[Cython] Bug in NULL handling introduced 0.14.1-1

[Chris Colbert]

I should mention, that these PyObject_Generic* functions are being used from
with __getattribute__, __setattr__, and __delattr__ methods. I should have
added that context in the begining.

On Sun, Feb 13, 2011 at 3:37 PM, Chris Colbert <sccolbert at gmail.com> wrote:

> The problem with delattr (and thus PyObject_DelAttr) arises when you define
> a __delattr__ method on your class. There is not easy way to then call back
> into the "normal" python delattr semantics, except by doing
> object.__delattr__ (which is not optimized by Cython).
>
> Futher, calling PyObject_GenericSetattr(obj, name, NULL) appears to be the
> proper use, given that it properly follows the descriptor chain and will
> call __delete__ if obj.name is a descriptor.
>
> I would argue that there should be at least some way to pass a NULL pointer
> in Cython where a PyObject* is expected.
>
>
> On Sun, Feb 13, 2011 at 3:31 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>wrote:
>
>> Chris Colbert wrote:
>>
>>> I have cython file which is using PyObject_GenericSetAttr
>>> Now in my script I am using that function to generically delete an
>>> attribute by passing a NULL as the last value (this is proper way to trigger
>>> a generic delattr in the Python c-api)
>>>
>>
>> I would have thought the proper way to do that was to use
>> PyObject_DelAttr, which Pyrex exposes as delattr().
>>
>> I don't think PyObject_GenericSetAttr is even meant to be
>> called directly -- it's intended for filling the tp_setattr
>> slot of type objects.
>>
>>
>>  This causes a segfault because the NULL is getting increfed via Py_INCREF
>>> instead of Py_XINCREF.
>>>
>>
>> I would recommend against trying to "fix" this. You got
>> away with it before because you happened to be passing the
>> NULL value directly to a function which is expecting it.
>> But casting NULL to an object reference is not something
>> that should be encouraged, because in any other context it
>> would quickly lead to disaster.
>>
>> --
>> Greg
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/cython-devel/attachments/20110213/706cd750/attachment-0001.html>