typeobj.rst

.. highlight:: c

.. _type-structs:

Type Object Structures
======================

Perhaps one of the most important structures of the Python object system is the
structure that defines a new type: the :c:type:`PyTypeObject` structure.  Type
objects can be handled using any of the ``PyObject_*`` or
``PyType_*`` functions, but do not offer much that's interesting to most
Python applications. These objects are fundamental to how objects behave, so
they are very important to the interpreter itself and to any extension module
that implements new types.

Type objects are fairly large compared to most of the standard types. The reason
for the size is that each type object stores a large number of values, mostly C
function pointers, each of which implements a small part of the type's
functionality.  The fields of the type object are examined in detail in this
section.  The fields will be described in the order in which they occur in the
structure.

In addition to the following quick reference, the :ref:`typedef-examples`
section provides at-a-glance insight into the meaning and use of
:c:type:`PyTypeObject`.


Quick Reference
---------------

.. _tp-slots-table:

"tp slots"
^^^^^^^^^^

.. table::
   :widths: 18,18,18,1,1,1,1

   +------------------------------------------------+-----------------------------------+-------------------+---------------+
   | PyTypeObject Slot [#slots]_                    | :ref:`Type <slot-typedefs-table>` | special           | Info [#cols]_ |
   |                                                |                                   | methods/attrs     +---+---+---+---+
   |                                                |                                   |                   | O | T | D | I |
   +================================================+===================================+===================+===+===+===+===+
   | <R> :c:member:`~PyTypeObject.tp_name`          | const char *                      | __name__          | X | X |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_basicsize`         | :c:type:`Py_ssize_t`              |                   | X | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_itemsize`          | :c:type:`Py_ssize_t`              |                   |   | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_dealloc`           | :c:type:`destructor`              |                   | X | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_vectorcall_offset` | :c:type:`Py_ssize_t`              |                   |   | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | (:c:member:`~PyTypeObject.tp_getattr`)         | :c:type:`getattrfunc`             | __getattribute__, |   |   |   | G |
   |                                                |                                   | __getattr__       |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | (:c:member:`~PyTypeObject.tp_setattr`)         | :c:type:`setattrfunc`             | __setattr__,      |   |   |   | G |
   |                                                |                                   | __delattr__       |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_as_async`          | :c:type:`PyAsyncMethods` *        | :ref:`sub-slots`  |   |   |   | % |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_repr`              | :c:type:`reprfunc`                | __repr__          | X | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_as_number`         | :c:type:`PyNumberMethods` *       | :ref:`sub-slots`  |   |   |   | % |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_as_sequence`       | :c:type:`PySequenceMethods` *     | :ref:`sub-slots`  |   |   |   | % |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_as_mapping`        | :c:type:`PyMappingMethods` *      | :ref:`sub-slots`  |   |   |   | % |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_hash`              | :c:type:`hashfunc`                | __hash__          | X |   |   | G |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_call`              | :c:type:`ternaryfunc`             | __call__          |   | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_str`               | :c:type:`reprfunc`                | __str__           | X |   |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_getattro`          | :c:type:`getattrofunc`            | __getattribute__, | X | X |   | G |
   |                                                |                                   | __getattr__       |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_setattro`          | :c:type:`setattrofunc`            | __setattr__,      | X | X |   | G |
   |                                                |                                   | __delattr__       |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_as_buffer`         | :c:type:`PyBufferProcs` *         | :ref:`sub-slots`  |   |   |   | % |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_flags`             | unsigned long                     |                   | X | X |   | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_doc`               | const char *                      | __doc__           | X | X |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_traverse`          | :c:type:`traverseproc`            |                   |   | X |   | G |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_clear`             | :c:type:`inquiry`                 |                   |   | X |   | G |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_richcompare`       | :c:type:`richcmpfunc`             | __lt__,           | X |   |   | G |
