Python进阶-----描述符(__get__(),__set__(),__delete__())

1 class Foo: #在python3中Foo是新式类,它实现了三种方法,这个类就被称作一个描述符
2     def __get__(self, instance, owner):
3         print(‘__get__(),被执行了‘)
4     def __set__(self, instance, value):
5         print(‘__set__(),被执行了‘)
6     def __delete__(self, instance):
7         print(‘__delete__(),被执行了‘)

1 class Test:
2     x = Foo()
3     def __init__(self,x):
4         self.x = x
5 
6 t = Test(2)      #‘__set__(),被执行了‘
7 print(t.x)         #‘__get__(),被执行了‘   ‘None‘

 1 #数据描述符
 2 class Foo:
 3     def __set__(self, instance, value):
 4         print(‘set‘)
 5     def __get__(self, instance, owner):
 6         print(‘get‘)
 7 
 8 #非数据描述符
 9 class Foo:
10     def __get__(self, instance, owner):
11         print(‘get‘)