# settings.py文件

IP = '1.1.1.1'

PORT = 3303

# 方式一：定义一个类方法实现单例模式

import settings

class People:

    __instance = None    #用于保存实例化的状态

    def __init__(self, ip, port):

        self.ip = ip

        self.port = port

    @classmethod

    def get(cls):

        if cls.__instance is None:

            cls.__instance = cls(settings.IP, settings.PORT)

        return cls.__instance

obj1 = People.get()

obj2 = People.get()

print(obj1)

print(obj2)

# <__main__.People object at 0x00000000021BA9B0>

# <__main__.People object at 0x00000000021BA9B0>

#方式二:定义一个装饰器实现单例模式

import settings

def singlet(cls):

    _instance = cls(settings.IP, settings.PORT)   #先实例化一个对象

    def wrapper(*args, **kwargs):

        if args or kwargs:

            obj = cls(*args, **kwargs)

            return obj        #有参数是返回后来实例化对象

        return _instance         #无参时，返回已经实例化好的对象

    return wrapper

@singlet    # MySQL=wrapper(MySQL)

class MySQL:

    def __init__(self, ip, port):

        self.ip = ip

        self.port = port

# 没有参数时，单例模式

obj1 = MySQL()

obj2 = MySQL()

obj3 = MySQL()

obj4 = MySQL('1.1.1.1', 3303)

print(obj1)

print(obj2)

print(obj3)

print(obj4)

# <__main__.MySQL object at 0x0000000001E6AA90>

# <__main__.MySQL object at 0x0000000001E6AA90>

# <__main__.MySQL object at 0x0000000001E6AA90>

# <__main__.MySQL object at 0x0000000001E6AB00>

#方式三：定制元类实现单例模式

import settings

class Mymeta(type):

    def __init__(self, class_name, class_bases, class_dic):

        instance = self(settings.IP, settings.PORT)

        self.__instance = instance

    def __call__(self, *args, **kwargs):         # self=MySQL

        if args or kwargs:          #  有参数执行下面的代码

            obj = self.__new__(self)          #创造一个空对象

            self.__init__(obj, *args, **kwargs)          #初始化

            return obj             #返回对象

        return self.__instance

class MySQL(metaclass=Mymeta):

    def __init__(self, ip, port):

        self.ip = ip

        self.port = port

obj1 = MySQL()

obj2 = MySQL()

obj3 = MySQL()

obj4 = MySQL('1.2.3.1', 3305)

print(obj1)

print(obj2)

print(obj3)

print(obj4)

# <__main__.MySQL object at 0x00000000021BAA90>

# <__main__.MySQL object at 0x00000000021BAA90>

# <__main__.MySQL object at 0x00000000021BAA90>

# <__main__.MySQL object at 0x00000000021BAB00>

方式四：利用模块导入实现单例模式

# singleton模块

import settings

class MySQL:

    def __init__(self, ip, port):

        self.ip = ip

        self.port = port

instance = MySQL(settings.IP, settings.PORT)

#单例模块

def f1():

    from singleton import instance

    print(instance)

def f2():

    from singleton import instance, MySQL

    print(instance)

    obj = MySQL('', 3302)

    print(obj)

f1()

f2()

# <singleton.MySQL object at 0x00000000021FAA90>

# <singleton.MySQL object at 0x00000000021FAA90>

# <singleton.MySQL object at 0x00000000021FA358>