   |                                                |                                   | __le__,           |   |   |   |   |
   |                                                |                                   | __eq__,           |   |   |   |   |
   |                                                |                                   | __ne__,           |   |   |   |   |
   |                                                |                                   | __gt__,           |   |   |   |   |
   |                                                |                                   | __ge__            |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | (:c:member:`~PyTypeObject.tp_weaklistoffset`)  | :c:type:`Py_ssize_t`              |                   |   | X |   | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_iter`              | :c:type:`getiterfunc`             | __iter__          |   |   |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_iternext`          | :c:type:`iternextfunc`            | __next__          |   |   |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_methods`           | :c:type:`PyMethodDef` []          |                   | X | X |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_members`           | :c:type:`PyMemberDef` []          |                   |   | X |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_getset`            | :c:type:`PyGetSetDef` []          |                   | X | X |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_base`              | :c:type:`PyTypeObject` *          | __base__          |   |   | X |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_dict`              | :c:type:`PyObject` *              | __dict__          |   |   | ? |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_descr_get`         | :c:type:`descrgetfunc`            | __get__           |   |   |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_descr_set`         | :c:type:`descrsetfunc`            | __set__,          |   |   |   | X |
   |                                                |                                   | __delete__        |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | (:c:member:`~PyTypeObject.tp_dictoffset`)      | :c:type:`Py_ssize_t`              |                   |   | X |   | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_init`              | :c:type:`initproc`                | __init__          | X | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_alloc`             | :c:type:`allocfunc`               |                   | X |   | ? | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_new`               | :c:type:`newfunc`                 | __new__           | X | X | ? | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_free`              | :c:type:`freefunc`                |                   | X | X | ? | ? |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_is_gc`             | :c:type:`inquiry`                 |                   |   | X |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | <:c:member:`~PyTypeObject.tp_bases`>           | :c:type:`PyObject` *              | __bases__         |   |   | ~ |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | <:c:member:`~PyTypeObject.tp_mro`>             | :c:type:`PyObject` *              | __mro__           |   |   | ~ |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | [:c:member:`~PyTypeObject.tp_cache`]           | :c:type:`PyObject` *              |                   |   |   |       |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | [:c:member:`~PyTypeObject.tp_subclasses`]      | void *                            | __subclasses__    |   |   |       |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | [:c:member:`~PyTypeObject.tp_weaklist`]        | :c:type:`PyObject` *              |                   |   |   |       |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | (:c:member:`~PyTypeObject.tp_del`)             | :c:type:`destructor`              |                   |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | [:c:member:`~PyTypeObject.tp_version_tag`]     | unsigned int                      |                   |   |   |       |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_finalize`          | :c:type:`destructor`              | __del__           |   |   |   | X |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | :c:member:`~PyTypeObject.tp_vectorcall`        | :c:type:`vectorcallfunc`          |                   |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+
   | [:c:member:`~PyTypeObject.tp_watched`]         | unsigned char                     |                   |   |   |   |   |
   +------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+

