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
import settings class Mysql:
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()