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bpo-44263: Better explain the GC contract for PyType_FromSpecWithBases (GH-26442)

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(cherry picked from commit 8b55bc3f93)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
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Miss Islington (bot) 2021-05-28 20:20:54 -07:00 • committed by GitHub
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11
Doc/c-api/gcsupport.rst
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@ -33,6 +33,17 @@ Constructors for container types must conform to two rules:
#. Once all the fields which may contain references to other containers are #. Once all the fields which may contain references to other containers are
initialized, it must call :c:func:`PyObject_GC_Track`. initialized, it must call :c:func:`PyObject_GC_Track`.
.. warning::
If a type adds the Py_TPFLAGS_HAVE_GC, then it *must* implement at least
a :c:member:`~PyTypeObject.tp_traverse` handler or explicitly use one
from its subclass or subclasses.
Some APIs like :c:func:`PyType_FromSpecWithBases` or
:c:func:`PyType_FromSpec` will automatically populate the
:c:member:`~PyTypeObject.tp_flags`, :c:member:`~PyTypeObject.tp_traverse`
and :c:member:`~PyTypeObject.tp_clear` fields if the type inherits from a
class that implements the garbage collector protocol and the child class
does *not* include the :const:`Py_TPFLAGS_HAVE_GC` flag.
.. c:function:: TYPE* PyObject_GC_New(TYPE, PyTypeObject *type) .. c:function:: TYPE* PyObject_GC_New(TYPE, PyTypeObject *type)

7
Doc/c-api/type.rst
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@ -168,6 +168,13 @@ The following functions and structs are used to create
The associated module is not inherited by subclasses; it must be specified The associated module is not inherited by subclasses; it must be specified
for each class individually. for each class individually.
If some of the bases in *bases* implements the GC protocol and the type being
created does not include the :const:`Py_TPFLAGS_HAVE_GC` in the flags included in
*spec*, then the GC protocol will be automatically implemented from its parents. On
the contrary, if the type being created does include :const:`Py_TPFLAGS_HAVE_GC` in
its flags then it *must* implement the GC protocol itself by at least including a slot
for :c:member:`~PyTypeObject.tp_traverse` in *spec*.
This function calls :c:func:`PyType_Ready` on the new type. This function calls :c:func:`PyType_Ready` on the new type.
.. versionadded:: 3.9 .. versionadded:: 3.9