.. [#slots]

   **()**: A slot name in parentheses indicates it is (effectively) deprecated.

   **<>**: Names in angle brackets should be initially set to ``NULL`` and
   treated as read-only.

   **[]**: Names in square brackets are for internal use only.

   **<R>** (as a prefix) means the field is required (must be non-``NULL``).

.. [#cols] Columns:

   **"O"**:  set on :c:data:`PyBaseObject_Type`

   **"T"**:  set on :c:data:`PyType_Type`

   **"D"**:  default (if slot is set to ``NULL``)

   .. code-block:: none

      X - PyType_Ready sets this value if it is NULL
      ~ - PyType_Ready always sets this value (it should be NULL)
      ? - PyType_Ready may set this value depending on other slots

      Also see the inheritance column ("I").

   **"I"**:  inheritance

   .. code-block:: none

      X - type slot is inherited via *PyType_Ready* if defined with a *NULL* value
      % - the slots of the sub-struct are inherited individually
      G - inherited, but only in combination with other slots; see the slot's description
      ? - it's complicated; see the slot's description

   Note that some slots are effectively inherited through the normal
   attribute lookup chain.

.. _sub-slots:

sub-slots
^^^^^^^^^

.. table::
   :widths: 26,17,12

   +---------------------------------------------------------+-----------------------------------+---------------+
   | Slot                                                    | :ref:`Type <slot-typedefs-table>` | special       |
   |                                                         |                                   | methods       |
   +=========================================================+===================================+===============+
   | :c:member:`~PyAsyncMethods.am_await`                    | :c:type:`unaryfunc`               | __await__     |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyAsyncMethods.am_aiter`                    | :c:type:`unaryfunc`               | __aiter__     |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyAsyncMethods.am_anext`                    | :c:type:`unaryfunc`               | __anext__     |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyAsyncMethods.am_send`                     | :c:type:`sendfunc`                |               |
   +---------------------------------------------------------+-----------------------------------+---------------+
   |                                                                                                             |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_add`                     | :c:type:`binaryfunc`              | __add__       |
   |                                                         |                                   | __radd__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_add`             | :c:type:`binaryfunc`              | __iadd__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_subtract`                | :c:type:`binaryfunc`              | __sub__       |
   |                                                         |                                   | __rsub__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_subtract`        | :c:type:`binaryfunc`              | __isub__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_multiply`                | :c:type:`binaryfunc`              | __mul__       |
   |                                                         |                                   | __rmul__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_multiply`        | :c:type:`binaryfunc`              | __imul__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_remainder`               | :c:type:`binaryfunc`              | __mod__       |
   |                                                         |                                   | __rmod__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_remainder`       | :c:type:`binaryfunc`              | __imod__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_divmod`                  | :c:type:`binaryfunc`              | __divmod__    |
   |                                                         |                                   | __rdivmod__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_power`                   | :c:type:`ternaryfunc`             | __pow__       |
   |                                                         |                                   | __rpow__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_power`           | :c:type:`ternaryfunc`             | __ipow__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_negative`                | :c:type:`unaryfunc`               | __neg__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_positive`                | :c:type:`unaryfunc`               | __pos__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_absolute`                | :c:type:`unaryfunc`               | __abs__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_bool`                    | :c:type:`inquiry`                 | __bool__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_invert`                  | :c:type:`unaryfunc`               | __invert__    |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_lshift`                  | :c:type:`binaryfunc`              | __lshift__    |
   |                                                         |                                   | __rlshift__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_lshift`          | :c:type:`binaryfunc`              | __ilshift__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_rshift`                  | :c:type:`binaryfunc`              | __rshift__    |
   |                                                         |                                   | __rrshift__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_rshift`          | :c:type:`binaryfunc`              | __irshift__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_and`                     | :c:type:`binaryfunc`              | __and__       |
   |                                                         |                                   | __rand__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_and`             | :c:type:`binaryfunc`              | __iand__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_xor`                     | :c:type:`binaryfunc`              | __xor__       |
   |                                                         |                                   | __rxor__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_xor`             | :c:type:`binaryfunc`              | __ixor__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_or`                      | :c:type:`binaryfunc`              | __or__        |
   |                                                         |                                   | __ror__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_or`              | :c:type:`binaryfunc`              | __ior__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_int`                     | :c:type:`unaryfunc`               | __int__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_reserved`                | void *                            |               |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_float`                   | :c:type:`unaryfunc`               | __float__     |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_floor_divide`            | :c:type:`binaryfunc`              | __floordiv__  |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_floor_divide`    | :c:type:`binaryfunc`              | __ifloordiv__ |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_true_divide`             | :c:type:`binaryfunc`              | __truediv__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_true_divide`     | :c:type:`binaryfunc`              | __itruediv__  |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_index`                   | :c:type:`unaryfunc`               | __index__     |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_matrix_multiply`         | :c:type:`binaryfunc`              | __matmul__    |
   |                                                         |                                   | __rmatmul__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyNumberMethods.nb_inplace_matrix_multiply` | :c:type:`binaryfunc`              | __imatmul__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   |                                                                                                             |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyMappingMethods.mp_length`                 | :c:type:`lenfunc`                 | __len__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyMappingMethods.mp_subscript`              | :c:type:`binaryfunc`              | __getitem__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyMappingMethods.mp_ass_subscript`          | :c:type:`objobjargproc`           | __setitem__,  |
   |                                                         |                                   | __delitem__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   |                                                                                                             |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_length`                | :c:type:`lenfunc`                 | __len__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_concat`                | :c:type:`binaryfunc`              | __add__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_repeat`                | :c:type:`ssizeargfunc`            | __mul__       |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_item`                  | :c:type:`ssizeargfunc`            | __getitem__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_ass_item`              | :c:type:`ssizeobjargproc`         | __setitem__   |
   |                                                         |                                   | __delitem__   |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_contains`              | :c:type:`objobjproc`              | __contains__  |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_inplace_concat`        | :c:type:`binaryfunc`              | __iadd__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PySequenceMethods.sq_inplace_repeat`        | :c:type:`ssizeargfunc`            | __imul__      |
   +---------------------------------------------------------+-----------------------------------+---------------+
   |                                                                                                             |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyBufferProcs.bf_getbuffer`                 | :c:func:`getbufferproc`           | __buffer__    |
   +---------------------------------------------------------+-----------------------------------+---------------+
   | :c:member:`~PyBufferProcs.bf_releasebuffer`             | :c:func:`releasebufferproc`       | __release_\   |
   |                                                         |                                   | buffer\__     |
   +---------------------------------------------------------+-----------------------------------+---------------+

