使用getattr获取祖父母类的属性 [英] Getting an attribute of grandparent class using getattr

问题描述

我试图从ClassB的实例访问Base类的实例属性(inst_baseA / inst_baseB)，具体取决于实例(对象ClassB的self.x)的属性.

I'm trying to access an instance attribute (inst_baseA / inst_baseB) of Base class from an instance of ClassB, depending on an attribute of the instance (self.x of object ClassB).

这是我的代码:

class Base(object):
    def __init__(self):
        self.inst_baseA = 'base_B'
        self.inst_baseB = 'base_A'


class ClassA(object):
    def __init__(self):
        self.node = Base()


class ClassB(ClassA):
    def __init__(self):
        super(ClassB, self).__init__()
        self.x = 'base_A'

这是我首先尝试的:

>>> b = ClassB()
>>> getattr(b, 'node.inst_{}'.format(b.x))

Traceback (most recent call last):
  File "<pyshell#26>", line 1, in <module>
    getattr(b, 'node.inst_{}'.format(b.x))
AttributeError: 'ClassB' object has no attribute 'node.inst_base_A'

如果我将调用链接到getattr，我将克服这个问题:

I overcome this if I chain calls to getattr:

>>> getattr(getattr(b, 'node'), b.x)
'base_A'

出于好奇:除了对getattr进行两次调用之外，是否有其他方法可以从孙辈类中获取Base类的属性?

Out of curiosity: Is there a way to get an attribute of the Base class from grandchildren class besides doing two calls to getattr?

更新:我需要它的原因是我正在尝试: -从祖父母类获取属性(inst_baseA或inst_baseB) -取决于实例的属性(x的值)

Update: the reason I need it is I'm trying to: - Get an attribute fron grandparent class (either inst_baseA or inst_baseB) - Depending on an attribute on my instance (the value of x)

所以我的代码实际上是这样的:getattr(self, 'node.{}'.format(self.x)).第一次我没有正确地解释它，希望现在更有意义.

So my code is actually something like: getattr(self, 'node.{}'.format(self.x)). I didn't explain it correctly at the first time, hope it makes more sense now.

推荐答案

有

There's operator.attrgetter, but it's really not meant for this kind of thing, so the syntax is pretty awkward:

>>> operator.attrgetter('node.inst_base')(b)
'base'

但这确实是很不直观的，因此，为了避免使阅读您的代码的人感到困惑，最好改用自己的多getattr:

But this is really quite unintuitive, so to avoid confusing people who read your code, it's probably better to roll your own multi-getattr instead:

def get_multi_attr(obj, attrs):
    for attr in attrs.split('.'):
        obj = getattr(obj, attr)
    return obj

>>> get_multi_attr(b, 'node.inst_base')
'base'

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