[Python-Dev] signature object issues (to discuss while I am out of contact)

[Aahz]

On Mon, May 01, 2006, Brett Cannon wrote:
> On 5/1/06, Aahz <aahz at pythoncraft.com> wrote:
>>On Mon, May 01, 2006, Brett Cannon wrote:
>>>
>>> But there are two things that I can't quite decide upon.
>>>
>>> One is whether a signature object should be automatically created
>>> for every function.  As of right now the PEP I am drafting has it
>>> on a per-need basis and have it assigned to __signature__ through
>>> a built-in function or putting it 'inspect'.  Now automatically
>>> creating the object would possibly make it more useful, but it
>>> could also be considered overkill.  Also not doing it automatically
>>> allows signature objects to possibly make more sense for classes (to
>>> represent __init__) and instances (to represent __call__).  But having
>>> that same support automatically feels off for some reason to me.
>>
>>My take is that we should do it automatically and provide a helper
>>function that does additional work.  The class case is already
>>complicated by __new__(); we probably don't want to automatically sort
>>out __init__() vs __new__(), but I think we do want regular functions and
>>methods to automatically have a __signature__ attribute.  Aside from the
>>issue with classes, are there any other drawbacks to automatically
>>creating __signature__?
> 
> Well, one issue is the dichotomy between Python and C functions not
> both providing a signature object.  There is no good way to provide a
> signature object automatically for C functions (at least at the
> moment; could add the signature string for PyArg_ParseTuple() to the
> PyMethodDef and have it passed in to the wrapped C function so that
> initialization of the class can get to the parameters string).  So you
> can't fully rely on the object being available for all functions and
> methods unless a worthless signature object is placed for C functions.

>From my POV, that suggests changing the C API rather than not having
automatic signatures.  That probably requires Py3K, though.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

"Argue for your limitations, and sure enough they're yours."  --Richard Bach