疫情环境下的网络学习笔记 python 4.15 作业

4.15作业

1. 在元类中控制把自定义类的数据属性都变成大写

   class Mymeta(type):
       def __new__(cls, name,bases,attrs):
           for attr,val in attrs.items():
               if not attr.startswith('_'):
                   attrs.pop(attr)
                   attr = attr.upper()
                   attrs[attr] = val
           print(attrs)
           return type.__new__(cls, name,bases,attrs)
   
   
   class Upper(object, metaclass=Mymeta):
       name = 'Thresh'
       motto = 'what delighted agony we shall inflict?'
   

2. 在元类中控制自定义的类无需__init__方法

   1.元类帮其完成创建对象，以及初始化操作；

   2.要求实例化时传参必须为关键字形式，否则抛出异常TypeError: must use keyword argument

   3.key作为用户自定义类产生对象的属性，且所有属性变成大写

   class Mymeta(type):
       def __call__(self, *args, **kwargs):
           if args:
               raise TypeError('必须是关键字参数')
           obj = self.__new__(self)
           for k,v in kwargs.items():
               if not k.startswith('_'):
                   obj.__dict__[k.upper()]=v
           return obj
   
   
   class Upper(object, metaclass=Mymeta):
       name = 'Thresh'
       motto = 'what delighted agony we shall inflict?'
   
   obj = Upper(age=18)
   print(obj.__dict__)
   

3. 在元类中控制自定义的类产生的对象相关的属性全部为隐藏属性

   class Mymeta(type):
       def __init__(self,class_name,class_bases,class_dic):
           super(Mymeta,self).__init__(class_name,class_bases,class_dic)
   
       def __call__(self, *args, **kwargs):
           obj = self.__new__(self)
           self.__init__(obj, *args, **kwargs)
           obj.__dict__={'_%s__%s' %(self.__name__,k):v for k,v in obj.__dict__.items()}
           print(obj.__dict__)
           return obj
   
   class Upper(object, metaclass=Mymeta):
       def __init__(self,name,age):
           self.name = name
           self.age = age
   
   obj = Upper('deimos',21)
   

4. 基于元类实现单例模式

   需求：实例化多次，指向同一个内存地址

   #settings.py文件内容如下
   HOST='1.1.1.1'
   PORT=3306
   

   # 看不太懂 先把答案搬上来
   import settings
   class Mymeta(type):
       def __init__(self,name,bases,dic):
           self.__instance = object.__new__(self)  # 产生instance对象
           self.__init__(self.__instance, settings.HOST, settings.PORT)  # 初始化instance
           # 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):
           if args or kwargs:
               obj=object.__new__(self)
               self.__init__(obj,*args,**kwargs)
               return obj
           return self.__instance
   
   class Mysql(metaclass=Mymeta):
       def __init__(self,host,port):
           self.host=host
           self.port=port
   
   obj1=Mysql()
   obj2=Mysql()
   obj3=Mysql()
   print(obj1 is obj2 is obj3)