覆盖__dir__方法的正确方法是什么？ [英] What is the correct way to override the __dir__ method?

问题描述

这个问题更多地是关于 __ dir __ 而不是 numpy 。

This question is meant to be more about __dir__ than about numpy.

我有一个的子类numpy.recarray （在python 2.7中，numpy 1.6.2），我注意到了 recarray 在 dir 对象时未列出字段名称（因此ipython的自动完成功能不起作用）。

I have a subclass of numpy.recarray (in python 2.7, numpy 1.6.2), and I noticed recarray's field names are not listed when diring the object (and therefore ipython's autocomplete doesn't work).

尝试修复它，我尝试在我的子类中覆盖 __ dir __ ，如下所示：

Trying to fix it, I tried overriding __dir__ in my subclass, like this:

def __dir__(self):
    return sorted(set(
               super(MyRecArray, self).__dir__() + \
               self.__dict__.keys() + self.dtype.fields.keys()))

结果为： AttributeError：'super'对象没有属性'__dir __'。
（我发现这里这应该在python 3.3中实际工作......）

which resulted with: AttributeError: 'super' object has no attribute '__dir__'. (I found here this should actually work in python 3.3...)

作为解决方法，我试过：

As a workaround, I tried:

def __dir__(self):
    return sorted(set(
                dir(type(self)) + \
                self.__dict__.keys() + self.dtype.fields.keys()))

据我所知，这个有效，但当然不是很优雅。

As far as I can tell, this one works, but of course, not as elegantly.

问题：

1. 后一种解决方案在我的情况下是正确的，即对于 recarray ？


2. 有没有办法让它在一般情况下有效？在我看来它不适用于多重继承（打破超级 - 调用链），当然，对于没有 __ dict __ <的对象/ code> ...


3. 您知道为什么 recarray 不支持列出其字段名称开头吗？仅仅是疏忽？

1. Is the latter solution correct in my case, i.e. for a subclass of recarray?
2. Is there a way to make it work in the general case? It seems to me it wouldn't work with multiple inheritance (breaking the super-call chain), and of course, for objects with no __dict__...
3. Do you know why recarray does not support listing its field names to begin with? mere oversight?

推荐答案

Python 2.7 +，3.3 + class mixin，简化了方法。希望它会有所帮助。 要点。

Python 2.7+, 3.3+ class mixin that simplifies implementation of __dir__ method in subclasses. Hope it will help. Gist.

import six
class DirMixIn:
    """ Mix-in to make implementing __dir__ method in subclasses simpler
    """

    def __dir__(self):
        if six.PY3:
            return super(DirMixIn, self).__dir__()
        else:
            # code is based on
            # http://www.quora.com/How-dir-is-implemented-Is-there-any-PEP-related-to-that
            def get_attrs(obj):
                import types
                if not hasattr(obj, '__dict__'):
                    return []  # slots only
                if not isinstance(obj.__dict__, (dict, types.DictProxyType)):
                    raise TypeError("%s.__dict__ is not a dictionary"
                                    "" % obj.__name__)
                return obj.__dict__.keys()

            def dir2(obj):
                attrs = set()
                if not hasattr(obj, '__bases__'):
                    # obj is an instance
                    if not hasattr(obj, '__class__'):
                        # slots
                        return sorted(get_attrs(obj))
                    klass = obj.__class__
                    attrs.update(get_attrs(klass))
                else:
                    # obj is a class
                    klass = obj

                for cls in klass.__bases__:
                    attrs.update(get_attrs(cls))
                    attrs.update(dir2(cls))
                attrs.update(get_attrs(obj))
                return list(attrs)

            return dir2(self)

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