python - What is the correct way to override the __dir__ method?

Question

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

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).

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()))

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

As a workaround, I tried:

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

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

Questions:

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?

Answer 1

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)