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Issue #23710: Update PyObject_HEAD documentation

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Since PEP 3123, PyObject_HEAD only has one field named ob_base.
Users now need to use the Py_TYPE macro instead of self->ob_type.

Initial patch by Ammar Askar.
This commit is contained in:
Berker Peksag 2016-08-03 12:58:49 +03:00
parent 9de620e970
commit bed6891c77
1 changed files with 9 additions and 5 deletions
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14
Doc/extending/newtypes.rst
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@ -52,11 +52,15 @@ The first bit that will be new is::
} noddy_NoddyObject;
This is what a Noddy object will contain---in this case, nothing more than what
every Python object contains---a refcount and a pointer to a type object.
These are the fields the ``PyObject_HEAD`` macro brings in. The reason for the
macro is to standardize the layout and to enable special debugging fields in
debug builds. Note that there is no semicolon after the ``PyObject_HEAD``
macro; one is included in the macro definition. Be wary of adding one by
every Python object contains---a field called ``ob_base`` of type
:c:type:`PyObject`. :c:type:`PyObject` in turn, contains an ``ob_refcnt``
field and a pointer to a type object. These can be accessed using the macros
:c:macro:`Py_REFCNT` and :c:macro:`Py_TYPE` respectively. These are the fields
the :c:macro:`PyObject_HEAD` macro brings in. The reason for the macro is to
standardize the layout and to enable special debugging fields in debug builds.
Note that there is no semicolon after the :c:macro:`PyObject_HEAD` macro;
one is included in the macro definition. Be wary of adding one by
accident; it's easy to do from habit, and your compiler might not complain,
but someone else's probably will! (On Windows, MSVC is known to call this an
error and refuse to compile the code.)