描述符

class Type:
    def __init__(self,key):
        self.key = key

    def __get__(self, instance, owner):
        print('执行get方法')
        return instance.__dict__[self.key]

    def __set__(self, instance, value):
        print('执行set方法')
        instance.__dict__[self.key] = value

    def __delete__(self, instance):
        instance.__dict__.pop(self.key)
class Foo:
    name = Type('name')

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


f1 = Foo('alex')
f1.name = 2
print(f1.__dict__)
print(f1.name)
输出：
执行set方法
执行set方法
{'name': 2}
执行get方法
2

可以对赋值加上条件判断

class Type:
    def __init__(self,key):
        self.key = key

    def __get__(self, instance, owner):
        print('执行get方法')
        return instance.__dict__[self.key]

    def __set__(self, instance, value):
        print('执行set方法')
        if not isinstance(value,str):
            # print('你传入得不是字符串')
            raise TypeError('你传入的不是字符串')
        instance.__dict__[self.key] = value

    def __delete__(self, instance):
        instance.__dict__.pop(self.key)
class Foo:
    name = Type('name')

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


f1 = Foo(3)
# f1.name = 2
# print(f1.__dict__)
# print(f1.name)
输出：
执行set方法
Traceback (most recent call last):
  File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 25, in <module>
    f1 = Foo(3)
  File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 22, in __init__
    self.name = name
  File "C:/Users/Administrator/Desktop/python/3月12日/描述符应用.py", line 13, in __set__
    raise TypeError('你传入的不是字符串')
TypeError: 你传入的不是字符串