.. _slot-typedefs-table:

slot typedefs
^^^^^^^^^^^^^

+-----------------------------+-----------------------------+----------------------+
| typedef                     | Parameter Types             | Return Type          |
+=============================+=============================+======================+
| :c:type:`allocfunc`         | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyTypeObject` * |                      |
|                             |    :c:type:`Py_ssize_t`     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`destructor`        | :c:type:`PyObject` *        | void                 |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`freefunc`          | void *                      | void                 |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`traverseproc`      | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`visitproc`      |                      |
|                             |    void *                   |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`newfunc`           | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyTypeObject` * |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`initproc`          | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`reprfunc`          | :c:type:`PyObject` *        | :c:type:`PyObject` * |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`getattrfunc`       | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    const char *             |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`setattrfunc`       | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    const char *             |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`getattrofunc`      | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`setattrofunc`      | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`descrgetfunc`      | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`descrsetfunc`      | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`hashfunc`          | :c:type:`PyObject` *        | Py_hash_t            |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`richcmpfunc`       | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    int                      |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`getiterfunc`       | :c:type:`PyObject` *        | :c:type:`PyObject` * |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`iternextfunc`      | :c:type:`PyObject` *        | :c:type:`PyObject` * |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`lenfunc`           | :c:type:`PyObject` *        | :c:type:`Py_ssize_t` |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`getbufferproc`     | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`Py_buffer` *    |                      |
|                             |    int                      |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`releasebufferproc` | .. line-block::             | void                 |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`Py_buffer` *    |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`inquiry`           | :c:type:`PyObject` *        | int                  |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`unaryfunc`         | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`binaryfunc`        | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`ternaryfunc`       | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`ssizeargfunc`      | .. line-block::             | :c:type:`PyObject` * |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`Py_ssize_t`     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`ssizeobjargproc`   | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`Py_ssize_t`     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`objobjproc`        | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+
| :c:type:`objobjargproc`     | .. line-block::             | int                  |
|                             |                             |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
|                             |    :c:type:`PyObject` *     |                      |
+-----------------------------+-----------------------------+----------------------+

See :ref:`slot-typedefs` below for more detail.


PyTypeObject Definition
-----------------------

The structure definition for :c:type:`PyTypeObject` can be found in
:file:`Include/cpython/object.h`.  For convenience of reference, this repeats the
definition found there:

.. XXX Drop this?

.. literalinclude:: ../includes/typestruct.h


PyObject Slots
--------------

The type object structure extends the :c:type:`PyVarObject` structure. The
:c:member:`~PyVarObject.ob_size` field is used for dynamic types (created by :c:func:`!type_new`,
usually called from a class statement). Note that :c:data:`PyType_Type` (the
metatype) initializes :c:member:`~PyTypeObject.tp_itemsize`, which means that its instances (i.e.
type objects) *must* have the :c:member:`~PyVarObject.ob_size` field.


:c:member:`PyObject.ob_refcnt`

   The type object's reference count is initialized to ``1`` by the
   ``PyObject_HEAD_INIT`` macro.  Note that for :ref:`statically allocated type
   objects <static-types>`, the type's instances (objects whose :c:member:`~PyObject.ob_type`
   points back to the type) do *not* count as references.  But for
   :ref:`dynamically allocated type objects <heap-types>`, the instances *do*
   count as references.

   **Inheritance:**

   This field is not inherited by subtypes.


:c:member:`PyObject.ob_type`

   This is the type's type, in other words its metatype.  It is initialized by the
   argument to the ``PyObject_HEAD_INIT`` macro, and its value should normally be
   ``&PyType_Type``.  However, for dynamically loadable extension modules that must
   be usable on Windows (at least), the compiler complains that this is not a valid
   initializer.  Therefore, the convention is to pass ``NULL`` to the
   ``PyObject_HEAD_INIT`` macro and to initialize this field explicitly at the
   start of the module's initialization function, before doing anything else.  This
   is typically done like this::

      Foo_Type.ob_type = &PyType_Type;

   This should be done before any instances of the type are created.
   :c:func:`PyType_Ready` checks if :c:member:`~PyObject.ob_type` is ``NULL``, and if so,
   initializes it to the :c:member:`~PyObject.ob_type` field of the base class.
   :c:func:`PyType_Ready` will not change this field if it is non-zero.

