配置文件settings.py

IP='100.0.0.2'

PORT=3302

方式一：绑定给类的方法

class Mysql:

__instance = None

def __init__(self, ip, port):

self.ip = ip

self.port = port

@classmethod

def from_conf(cls):

if cls.__instance is None:

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

return cls.__instance

obj1 = Mysql.from_conf()

obj2 = Mysql.from_conf()

obj3 = Mysql.from_conf()

obj = Mysql('1.1.1.0', 3302)

print(obj)

print(obj1)

print(obj2)

print(obj3)

方式二：装饰器

def singleton(cls):

# 先造好一个空对象

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

def wrapper(*args, **kwargs):

if args or kwargs: # args 和 kwargs 有值时，返回obj

obj = cls(*args, **kwargs)

return obj

return instance

return wrapper

@singleton

class Mysql: # Mysql = singleton(Mysql)

def __init__(self, ip, port):

self.ip = ip

self.port = port

obj1 = Mysql() # wrapper()

obj2 = Mysql()

obj3 = Mysql()

obj4 = Mysql('1.1.1.2', 3303)

print(obj1)

print(obj2)

print(obj3)

print(obj4)

方式三：自定义元类

class Mymeta(type):

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

# 先造好一个空对象

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

def __call__(self, *args, **kwargs):

if args or kwargs:

# 拿到一个空对象

obj = self.__new__(self)

# 执行__init__方法为对象初始化属性

self.__init__(obj, *args, **kwargs)

# 返回一个实例化好的对象

return obj

return self.instance

class Mysql(metaclass=Mymeta):

def __init__(self, ip, port):

self.ip = ip

self.port = port

obj1 = Mysql() # 调用Mysql就是调用__call__方法

obj2 = Mysql()

obj3 = Mysql()

obj4 = Mysql('1.1.1.4', 3301)

print(obj1)

print(obj2)

print(obj3)

print(obj4)

方式四：利用模块的导入特性

importsettingsclassMysql:def __init__(self, ip, port):

self.ip=ip

self.port=port

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

singleton.py

def f1():

from singleton import instance

print(instance)

def f2():

from singleton import instance, Mysql

print(instance)

obj = Mysql('1.1.1.0', 3303)

print(obj)

f1()

f2()