day29单例模式的4种实现模式

单例模式的四种实现模式
单例模式实现方式一:
 import settings
 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()
 obj4=MySQL('1.1.1.3',3302)
 print(obj1)
 print(obj2)
 print(obj4)
单例模式实现方式二:
 import settings
 def singleton(cls):
  _instance=cls(settings.IP,settings.PORT)
  def wrapper(*args,**kwargs):
   if args or kwargs:
    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)
 obj1=MySQL() #wrapper()
 obj2=MySQL() #wrapper()
 obj4=MySQL('1.1.1.3',3302)   #wrapper('1.1.1.3',3302)
 print(obj1)
 print(obj2)
 print(obj4)
单例模式实现方式三:
 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 args or kwargs:
    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()
 obj4=MySQL('1.1.1.3',3302)
 print(obj1)
 print(obj2)
 print(obj4)
单例模式实现方式四:
 import settings
 class MySQL:
  def __init__(self, ip, port):
   self.ip = ip
   self.port = port
 instance=MySQL(settings.IP,settings.PORT)
 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()