   **Inheritance:**

   This field is inherited by subtypes.


PyVarObject Slots
-----------------

:c:member:`PyVarObject.ob_size`

   For :ref:`statically allocated type objects <static-types>`, this should be
   initialized to zero. For :ref:`dynamically allocated type objects
   <heap-types>`, this field has a special internal meaning.

   This field should be accessed using the :c:func:`Py_SIZE()` macro.

   **Inheritance:**

   This field is not inherited by subtypes.


PyTypeObject Slots
------------------

Each slot has a section describing inheritance.  If :c:func:`PyType_Ready`
may set a value when the field is set to ``NULL`` then there will also be
a "Default" section.  (Note that many fields set on :c:data:`PyBaseObject_Type`
and :c:data:`PyType_Type` effectively act as defaults.)

.. c:member:: const char* PyTypeObject.tp_name

   Pointer to a NUL-terminated string containing the name of the type. For types
   that are accessible as module globals, the string should be the full module
   name, followed by a dot, followed by the type name; for built-in types, it
   should be just the type name.  If the module is a submodule of a package, the
   full package name is part of the full module name.  For example, a type named
   :class:`!T` defined in module :mod:`!M` in subpackage :mod:`!Q` in package :mod:`!P`
   should have the :c:member:`~PyTypeObject.tp_name` initializer ``"P.Q.M.T"``.

   For :ref:`dynamically allocated type objects <heap-types>`,
   this should just be the type name, and
   the module name explicitly stored in the type dict as the value for key
   ``'__module__'``.

   For :ref:`statically allocated type objects <static-types>`,
   the *tp_name* field should contain a dot.
   Everything before the last dot is made accessible as the :attr:`~type.__module__`
   attribute, and everything after the last dot is made accessible as the
   :attr:`~type.__name__` attribute.

   If no dot is present, the entire :c:member:`~PyTypeObject.tp_name` field is made accessible as the
   :attr:`~type.__name__` attribute, and the :attr:`~type.__module__` attribute is undefined
   (unless explicitly set in the dictionary, as explained above).  This means your
   type will be impossible to pickle.  Additionally, it will not be listed in
   module documentations created with pydoc.

   This field must not be ``NULL``.  It is the only required field
   in :c:func:`PyTypeObject` (other than potentially
   :c:member:`~PyTypeObject.tp_itemsize`).

   **Inheritance:**

   This field is not inherited by subtypes.


.. c:member:: Py_ssize_t PyTypeObject.tp_basicsize
              Py_ssize_t PyTypeObject.tp_itemsize

   These fields allow calculating the size in bytes of instances of the type.

   There are two kinds of types: types with fixed-length instances have a zero
   :c:member:`!tp_itemsize` field, types with variable-length instances have a non-zero
   :c:member:`!tp_itemsize` field.  For a type with fixed-length instances, all
   instances have the same size, given in :c:member:`!tp_basicsize`.
   (Exceptions to this rule can be made using
   :c:func:`PyUnstable_Object_GC_NewWithExtraData`.)

   For a type with variable-length instances, the instances must have an
   :c:member:`~PyVarObject.ob_size` field, and the instance size is
   :c:member:`!tp_basicsize` plus N times :c:member:`!tp_itemsize`,
   where N is the "length" of the object.

   Functions like :c:func:`PyObject_NewVar` will take the value of N as an
   argument, and store in the instance's :c:member:`~PyVarObject.ob_size` field.
   Note that the :c:member:`~PyVarObject.ob_size` field may later be used for
   other purposes. For example, :py:type:`int` instances use the bits of
   :c:member:`~PyVarObject.ob_size` in an implementation-defined
   way; the underlying storage and its size should be accessed using
   :c:func:`PyLong_Export`.

   .. note::

      The :c:member:`~PyVarObject.ob_size` field should be accessed using
      the :c:func:`Py_SIZE()` and :c:func:`Py_SET_SIZE()` macros.

   Also, the presence of an :c:member:`~PyVarObject.ob_size` field in the
   instance layout doesn't mean that the instance structure is variable-length.
   For example, the :py:type:`list` type has fixed-length instances, yet those
   instances have a :c:member:`~PyVarObject.ob_size` field.
   (As with :py:type:`int`, avoid reading lists' :c:member:`!ob_size` directly.
   Call :c:func:`PyList_Size` instead.)

