Describe Python class properties

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• ## __getattr__ is the getattr magic function that is called when the class calls an attribute that does not exist. The value item it passes in is the non-existent value you are calling.

class User(object):
    def __init__(self, name, info):
        self.name = name
        self.info = info
ls = User("李四",{"gender":"male"})print(ls.info)运行结果：{'gender': 'male'}

If you want to get the male attribute, you need to use the

__getattr__ magic method.

class User(object):
    def __init__(self, name, info):
        self.name = name
        self.info = info    def __getattr__(self, item):
        return self.info[item]ls = User("李四",{"gender":"male"})print(ls.gender)运行结果：
male

Attribute descriptor is a powerful general protocol. It is the calling principle of properties, methods, static methods, class methods
• and super().
  
Attribute descriptor is a class that implements a specific protocol. As long as any one of the three methods __get__, __set__ and __delete__ is implemented, this class is a descriptor, which can implement multiple attributes. One way to use the same access logic is to create an instance as a class attribute of another class.
• If an object defines both __get__ and __set__ methods, it is called a data descriptor.
• Objects that only define the __get__ method are called non-data descriptors.
  
Use class methods to create descriptors • Define an IntField class as a descriptor class • Create an instance of the IntField class as an attribute of another User class

class User:
    def __init__(self, age):
        self.age = age    def get_age(self):
        return (str(self.age) + '岁')

    def set_age(self, age):
        if not isinstance(age, int):
            raise TypeError('Type Error')
        self.age = age

tt=User(55)tt.set_age(60)print(tt.get_age())运行结果：60岁

Descriptor Search order • When it is a data descriptor,
• get__ has a higher priority than __dict • When it is a non-data descriptor,
  dict__ has a higher priority than __get

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