单例模式实现的多种方式

class C1:
__instance = None

def __init__(self, name, age):
    self.name = name
    self.age = age

@classmethod
def singleton(cls):
    if not cls.__instance:
        cls.__instance = cls('jason', 18)
    return cls.__instance


obj1 = C1.singleton()
obj2 = C1.singleton()
obj3 = C1.singleton()
print(id(obj1), id(obj2), id(obj3))
obj4 = C1('kevin', 28)
obj5 = C1('tony', 38)
print(id(obj4), id(obj5))



class Mymeta(type):
    def __init__(self, name, bases, dic):  # 定义类Mysql时就触发
        # 事先先从配置文件中取配置来造一个Mysql的实例出来
        self.__instance = object.__new__(self)  # 产生对象
        self.__init__(self.__instance, 'jason', 18)  # 初始化对象
        # 上述两步可以合成下面一步
        # self.__instance=super().__call__(*args,**kwargs)
        super().__init__(name, bases, dic)

def __call__(self, *args, **kwargs):  # Mysql(...)时触发
    if args or kwargs:  # args或kwargs内有值
        obj = object.__new__(self)
        self.__init__(obj, *args, **kwargs)
        return obj
    return self.__instance


class Mysql(metaclass=Mymeta):
    def __init__(self, name, age):
        self.name = name
        self.age = age

obj1 = Mysql()
obj2 = Mysql()
print(id(obj1), id(obj2))
obj3 = Mysql('tony', 321)
obj4 = Mysql('kevin', 222)
print(id(obj3), id(obj4))

基于模块的单例模式:提前产生一个对象之后导模块使用

  class C1:
      def __init__(self, name):
          self.name = name

  obj = C1('jason')


  def outer(cls):
      _instance = cls('jason', 18)
      def inner(*args, **kwargs):
          if args or kwargs:
              obj = cls(*args, **kwargs)
              return obj
          return _instance

      return inner


  @outer  # Mysql=outer(Mysql)
  class Mysql:
      def __init__(self, host, port):
          self.host = host
          self.port = port


  obj1 = Mysql()
  obj2 = Mysql()
  obj3 = Mysql()
  print(obj1 is obj2 is obj3)  # True

  obj4 = Mysql('1.1.1.3', 3307)
  obj5 = Mysql('1.1.1.4', 3308)
  print(obj3 is obj4)  # False

pickle序列化模块

优势：能够序列化python中所有的类型
缺陷：只能够在python中使用无法跨语言传输

需求：产生一个对象并保存到文件中取出来还是一个对象

   class C1:
      def __init__(self, name, age):
          self.name = name
          self.age = age

      def func1(self):
          print('from func1')

      def func2(self):
          print('from func2')

  obj = C1('jason', 18)

   import json
   ith open(r'a.txt','w',encoding='utf8') as f:
       json.dump(obj, f)
   import pickle
   with open(r'a.txt', 'wb') as f:
       pickle.dump(obj, f)
   with open(r'a.txt','rb') as f:
       data = pickle.load(f)
   print(data)
   data.func1()
   data.func2()
   print(data.name)

python基础知识

单例模式实现的多种方式

pickle序列化模块