   The :c:member:`!tp_basicsize` includes size needed for data of the type's
   :c:member:`~PyTypeObject.tp_base`, plus any extra data needed
   by each instance.

   The  correct way to set :c:member:`!tp_basicsize` is to use the
   ``sizeof`` operator on the struct used to declare the instance layout.
   This struct must include the struct used to declare the base type.
   In other words, :c:member:`!tp_basicsize` must be greater than or equal
   to the base's :c:member:`!tp_basicsize`.

   Since every type is a subtype of :py:type:`object`, this struct must
   include :c:type:`PyObject` or :c:type:`PyVarObject` (depending on
   whether :c:member:`~PyVarObject.ob_size` should be included). These are
   usually defined by the macro :c:macro:`PyObject_HEAD` or
   :c:macro:`PyObject_VAR_HEAD`, respectively.

   The basic size does not include the GC header size, as that header is not
   part of :c:macro:`PyObject_HEAD`.

   For cases where struct used to declare the base type is unknown,
   see :c:member:`PyType_Spec.basicsize` and :c:func:`PyType_FromMetaclass`.

   Notes about alignment:

   - :c:member:`!tp_basicsize` must be a multiple of ``_Alignof(PyObject)``.
     When using ``sizeof`` on a ``struct`` that includes
     :c:macro:`PyObject_HEAD`, as recommended, the compiler ensures this.
     When not using a C ``struct``, or when using compiler
     extensions like ``__attribute__((packed))``, it is up to you.
   - If the variable items require a particular alignment,
     :c:member:`!tp_basicsize` and :c:member:`!tp_itemsize` must each be a
     multiple of that alignment.
     For example, if a type's variable part stores a ``double``, it is
     your responsibility that both fields are a multiple of
     ``_Alignof(double)``.

   **Inheritance:**

   These fields are inherited separately by subtypes.
   (That is, if the field is set to zero, :c:func:`PyType_Ready` will copy
   the value from the base type, indicating that the instances do not
   need additional storage.)

   If the base type has a non-zero :c:member:`~PyTypeObject.tp_itemsize`, it is generally not safe to set
   :c:member:`~PyTypeObject.tp_itemsize` to a different non-zero value in a subtype (though this
   depends on the implementation of the base type).


.. c:member:: destructor PyTypeObject.tp_dealloc

   .. corresponding-type-slot:: Py_tp_dealloc

   A pointer to the instance destructor function.  The function signature is::

      void tp_dealloc(PyObject *self);

   The destructor function should remove all references which the instance owns
   (e.g., call :c:func:`Py_CLEAR`), free all memory buffers owned by the
   instance, and call the type's :c:member:`~PyTypeObject.tp_free` function to
   free the object itself.

   If you may call functions that may set the error indicator, you must use
   :c:func:`PyErr_GetRaisedException` and :c:func:`PyErr_SetRaisedException`
   to ensure you don't clobber a preexisting error indicator (the deallocation
   could have occurred while processing a different error):

   .. code-block:: c

     static void
     foo_dealloc(foo_object *self)
     {
         PyObject *et, *ev, *etb;
         PyObject *exc = PyErr_GetRaisedException();
         ...
         PyErr_SetRaisedException(exc);
     }

   The dealloc handler itself must not raise an exception; if it hits an error
   case it should call :c:func:`PyErr_FormatUnraisable` to log (and clear) an
   unraisable exception.

   No guarantees are made about when an object is destroyed, except:

   * Python will destroy an object immediately or some time after the final
     reference to the object is deleted, unless its finalizer
     (:c:member:`~PyTypeObject.tp_finalize`) subsequently resurrects the
     object.
   * An object will not be destroyed while it is being automatically finalized
     (:c:member:`~PyTypeObject.tp_finalize`) or automatically cleared
     (:c:member:`~PyTypeObject.tp_clear`).

   CPython currently destroys an object immediately from :c:func:`Py_DECREF`
   when the new reference count is zero, but this may change in a future
   version.

   It is recommended to call :c:func:`PyObject_CallFinalizerFromDealloc` at the
   beginning of :c:member:`!tp_dealloc` to guarantee that the object is always
   finalized before destruction.

   If the type supports garbage collection (the :c:macro:`Py_TPFLAGS_HAVE_GC`
   flag is set), the destructor should call :c:func:`PyObject_GC_UnTrack`
   before clearing any member fields.

