[Cython] CEP 1001 - Custom PyTypeObject extensions

[Robert Bradshaw]

On Mon, May 14, 2012 at 10:05 AM, Nathaniel Smith <njs at pobox.com> wrote:
> On Mon, May 14, 2012 at 3:23 PM, Dag Sverre Seljebotn
> <d.s.seljebotn at astro.uio.no> wrote:
>> On 05/14/2012 01:34 PM, Stefan Behnel wrote:
>>>
>>> Dag Sverre Seljebotn, 13.05.2012 21:37:
>>>>
>>>> Anyway, thanks for the heads up, this seems to need a bit more work.
>>>> Input
>>>> from somebody more familiar with this corner of the CPython API very
>>>> welcome.
>>>
>>>
>>> Wouldn't you consider python-dev an appropriate place to discuss this?
>>
>>
>> Propose something for a PEP that's primarily useful to Cython without even
>> understanding the full implications myself first?
>>
>> I'd rather try to not annoy people; I figured the time I have the CPython
>> patches ready and tested is the time I ping python-dev...
>
> If you want to eventually propose a PEP, you really really really
> should be talking to them before. Otherwise you'll get everything
> worked out just the way you want and they'll be like "what is this?
> re-do it all totally differently". And they might be wrong, but then
> you have to reconstruct for them the whole debate and reasoning
> process and implicit assumptions that you're making and not realizing
> you need to articulate, so easier to just get all the interested
> people at the table to begin with. And they might be right, in which
> case you just wasted however much time digging yourself into a hole
> and reverse-engineering bits of CPython.
>
> Don't propose it as a PEP, just say "hey, we have this problem and
> these constraints, and we're thinking we could solve them by something
> like this; but of course that has these limitations, so I dunno. What
> do you think?" And expect to spend some time figuring out what your
> requirements actually are (even if you think you know already, see
> above about implicit assumptions).

I personally think it's a great idea to bounce ideas around here first
before going to python-dev, especially as a PEP wouldn't get in until
3.3 or 3.4 at best, and we want to do something with 2.4+ in the near
term. That doesn't preclude presenting the problem and proposed
solution on python-dev as well, but the purpose of this thread seems
to be to think about it some, including how we're going to support
things in the short term, not nail down an exact PEP for Python to
accept at face value. I think we're at a point we can ping python-dev
now though.

To be more futureproof, we'd want an offset to PyExtendedTypeObject
rather than assuming it exists at the end of PyTypeObject, but I don't
see a good place to store this information, so assuming it's right
there based on a bit in the flag seems a reasonable way forward.

- Robert