python对象 属性访问优先级：object.name
python对象 属性访问优先级：object.name
object.__getattribute__(self, name)- 类 中的 数据描述符
object.__dict__.get(name)自身属性字典object.__class__.__dict__.get(name)类属性字典 / 非数据描述符object.__getattr__(name)
- 描述符：定义了
__get__()的 类 #没有定义，返回描述符（普通类）实例 - 数据（覆盖型）描述符: 定义了
__set__()或者__delete__()中一个以上
类属性name如果是数据描述符，会截断 实例的属性访问和修改:
"self.name = value"；就变成了name.__set__(self, ins, value)
"self.name"；就变成了name.__get__(self, ins, ins.__class__ )
-
定义
__delete__()没定义__set__()，在实例赋值时就会报错 -
定义
__set__()没定义__delete__()，在实例删除 就会报错
试验代码：
# -*- coding: utf-8 -*-
# author: willowj
# date: 2018-01-03 21:32:50
# py2.7
class Descdata(object):
def __init__(self, name=''):
self.name = name
self.value = 0
# 常用dict，可根据不同的instance set不同的值,get 返回不同的值
# 相当于给每一个实例绑定了一个值
def __get__(self, instance, owner=None):
print("Descdata:inst> %s__get__() is called---" % self.name,
instance, owner)
return self.value
def __set__(self, instance, value):
print("Descdata:inst> %s __set__() is called---" % self.name,
instance, value)
self.value = value
def __delete__(self):
print('Descdata inst %s: .__delete__---'% self.name)
del self
class Desc_not_data(object):
def __init__(self, name='', value='as654'):
self.name = name
self.value = value
def __get__(self, instance, owner=None):
print("Desc_not_data:inst> %s__get__() is called---" % self.name,
instance, owner)
return self.value
class Base(object):
def __getattribute__(self, *args, **kwargs):
print("Base __getattribute__() is called")
return object.__getattribute__(self, *args, **kwargs)
class Test(Base):
a = 'abc'
d_d = Descdata(name='d_d') # 数据描述符,如果实例有同名属性 会拦截
nd = Desc_not_data(name='nd') # 非数据描述符,如果实例有同名属性 不会拦截
nd2 = Desc_not_data(name='nd2') # 非数据描述符,如果实例有同名属性 不会拦截
def __init__(self, *args, **kwargs):
self.d_d = 'Test_ins self d_d'
# if cls.d_d 是数据描述符,这里就是调用数据描述符的 __set__
# 类属性name如果是数据描述符,会截断--实例ins: "self.name = value"；
# 要是定义了 __delete__ 没定义 __set__，在实例赋值时就会报错
self.nd2 = 'Test_>nd2' # 优先于 非数据描述符
def __getattribute__(self, *args, **kwargs):
print("Test __getattribute__() is called")
return Base.__getattribute__(self, *args, **kwargs)
def __getattr__(self, name):
print("Test __getattr__() is called ")
return name + " from __getattr__"
q = Test() # __init__ : 赋值 数据描述符
# ('Descdata:inst> d_d __set__() is called---', <__main__.Test object at 0x0000000002B69DD8>, 'Test_ins self d_d')
print('-'*30,u'visit data descriptor')
print 'q.d_d\n', q.d_d, '\n'
# ('------------------------------', u'visit data descriptor')
# q.d_d
# Test __getattribute__() is called
# Base __getattribute__() is called
# ('Descdata:inst> d_d__get__() is called---', <__main__.Test object at 0x0000000002B69DD8>, <class '__main__.Test'>)
# Test_ins self d_d
print('-'*30,u'visit non data descriptor not overided by instance')
print 'q.nd\n', q.nd, '\n'
# ('------------------------------', u'visit non data descriptor')
# q.nd
# Test __getattribute__() is called
# Base __getattribute__() is called
# ('Desc_not_data:inst> nd__get__() is called---', <__main__.Test object at 0x0000000002B69DD8>, <class '__main__.Test'>)
# as654
print('-'*30,u'visit non data descriptor overided by instance')
print 'q.nd2\n', q.nd2, '\n'
# ('------------------------------', u'visit non data descriptor overided by instance')
# q.nd2
# Test __getattribute__() is called
# Base __getattribute__() is called
# Test_>nd2
print('-'*30,u"visit attr that not exist" )
print 'q.nnnnnnnnnnnnn\n', q.nnnnnnnnnnnnn, '\n'
# ('------------------------------', u'visit attr that not exist')
# q.nnnnnnnnnnnnn
# Test __getattribute__() is called
# Base __getattribute__() is called
# Test __getattr__() is called
# nnnnnnnnnnnnn from __getattr__
print('\n q.__dict__')
print q.__dict__
# q.__dict__
# Test __getattribute__() is called
# Base __getattribute__() is called
# {'nd2': 'Test_>nd2'}
print('-'*30,'\n',' Test.__dict__')
a_dict_ = dict(Test.__dict__)
for k in a_dict_:
print k,' '*(20-len(k)),a_dict_[k]
# ('------------------------------', '\n', ' Test.__dict__')
# a abc
# __module__ __main__
# nd <__main__.Desc_not_data object at 0x0000000002AA9DA0>
# __getattribute__ <function __getattribute__ at 0x0000000002AF0048>
# __getattr__ <function __getattr__ at 0x0000000002AF00B8>
# d_d <__main__.Descdata object at 0x0000000002AA9D30>
# nd2 <__main__.Desc_not_data object at 0x0000000002AA9DD8>
# __doc__ None
# __init__ <function __init__ at 0x0000000002AB7F98>
print('-'*30)
print Test.__dict__['__getattribute__'] ,type(Test.__dict__['__getattribute__'])
# <function __getattribute__ at 0x0000000002B74048> <type 'function'>
推荐资料
https://www.cnblogs.com/Jimmy1988/p/6808237.html
https://www.zhihu.com/question/25391709/answer/30634637
