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PyObject_HEAD's documentation in py3k (http://docs.python.org/dev/py3k/c-api/structures.html#PyObject_HEAD) uses the same content used in the python 2.x's docs which is wrong, as there were some API changes.
PyObject_HEAD is actually defined as
#define PyObject_HEAD PyObject ob_base;
with PyObject defined as
typedef struct _object {
 _PyObject_HEAD_EXTRA
 Py_ssize_t ob_refcnt;
 struct _typeobject *ob_type;
} PyObject;
(The PyTRACE_REFS discussion is still valid, though.)
Additionally, it'd be nice to mention that the Py_REFCNT(ob) and Py_TYPE(ob) macros should be used to access the PyObject members.

Additionally, I prefer move the discussion of Py_TRACE_REFS under the documentation of PyObject: http://docs.python.org/dev/py3k/c-api/structures.html?highlight=pyobject_head#PyObject, since they'are connected directly. The doc of PyObject_HEAD should only saying like "expands to a PyObject variable".

PEP 3123 is the one that describes this change. I'm submitting a file with the proposed changes to the docs.

Did you intend to remove the discussion of Py_TRACE_REFS completely? (I've reworked your patch a little bit, adding some markup such as :c:macro:`Py_REFCNT`.)

New changeset 760c5cfacbaa by Gregory P. Smith in branch '3.4':
issue9014: Properly document PyObject_HEAD and friends post-PEP-3123.
https://hg.python.org/cpython/rev/760c5cfacbaa
New changeset 7dc8f0075d60 by Gregory P. Smith in branch 'default':
issue9014: Properly document PyObject_HEAD and friends post-PEP-3123.
https://hg.python.org/cpython/rev/7dc8f0075d60 

i used wiggin15's patch to start with. I'm now looking at akuchling's patch and will incorporate any additional things it adds (I missed that earlier).

The markup is not a huge deal, I think. I also did some bits of rewording that can probably be ignored. The TRACE_REFS question is the only important one, I think.

New changeset 752ea0acc37e by Gregory P. Smith in branch '3.4':
issue9014: Include more formatting on :c:type:`PyObject` etc.
https://hg.python.org/cpython/rev/752ea0acc37e
New changeset 78a2d1169be1 by Gregory P. Smith in branch 'default':
issue9014: Include more formatting on :c:type:`PyObject` etc.
https://hg.python.org/cpython/rev/78a2d1169be1 

We no longer describe the contents of PyObject in the docs so mentioning Py_TRACE_REFS does not seem worth it as that just changes Py_HEAD_EXTRA which adds the doubly linked list to PyObject (today).
Py_TRACE_REFS isn't useful for anyone to know about IMNSHO as it's a compile time define that normally comes from choosing to do a pydebug build. (I believe we have or have at least had bugs in our code where Py_TRACE_REFS won't work if Py_DEBUG is not also defined as we never test in such a mixed non-DEBUG but with TRACE_REFS configuration)