Python learns the attributes of such and instances; adorner @property

1. Everything is an object, whether it is a class or an instance.
   
2. Python is a strong dynamic language, and Java differs in this regard.

class Ab():    a = 666# 定义类对象Ab，自带属性a，值为666# 使用Ab.__dict__可以查看类Ab的属性us1 = Ab()us2 = Ab()# 定义两个实例对象us1、us2，这两个实例自身并不具备任何属性# 只有在__init__中定义了self.arg=xxx的情况下，实例默认会具备arg属性

1. In a dynamic language, a property comes with an action method: Get (Read), set (write), or define a delete

print(Ab.a, us1.a, us2.a)# 获取属性a，输出均为666# 属性查找机制：自下而上。# python查找对象us1不具备属性a，就会在其所属的类对象Ab中查找属性a。us1.a += 333# 输出999# 首先查找us1.a未找到，于是使用Ab.a# 然后设置Ab.a+333的值为us1.a属性的值Ab.a += 222# 输出888print(Ab.a, us1.a, us2.a)# 输出分别为888，999, 888# us1已具备属性a，值为999.所以不再类中查找# us2不具备属性a，所以使用类Ab.a的值

@property

Change the method of a class to a property

1. Reason:

   The property can be read and written without using the method restriction attribute;
   Using methods to restrict read and write, it is cumbersome to read and write (to invoke three methods: Get, set, Del)

2. Workaround: Decorator Property

   Converts a method to a property, which is convenient to call and prevents arbitrary changes.

3. Example

class Student(object):    @property    def score(self):    ‘‘‘    原本定义为get_score()    调用方法：xiaopang.get_score()    如今调用属性score：xiaopang.score    ‘‘‘        return self._score        @score.setter    def score(self, value):    ‘‘‘    原本定义为set_score()    调用方法：xiaopang.set_score(80)    如今调用属性score：xiaopang.score = 80    ‘‘‘        if not isinstance(value, int):            raise ValueError(‘score must be an integer!‘)        if value < 0 or value > 100:            raise ValueError(‘score must between 0 ~ 100!‘)        self._score = value

1. Property principle

• The property is not directly exposed, but it is passed by the getter and setter method.
• Dir (property) See also Deleter method, if only getter (default), no setter, the attribute is read-only

Python learns the attributes of such and instances; adorner @property