30.instance.MySQL object at 0x052B03F0> {'ip': '1.1.1.3', 'port': 80}

class MySQL3(object):__instance = None__first_init = Truedef __init__(self, ip, port):if self.__first_init:self.ip = ipself.port = portself.__first_init = Falsedef __new__(cls, *args, **kwargs):if not cls.__instance:cls.__instance = object.__new__(cls)return cls.__instanceobj1 = MySQL3(ip, port)
obj2 = MySQL3(ip, port)
obj3 = MySQL3('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)

<main.MySQL3 object at 0x059603F0>
<main.MySQL3 object at 0x059603F0> {'ip': '192.168.13.98', 'port': '3306', '_MySQL3__first_init': False}
<main.MySQL3 object at 0x059603F0> {'ip': '192.168.13.98', 'port': '3306', '_MySQL3__first_init': False}