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gh-60074: add new stable API function PyType_FromMetaclass #93012

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Merged
encukou merged 6 commits into from
May 27, 2022
Merged

gh-60074: add new stable API function PyType_FromMetaclass #93012

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05940a8
gh-60074: add new stable API function PyType_FromMetaclass
wjakob May 20, 2022
30e4e1b
retarget to Python 3.12
wjakob May 24, 2022
0525d78
incorporated feedback
wjakob May 25, 2022
db62080
.. also remove unnecessary indirection from implementation
wjakob May 25, 2022
b4a478c
fix Py_LIMITED_API check in object.h
wjakob May 25, 2022
872249e
Style nitpick
encukou May 26, 2022
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@wjakob
wjakob committed May 25, 2022
commit 0525d785f19e487cedac494a63c1f892f6a91450
31 changes: 15 additions & 16 deletions Doc/c-api/type.rst
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Expand Up @@ -190,11 +190,16 @@ Creating Heap-Allocated Types
The following functions and structs are used to create
:ref:`heap types <heap-types>`.

.. c:function:: PyObject* PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
.. c:function:: PyObject* PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, PyType_Spec *spec, PyObject *bases)

Create and return a :ref:`heap type <heap-types>` from the *spec*
(:const:`Py_TPFLAGS_HEAPTYPE`).

The metaclass *metaclass* is used to construct the resulting type object.
When *metaclass* is ``NULL``, the default :c:type:`PyType_Type` is used
instead. Note that metaclasses that override
:c:member:`~PyTypeObject.tp_new` are not supported.

The *bases* argument can be used to specify base classes; it can either
be only one class or a tuple of classes.
If *bases* is ``NULL``, the *Py_tp_bases* slot is used instead.
Expand All @@ -208,9 +213,13 @@ The following functions and structs are used to create
The associated module is not inherited by subclasses; it must be specified
for each class individually.

This function calls :c:func:`PyType_Ready` on the new type. Its behavior is
equivalent to ``PyType_FromMetaclass(&PyType_Type, NULL, spec,
bases)``.
This function calls :c:func:`PyType_Ready` on the new type.

.. versionadded:: 3.12

.. c:function:: PyObject* PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)

Equivalent to ``PyType_FromMetaclass(NULL, module, spec, bases)``.

.. versionadded:: 3.9

Expand All @@ -219,26 +228,16 @@ The following functions and structs are used to create
The function now accepts a single class as the *bases* argument and
``NULL`` as the ``tp_doc`` slot.

.. c:function:: PyObject* PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, PyType_Spec *spec, PyObject *bases)

Create and return a :ref:`heap type <heap-types>` from the *spec*
(:const:`Py_TPFLAGS_HEAPTYPE`). This function is a generalization of
:c:func:`PyType_FromModuleAndSpec`, with the main difference being that
the metaclass *metaclass* is used to construct the resulting type object.

Metaclasses that override :c:member:`~PyTypeObject.tp_new` are not supported.

.. versionadded:: 3.12

.. c:function:: PyObject* PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)

Equivalent to ``PyType_FromModuleAndSpec(NULL, spec, bases)``.
Equivalent to ``PyType_FromMetaclass(NULL, NULL, spec, bases)``.

.. versionadded:: 3.3

.. c:function:: PyObject* PyType_FromSpec(PyType_Spec *spec)

Equivalent to ``PyType_FromSpecWithBases(spec, NULL)``.
Equivalent to ``PyType_FromMetaclass(NULL, NULL, spec, NULL)``.

.. c:type:: PyType_Spec

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5 changes: 4 additions & 1 deletion Objects/typeobject.c
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Expand Up @@ -3374,7 +3374,7 @@ PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
PyObject *
PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
{
return PyType_FromMetaclass(&PyType_Type, module, spec, bases);
return PyType_FromMetaclass(NULL, module, spec, bases);
}

PyObject *
Expand All @@ -3391,6 +3391,9 @@ PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module,
char *res_start;
short slot_offset, subslot_offset;

if (!metaclass)
metaclass = &PyType_Type;
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if (metaclass->tp_new != PyType_Type.tp_new) {
PyErr_SetString(PyExc_TypeError,
"Metaclasses with custom tp_new are not supported.");
Expand Down