描述符

class Foo:
    def __set__(selfsself,instance, value):
        print("set")
    def __get__(self, instance, owner):
        print("get")
        

class Foo:

    def __get__(self, instance, owner):
        print("get")

class Foo:
    def __get__(self, instance, owner):   #这里的instance是实例对象b1,owner是类Bar
        print("===>get方法")
        return instance.__dict__[‘x‘]
    def __set__(self, instance, value):  #这里的instance是实例对象b1，value是传入的值
        print("===>set方法")
        instance.__dict__[‘x‘] = value
    def __delete__(self, instance):
        print("===>delete方法")
        instance.__dict__.pop(‘x‘)

class Bar:
    x = Foo()   #将x 全权给Foo类代理,此时 x 就是描述符
    def __init__(self, n):
        self.x = n

b1 = Bar(10)
print(b1.__dict__)
print(b1.x)
del b1.x
print(b1.__dict__)
b1.x = 222222222
print(b1.__dict__)
b1.y = 2222
print(b1.__dict__)

class Foo:
    def __get__(self, instance, owner):   #这里的instance是实例对象b1,owner是类Bar
        print("===>get方法")
        # return instance.__dict__[‘x‘]
    def __set__(self, instance, value):  #这里的instance是实例对象b1，value是传入的值
        print("===>set方法")
        # instance.__dict__[‘x‘] = value
    def __delete__(self, instance):
        print("===>delete方法")
        # instance.__dict__.pop(‘x‘)
class Bar:
    x = Foo()
    def __init__(self, n):
        self.x = n

b1 = Bar(10)
print(Bar.__dict__)  #这里打印字典看出：x 是一个对象
Bar.x = 10
print(Bar.x)
print(Bar.__dict__)  #当Bar.x为x后，直接覆盖了描述符的操作

class Foo:
    def __get__(self, instance, owner):   #这里的instance是实例对象b1,owner是类Bar
        print("===>get方法")
        # return instance.__dict__[‘x‘]
    def __set__(self, instance, value):  #这里的instance是实例对象b1，value是传入的值
        print("===>set方法")
        # instance.__dict__[‘x‘] = value
    def __delete__(self, instance):
        print("===>delete方法")
        # instance.__dict__.pop(‘x‘)
class Bar:
    x = Foo()
    def __init__(self, n):
        self.x = n

b1 = Bar(10)
b1.x = 10  #可以看出。用实例为变量赋值时，直接触发数据描述符
print(b1.__dict__)

class Foo:
    def __get__(self, instance, owner):   #这里的instance是实例对象b1,owner是类Bar
        print("===>get方法")
        # return instance.__dict__[‘x‘]
    # def __set__(self, instance, value):  #这里的instance是实例对象b1，value是传入的值
    #     print("===>set方法")
    #     # instance.__dict__[‘x‘] = value
    # def __delete__(self, instance):
        print("===>delete方法")
        # instance.__dict__.pop(‘x‘)
class Bar:
    x = Foo()
    def __init__(self, n):
        self.x = n

b1 = Bar(10)
b1.x = 10  #可以看出。用实例为变量赋值时，没有触发非数据描述符
print(b1.__dict__)

class Foo:
    def __get__(self, instance, owner):   #这里的instance是实例对象b1,owner是类Bar
        print("===>get方法")
        # return instance.__dict__[‘x‘]
    # def __set__(self, instance, value):  #这里的instance是实例对象b1，value是传入的值
    #     print("===>set方法")
    #     # instance.__dict__[‘x‘] = value
    # def __delete__(self, instance):
        print("===>delete方法")
        # instance.__dict__.pop(‘x‘)
class Bar:
    x = Foo()
    def __init__(self, n):
        self.x = n
    def __getattr__(self, item):
        print("qaq")

b1 = Bar(10)
b1.yyyy   #当查找的属性不存在时