面向对象-描述符

Posted 2021-01-14 chrrydot

描述符使用

Foo接管了Bar的x值，当x值被操作的时候都调用Foo相应的get/set/delete操作

class Foo:
    def __get__(self,instance,owner):
        print(‘===>get‘,instance,owner)
    def __set__(self,instance,value):
        print(‘===>set‘,instance,value)
    def __delete__(self, instance):
        print(‘===>delete‘,instance)

class Bar:
    x = Foo()
    def __init__(self,n):
        self.x = n

b1 = Bar(10)
print(b1.__dict__)
print(Bar.__dict__)
print(b1.x)
‘‘‘
===>set <__main__.Bar object at 0x0000022A4A214D68> 10
{}
{‘__module__‘: ‘__main__‘, ‘x‘: <__main__.Foo object at 0x0000022A4A214C50>, ‘__init__‘: <function Bar.__init__ at 0x0000022A4A1F6C80>, ‘__dict__‘: <attribute ‘__dict__‘ of ‘Bar‘ objects>, ‘__weakref__‘: <attribute ‘__weakref__‘ of ‘Bar‘ objects>, ‘__doc__‘: None}
===>get <__main__.Bar object at 0x0000022A4A214D68> <class ‘__main__.Bar‘>
None
‘‘‘

class Foo:
    def __get__(self,instance,owner):
        print(‘===>get‘,instance,owner)
    def __set__(self,instance,value):
        print(‘===>set‘,instance,value)
    def __delete__(self, instance):
        print(‘===>delete‘,instance)

class Bar:
    x = Foo()
    def __init__(self,n):
        self.x = n

# print(Bar.x)
# Bar.x = 1 #不触发描述符，因为类属性优先级更高,如果不注释，后面的语句也不触发描述符
b1 = Bar(10)
print(b1.x)
del b1.x
‘‘‘
===>set <__main__.Bar object at 0x000001D368C14CF8> 10
===>get <__main__.Bar object at 0x000001D368C14CF8> <class ‘__main__.Bar‘>
None
===>delete <__main__.Bar object at 0x000001D368C14CF8>
‘‘‘

描述符优先级

1. 类属性
2. 数据描述符
3. 实例属性
4. 非数据描述符
5. 找不到的属性触发__getattr__()

class Foo:
    def __get__(self,instance,owner):
        print(‘===>get‘,instance,owner)
    def __set__(self,instance,value):
        print(‘===>set‘,instance,value)
    def __delete__(self, instance):
        print(‘===>delete‘,instance)

class Bar:
    x = Foo()
    def __init__(self,n):
        self.x = n

# print(Bar.x)
Bar.x = 1 #不触发描述符，因为类属性优先级更高
‘‘‘

Process finished with exit code 0
‘‘‘