[Python-3000] Impact of Py_FindMethod removal on external API's

[Amaury Forgeot d'Arc]

Hello,

Campbell Barton wrote:
> Hey there, Recently I started to write a new python/C api for
> Blender3D with python3.0rc3.
> This PyApi is a thin wrapper for an autogenerated C API to be used by
> the UI and animation system  (all in C).
>
> Without going into too many details, Im using tp_getattr so the
> requested attribute can be forwarded to our internal functions.
> The Blender3D game engine that has used this method to wrap internal
> data for some years as well, so I don't think this is that unusual.
>
> We moved most of our api's to use tp_getset, but that only works when
> the attributes you need dont change.
>
> Quote...
> http://mail.python.org/pipermail/python-3000/2008-July/014303.html
>> The primary use of Py_FindMethod was to implement a tp_getattr slot
>> handler. Now that it has been removed, there is nothing remaining in
>> the py3k codebase that actually uses the tp_getattr slot!
>
>> It has been 12 years since tp_getattro was introduced. Is it time to
>> finally phase out tp_getattr?
>
> I have no problems with breaking compatibility for python3000, however
> in this case removal of Py_FindMethod, removes functionality for
> external C api's that rely on dynamic attributes with tp_getattr.
>
> Is the intention to remove support for tp_getattr altogether?
>
> Note - in the meantime Ill add our own version of Py_FindMethod but
> its not ideal.

The same functionality can be achieved with the tp_getattro slot:
implement your special dynamic attributes there, and then call
PyObject_GenericGetAttr for the default behavior.

You may have a look at the implementation of the pyexpat module:
Modules/pyexpat.c, function xmlparse_getattro

-- 
Amaury Forgeot d'Arc