[Cython] inspect.isbuiltin(cyfunction) and inheritance from PyCFunction

[Stefan Behnel]

Stefan Behnel, 01.02.2014 17:04:
> Stefan Behnel, 31.01.2014 21:01:
>> Yury Selivanov just committed a revised version of a patch I wrote for
>> CPython's inspect module last year. It now accepts Cython's function type
>> as Python function, based on the function-like attributes that it exports.
>>
>> http://hg.python.org/cpython/rev/32a660a52aae
>>
>> That means that things like inspect.signature(cyfunction) will also work
>> now, and finally have a reason to be further improved, including parameter
>> introspection, annotations, etc. :)
> 
> Sorry, huge correction: inspect.isfunction(cyfunction) still returns False.
> Only introspection and signature analysis in the inspect module were
> changed. I got it wrong because I had code in my usersitecustomize.py that
> monkey patches inspect.isfunction(), and had completely forgotten about it.
> 
> Looking through this a bit more, I noticed that CyFunction inherits from
> PyCFunction, but doesn't actually tell CPython that it does. If I add this
> line to __Pyx_CyFunction_init(), before the PyType_Ready() call:
> 
>     __pyx_CyFunctionType_type.tp_base = &PyCFunction_Type;
> 
> it still works as expected, but inspect.isbuiltin() now returns True (as
> expected). Does anyone see a reason why we should not be doing this?

Tried it, found a reason. It makes CPython inherit some slot functions from
the base type, specifically tp_hash and tp_richompare, and those don't work
with the cyfunction type. Meaning, we'd have to implement those explicitly
to override the base type's implementations.

Stefan