单例模式:多次实例化的结果指向同一个实例
实现方式 一、使用类方法(调用创新对象,函数返回原定对象)
import settings
class Mysql:
__instance = None
def __init__(self, host, port):
self.host = host
self.port = port
@classmethod
def singleton(cls):
if not cls.__instance:
# 创建类实例存入局部空间
cls.__instance = cls(settings.IP, settings.PORT)
return cls.__instance
# 使用init创建实例
obj1 = Mysql('1.1.1.2', 3306)
obj2 = Mysql('1.1.1.3', 3307)
print(obj1 is obj2) # False
# 使用类方法创建实例
obj3 = Mysql.singleton()
obj4 = Mysql.singleton()
print(obj3 is obj4) # True
import settings class Mysql: __instance = None def __init__(self, host, port): self.host = host self.port = port @classmethod def singleton(cls): if not cls.__instance: # 创建类实例存入局部空间 cls.__instance = cls(settings.IP, settings.PORT) return cls.__instance # 使用init创建实例 obj1 = Mysql('1.1.1.2', 3306) obj2 = Mysql('1.1.1.3', 3307) print(obj1 is obj2) # False # 使用类方法创建实例 obj3 = Mysql.singleton() obj4 = Mysql.singleton() print(obj3 is obj4) # True
实现方式 二、定义装饰器(有参创建新对象,无参返回原对象)
import settings def singleton(cls): _instance=cls(settings.IP,settings.PORT) def wrapper(*args,**kwargs): if len(args) !=0 or len(kwargs) !=0: obj=cls(*args,**kwargs) return obj return _instance return wrapper @singleton #MySQL=singleton(MySQL) #MySQL=wrapper class MySQL: def __init__(self, ip, port): self.ip = ip self.port = port # obj=MySQL('1.1.1.1',3306) #obj=wrapper('1.1.1.1',3306) # print(obj.__dict__) obj1=MySQL() #wrapper() obj2=MySQL() #wrapper() obj3=MySQL() #wrapper() obj4=MySQL('1.1.1.3',3302) #wrapper('1.1.1.3',3302) print(obj1) print(obj2) print(obj3) print(obj4)
实现方式 三、元类实现(有参创建新对象,无参返回原对象)
import settings
class Mymeta(type):
def __init__(self,class_name,class_bases,class_dic):
#self=MySQL这个类
self.__instance=self(settings.IP,settings.PORT)
def __call__(self, *args, **kwargs):
# self=MySQL这个类
if len(args) != 0 or len(kwargs) != 0:
obj=self.__new__(self)
self.__init__(obj,*args, **kwargs)
return obj
else:
return self.__instance
class MySQL(metaclass=Mymeta): #MySQL=Mymeta(...)
def __init__(self, ip, port):
self.ip = ip
self.port = port
obj1=MySQL()
obj2=MySQL()
obj3=MySQL()
obj4=MySQL('1.1.1.3',3302)
print(obj1)
print(obj2)
print(obj3)
print(obj4)
import settings class Mymeta(type): def __init__(self,class_name,class_bases,class_dic): #self=MySQL这个类 self.__instance=self(settings.IP,settings.PORT) def __call__(self, *args, **kwargs): # self=MySQL这个类 if len(args) != 0 or len(kwargs) != 0: obj=self.__new__(self) self.__init__(obj,*args, **kwargs) return obj else: return self.__instance class MySQL(metaclass=Mymeta): #MySQL=Mymeta(...) def __init__(self, ip, port): self.ip = ip self.port = port obj1=MySQL() obj2=MySQL() obj3=MySQL() obj4=MySQL('1.1.1.3',3302) print(obj1) print(obj2) print(obj3) print(obj4)
实现方式 四、模块实现
配置文件settings
IP = '192.168.1.1' PORT = 3306
-模块文件 singleton
import settings class MySQL: print('run....') def __init__(self, ip, port): self.ip = ip self.port = port instance = MySQL(settings.IP, settings.PORT)
-执行文件
def f1(): from singleton import instance print(instance) def f2(): from singleton import instance,MySQL print(instance) obj = MySQL('1.1.1.3',3302) print(obj) f1() f2()