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)