Undocumented Python 2.6 change: Py_None vs NULL when C implementation raises exception

[Heikki Toivonen]

Martin v. Löwis wrote:
> Heikki Toivonen wrote:
>> I tracked this down to the C code incorrectly returning Py_None when it
>> should have returned NULL. Changing the C code to return NULL made it
>> behave correctly in 2.6.
> 
> Can you please be specific what function you are talking about?

Perhaps it wasn't clear that I was referring to the C code in an
extension, M2Crypto. I assumed that this affected all extension code
like this, which is why I didn't mention the actual lines. It appears
from Fredrik's comment that this might not be just a 2.6 issue, but that
this problem has cropped up in the past as well more or less randomly.

>> I don't know how common a mistake it is to return Py_None when NULL
>> should have been returned, but it might be worth a note in the list of
>> changes for 2.6 that this behavior changed, don't you think?
> 
> Perhaps. OTOH, perhaps the change is completely erroneous. In that case,
> rather than documenting it, it should be reverted.
> 
> Unfortunately, as you keep the specific issue secret, none of this will
> happen, as we have no clue what you are talking about.

I don't know what change in Python caused the change in M2Crypto
behavior. I can only point you to the change I made in M2Crypto if you
are interested:
http://viewcvs.osafoundation.org/m2crypto/trunk/SWIG/_pkcs7.i?rev=531&r1=611&r2=531

If you revert that change and run the M2Crypto unit tests you will see
the single error in the tests.

> I'm sure there are tons of silent changes, in this release, all past
> releases, and all future releases, not only in Python, but in any
> software.

Given that there is a long document showing the changes in each Python
release, I would hope all intended changes of significance would be
listed. Of course mistakes can happen, which was why I posted in the
first place.

I have no plans to track down the exact change in Python code that
caused this. There does not seem to be much point, since according to
Fredrik this seems to be an area that is practically undefined and the
M2Crypto code was clearly buggy.

-- 
  Heikki Toivonen