PyCheck for a classes defined in python and user data in PyObject_HEAD

sndive at gmail.com sndive at gmail.com
Sat Nov 17 00:22:46 CET 2007


On Nov 15, 10:00 pm, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
wrote:
> En Fri, 16 Nov 2007 00:27:42 -0300, <snd... at gmail.com> escribió:
>
>
>
> > On Nov 1, 11:04 pm, "Gabriel Genellina" <gagsl-... at yahoo.com.ar>
> > wrote:
> >> En Thu, 01 Nov 2007 22:13:35 -0300, <snd... at gmail.com> escribió:
> >> >> I'm in a situation when i don't really need to extend python with any
> >> >> classes of my own but
> >> >> i do have extra luggage for the python data structures such as
> >> tuples,
> >> >> lists, dictionaries, etc
> >> >> on the c++ side. I see no place in PyObject_HEAD where i can stick a
> >> >> void* to my extra data.
>
> >> Assuming you can recompile all the extensions you use, you could insert
> >> your void* into _PyObject_HEAD_EXTRA and _PyObject_EXTRA_INIT
>
> > i added two void pointers to head_extra and 0,0, to the extra_init.
> > For some reason i get garbage in them from PyEval_EvalCode :-(
> > (that's after i blew the build dir and rebuilt 2.4.4 from scratch
> > so i don't think i have a bad build)
>
> Can't you use instead the other approaches suggested on this thread? Like
> keeping a weakkey dictionary holding your additional attributes? Seems a
> lot safer to do that way.
>
> I've never changed that headers myself so I can't guarantee it works.
> Perhaps there are some assumptions somewhere in the code about a specific
> layout. But since _PyObject_HEAD_EXTRA is used in the debug build I think
> you should be able to add your own fields, at least in principle...

i finally found that i need to reset my fields in _Py_NewReference(op)
also.
weakref approach won't work for me because i need extra data in lists/
dictionaries/tuples in addition to instances of classes
(all instances of all classes: can't derive and essentially
make my own bloated psl to maintain)

> Remember that this change invalidates ALL binaries for ANY library or
> extension you may be using. An additional check might be to change the

that's not a problem since i build with a prefix other than /usr/local
and the target is an embedded system so i have full control over
the environment (until someone cracks it :-)

i finally got most of the code working after i figured out that
HEAD_INIT is ignored by tuple allocation code, etc
and _Py_NewReference has to be modified.

thank all of you for all the help. you got me unstuck.



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