本文着重讲解了python 实现单例模式的5种方法，有助于更直观的学习和测试python 设计模式，欢迎大家阅读
一、classmethod装饰器
# 全局变量
ip = '192.168.13.98'
port = '3306'
class MySQL:
__instance = None
def __init__(self, ip, port):
self.ip = ip
self.port = port
@classmethod
def instance(cls, *args, **kwargs):
if args or kwargs:
cls.__instance = cls(*args, **kwargs)
return cls.__instance
obj1 = MySQL.instance(ip, port)
obj2 = MySQL.instance()
obj3 = MySQL.instance()
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
输出结果
<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'}
二、类的装饰器
def singlegon(cls):
_instance = cls(ip, port)
def wrapper(*args, **kwargs):
if args or kwargs:
return cls(*args, **kwargs)
return _instance
return wrapper
@singlegon
class MySQL1:
def __init__(self, ip, port):
self.ip = ip
self.port = port
obj1 = MySQL1()
obj2 = MySQL1()
obj3 = MySQL1('1.1.1.3', 8080)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
运行结果
<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}
三、元类
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 = obj
return self.__instance
class MySQL2(metaclass=Mymetaclass):
def __init__(self, ip, port):
self.ip = ip
self.port = port
obj1 = MySQL2()
obj2 = MySQL2()
obj3 = MySQL2('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
运行结果
<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}
四、模块导入
# instance.py
class MySQL:
def __init__(self, ip, port):
self.ip = ip
self.port = port
ip = '192.168.13.98'
port = 3306
instance = MySQL(ip, port)
# 测试代码
import os, sys
sys.path.append(os.path.dirname(os.path.dirname(__file__)))
from test import instance
obj1 = instance.instance
obj2 = instance.instance
obj3 = instance.MySQL('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
运行结果
<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}
五、重写__new__()
class MySQL3(object):
__instance = None
__first_init = True
def __init__(self, ip, port):
if self.__first_init:
self.ip = ip
self.port = port
self.__first_init = False
def __new__(cls, *args, **kwargs):
if not cls.__instance:
cls.__instance = object.__new__(cls)
return cls.__instance
obj1 = MySQL3(ip, port)
obj2 = MySQL3(ip, port)
obj3 = MySQL3('1.1.1.3', 80)
print(obj1)
print(obj2, obj2.__dict__)
print(obj3, obj3.__dict__)
运行结果
<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}
注：前四种可以实现单例模式，但都不是绝对单例模式，可以创建新的对象，但是第五种方式是绝对单例模式，全局只能真正创建一次对象
