Python 30 单例模式

单例模式

多次实例化的结果指向同一个实例

单例模式实现方式

 import settings

 #方式一：
 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()
 obj4=MySQL('1.1.1.3',3309)
 print(obj1)
 print(obj2)
 print(obj3)

1 import settings
2
3 #方式二：
4 def singleton(cls):
5       __instance=cls(settings.IP,settings.PORT)
6       def wrapper(*args,**kwargs):
7             if len(args) !=0 or len(kwargs) !=0:
8                  obj=cls(*args,**kwagrs)
9                   return obj
10             return __instance
11       return wrappers
12
13 @singleton
14 class MySQL:
15      def __init__(self,ip,port)
16           self.ip=ip
17           self.port=port
18
19 obj1=MySQL.from_conf()
20 obj2=MySQL.from_conf()
21 obj3=MySQL.from_conf()
22 obj4=MySQL('1.1.1.3',3309)
23 print(obj1)
24 print(obj2)
25 print(obj3)
26 print(obj4)

 import settings

 #实例三

 class Mymeta(type):
      def __init__(self,class_name,class_bases,class_dic):
             #self=MySQL这个类
             self.__instance=self(settings.IP,settings.OPRT)

     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):#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)

 1 #实例四
 2
 3 def f1():
 4       from singleton import intance
 5       print(instance)
 6
 7 def f2():
 8       from singleton import instance,MySQL
 9       print(instance)
10       obj=MySQL('1.1.1.3',3302)
11       print(obj)
12
13 f1()
14 f2()
15
16 #该方法还需创建一个 singleton.py 的文件，内容如下：
17
18 import settings
19
20 class MySQL:
21      print('run...')
22      def __init__(self,ip,port):
23            self.ip=ip
24            self.port=port
25
26 instance=MySQL(settings.IP,settings.PORT)