[英]Inspecting data descriptor attributes in python
I'm attempting to use a data descriptor to provide some custom get/set functionality to attributes of a class. 我正在尝试使用数据描述符为类的属性提供一些自定义的get / set功能。 I'd like to be able to inspect the class at runtime and get a list of data descriptors on that class, and maybe even determine what the type of the descriptor is.
我希望能够在运行时检查类并获取该类的数据描述符列表,甚至可以确定描述符的类型。
The problem is that when I look at the members I get using inspect.getmembers
my data descriptor attributes are resolved (their __get__
method is already called and that result is set as the value of the object). 问题是,当我查看使用
inspect.getmembers
的成员时,我的数据描述符属性被解析(它们的__get__
方法已被调用,结果被设置为对象的值)。
I'm using the example from: http://docs.python.org/2/howto/descriptor.html 我正在使用以下示例: http : //docs.python.org/2/howto/descriptor.html
import inspect
class RevealAccess(object):
"""A data descriptor that sets and returns values
normally and prints a message logging their access.
"""
def __init__(self, initval=None, name='var'):
self.val = initval
self.name = name
def __get__(self, obj, objtype):
print 'Retrieving', self.name
return self.val
def __set__(self, obj, val):
print 'Updating', self.name
self.val = val
class MyClass(object):
x = RevealAccess(10, 'var "x"')
y = 5
if __name__ == '__main__':
for x in inspect.getmembers(MyClass, inspect.isdatadescriptor):
print x
When I run this, I get: 当我运行这个时,我得到:
Retrieving var "x"
('__weakref__', <attribute '__weakref__' of 'MyClass' objects>)
What I expect is more like: 我的期望更像是:
('x', <attribute 'x' of 'MyClass' objects>)
('__weakref__', <attribute '__weakref__' of 'MyClass' objects>)
I know I'm missing something I just can't put my finger on it. 我知道我错过了一些我不能把手指放在上面的东西。 Any help appreciated.
任何帮助赞赏。
To get the descriptor itself, you can look into class __dict__
: 要获取描述符本身,您可以查看类
__dict__
:
MyClass.__dict__['x']
But the better way is to modify the getter: 但更好的方法是修改getter:
def __get__(self, obj, objtype):
print 'Retrieving', self.name
if obj is None: # accessed as class attribute
return self # return the descriptor itself
else: # accessed as instance attribute
return self.val # return a value
Which gives: 这使:
Retrieving var "x"
('__weakref__', <attribute '__weakref__' of 'MyClass' objects>)
('x', <__main__.RevealAccess object at 0x7f32ef989890>)
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