autoclass and instance attributes

Question

According to the sphinx documentation, the .. autoattribute directive should be able to document instance attributes. However, if I do::

.. currentmodule:: xml.etree.ElementTree

.. autoclass:: ElementTree

   .. autoattribute:: ElementTree._root

Then when building I get an AttributeError:

Traceback (most recent call last):etree.ElementTree.ElementTree                 
  File "/Volumes/Raptor/Library/Python/2.7/lib/python/site-packages/sphinx/ext/autodoc.py", line 326, in import_object
    obj = self.get_attr(obj, part)
  File "/Volumes/Raptor/Library/Python/2.7/lib/python/site-packages/sphinx/ext/autodoc.py", line 232, in get_attr
    return safe_getattr(obj, name, *defargs)
  File "/Volumes/Raptor/Library/Python/2.7/lib/python/site-packages/sphinx/util/inspect.py", line 70, in safe_getattr
    raise AttributeError(name)
AttributeError: _root

even though if I instantiate ElementTree and try and access the _root attribute, it works fine::

>>> from xml.etree.ElementTree import ElementTree
>>> e = ElementTree()
>>> hasattr(e, '_root')
True

What am I doing wrong?

(I'm actually having this issue with one of my own classes, but am just using the ElementTree class as an example since it's in the standard library)

Answer 1

This looks like a bug in the way non-public instance attributes are handled. Sphinx is supposed to be able to recognize instance attributes defined in __init__.

I can't say how this should be fixed. There is an open bug report that seems to be related: Non-public instance attributes are not documented without __slots__.

If the following line is added to the definition of the ElementTree class in ElementTree.py,

__slots__  = ["_root"]

then the AttributeError that you get goes away.