Nova's test suite fails with python 2.7.2rc1

I've not had time to whip up anything coherent to file a bug report upstream. If someone else wants to, please feel free to do so.

Reported upstream as:

http://code.google.com/p/pymox/issues/detail?id=35

It's almost certainly related to this entry in Misc/NEWS:

- Correct lookup of __dir__ on objects. Among other things, this causes errors
  besides AttributeError found on lookup to be propagated.

and this log entry:

changeset: 70312:b2fc6b9f850f
branch: 2.7
parent: 70304:9d004a9a2ced
user: Benjamin Peterson <email address hidden>
date: Mon May 23 16:11:05 2011 -0500
files: Lib/test/test_descr.py Misc/NEWS Objects/object.c
description:
correctly lookup __dir__

As there's no issue number to link this to the Python tracker, I need to as Benjamin why this change was made and whether it's really appropriate for an rc, let alone a patch release.

This reproduces the problem:

=== mymodule.py ===

class MyClass(object):
    pass

=== reproduce.py ===

import mox
import mymodule

class Test(object):
    def __init__(self):
        self.mox = mox.Mox()
        self.mox.StubOutWithMock(mymodule, 'MyClass', use_mock_anything=True)
        self.mox.CreateMock(mymodule.MyClass)

Test()

I don't know if this is CPython changing its behaviour to be closer to spec and pymox depending on CPython implementation details. I'm hoping someone else can clear this up.

I think this one is even simpler to illustrate the change:

class Foo:
    def __dir__(self):
        return ['a', 'b', 'c']

class Bar:
    def __dir__(self):
        return ('a', 'b', 'c')

print dir(Foo())
print dir(Bar())

AFAICT, in Python 2.7.1 you get two lines of ['a', 'b', 'c'] while in 2.7.2rc2, the second line gives you the TypeError.

http://bugs.python.org/issue12248

This is what you actually get on 2.7.1:

$ python
Python 2.7.1 (r271:86832, Mar 24 2011, 22:44:47)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class Foo:
... def __dir__(self):
... return ['a', 'b', 'c']
...
>>> class Bar:
... def __dir__(self):
... return ('a', 'b', 'c')
...
>>> print dir(Foo())
['__dir__', '__doc__', '__module__']
>>> print dir(Bar())
['__dir__', '__doc__', '__module__']

So __dir__ was actually completely broken on old-style classes in 2.7.1. You're only seeing the behavior it would have had if __dir__ worked.

This bug was fixed in the package python-mox - 0.5.3-1ubuntu2

---------------
python-mox (0.5.3-1ubuntu2) oneiric; urgency=low

  * python-2.7.2-compat.patch: Python 2.7.2 calls __dir__ for old-style
    classes. Make sure a MockAnything returns a list of some sort
    instead of a MockMethod (LP: #791221)
 -- Soren Hansen <email address hidden> Mon, 06 Jun 2011 10:36:48 +0200

Anything left to do on Nova upstream or ubuntu/nova packaging ?

Thierry: No

BTW, reverting/working around the change was rejected for 2.7.2 so upstream will need to adjust.