On 2/20/23 20:08, Nir Soffer wrote:
> On Mon, Feb 20, 2023 at 10:45 AM Laszlo Ersek <ler...@redhat.com> wrote:
>>
>> On 2/17/23 17:52, Eric Blake wrote:
>>> On Thu, Feb 16, 2023 at 03:09:02PM +0100, Laszlo Ersek wrote:
>>
>>>> - Py_BuildValue with the "O" format specifier transfers the new list's
>>>> *sole* reference (= ownership) to the just-built higher-level object "args"
>>>
>>> Reference transfer is done with "N", not "O". That would be an
>>> alternative to decreasing the refcount of py_array on success, but not
>>> eliminate the need to decrease the refcount on Py_BuildValue failure.
>>>
>>>>
>>>> - when "args" is killed (decref'd), it takes care of "py_array".
>>>>
>>>> Consequently, if Py_BuildValue fails, "py_array" continues owning the
>>>> new list -- and I believe that, if we take the new error branch, we leak
>>>> the object pointed-to by "py_array". Is that the case?
>>>
>>> Not quite. "O" is different than "N".
>>
>> I agree with you *now*, looking up the "O" specification at
>> <https://docs.python.org/3/c-api/arg.html#building-values>.
>>
>> However, when I was writing my email, I looked up Py_BuildValue at that
>> time as well, just elsewhere. I don't know where. Really. And then that
>> documentation said that the reference count would *not* be increased. I
>> distinctly remember that, because it surprised me -- I actually recalled
>> an *even earlier* experience reading the documentation, which had again
>> stated that "O" would increase the reference count.
>
> Maybe here:
> https://docs.python.org/2/c-api/arg.html#building-values
>
> Looks like another incompatibility between python 2 and 3.
Yes, thank you! That's it *exactly*!
O (object) [PyObject *]
Store a Python object (without any conversion) in a C object
pointer. The C program thus receives the actual object that was
passed. The object’s reference count is not increased. The pointer
stored is not NULL.
Laszlo
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