   It is permissible to call :c:member:`~PyTypeObject.tp_clear` from
   :c:member:`!tp_dealloc` to reduce code duplication and to guarantee that the
   object is always cleared before destruction.  Beware that
   :c:member:`!tp_clear` might have already been called.

   If the type is heap allocated (:c:macro:`Py_TPFLAGS_HEAPTYPE`), the
   deallocator should release the owned reference to its type object (via
   :c:func:`Py_DECREF`) after calling the type deallocator.  See the example
   code below.::

      static void
      foo_dealloc(PyObject *op)
      {
         foo_object *self = (foo_object *) op;
         PyObject_GC_UnTrack(self);
         Py_CLEAR(self->ref);
         Py_TYPE(self)->tp_free(self);
      }

   :c:member:`!tp_dealloc` must leave the exception status unchanged.  If it
   needs to call something that might raise an exception, the exception state
   must be backed up first and restored later (after logging any exceptions
   with :c:func:`PyErr_WriteUnraisable`).

   Example::

      static void
      foo_dealloc(PyObject *self)
      {
          PyObject *exc = PyErr_GetRaisedException();

          if (PyObject_CallFinalizerFromDealloc(self) < 0) {
              // self was resurrected.
              goto done;
          }

          PyTypeObject *tp = Py_TYPE(self);

          if (tp->tp_flags & Py_TPFLAGS_HAVE_GC) {
              PyObject_GC_UnTrack(self);
          }

          // Optional, but convenient to avoid code duplication.
          if (tp->tp_clear && tp->tp_clear(self) < 0) {
              PyErr_WriteUnraisable(self);
          }

          // Any additional destruction goes here.

          tp->tp_free(self);
          self = NULL;  // In case PyErr_WriteUnraisable() is called below.

          if (tp->tp_flags & Py_TPFLAGS_HEAPTYPE) {
              Py_CLEAR(tp);
          }

      done:
          // Optional, if something was called that might have raised an
          // exception.
          if (PyErr_Occurred()) {
              PyErr_WriteUnraisable(self);
          }
          PyErr_SetRaisedException(exc);
      }

   :c:member:`!tp_dealloc` may be called from
   any Python thread, not just the thread which created the object (if the
   object becomes part of a refcount cycle, that cycle might be collected by
   a garbage collection on any thread).  This is not a problem for Python
   API calls, since the thread on which :c:member:`!tp_dealloc` is called
   with an :term:`attached thread state`.  However, if the object being
   destroyed in turn destroys objects from some other C library, care
   should be taken to ensure that destroying those objects on the thread
   which called :c:member:`!tp_dealloc` will not violate any assumptions of
   the library.


   **Inheritance:**

   This field is inherited by subtypes.

   .. seealso::

      :ref:`life-cycle` for details about how this slot relates to other slots.


.. c:member:: Py_ssize_t PyTypeObject.tp_vectorcall_offset

   An optional offset to a per-instance function that implements calling
   the object using the :ref:`vectorcall protocol <vectorcall>`,
   a more efficient alternative
   of the simpler :c:member:`~PyTypeObject.tp_call`.

   This field is only used if the flag :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL`
   is set. If so, this must be a positive integer containing the offset in the
   instance of a :c:type:`vectorcallfunc` pointer.

   The *vectorcallfunc* pointer may be ``NULL``, in which case the instance behaves
   as if :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL` was not set: calling the instance
   falls back to :c:member:`~PyTypeObject.tp_call`.

   Any class that sets ``Py_TPFLAGS_HAVE_VECTORCALL`` must also set
   :c:member:`~PyTypeObject.tp_call` and make sure its behaviour is consistent
   with the *vectorcallfunc* function.
   This can be done by setting *tp_call* to :c:func:`PyVectorcall_Call`.

   .. versionchanged:: 3.8

      Before version 3.8, this slot was named ``tp_print``.
      In Python 2.x, it was used for printing to a file.
      In Python 3.0 to 3.7, it was unused.

   .. versionchanged:: 3.12

      Before version 3.12, it was not recommended for
      :ref:`mutable heap types <heap-types>` to implement the vectorcall
      protocol.
      When a user sets :attr:`~object.__call__` in Python code, only *tp_call* is
      updated, likely making it inconsistent with the vectorcall function.
      Since 3.12, setting ``__call__`` will disable vectorcall optimization
      by clearing the :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL` flag.

   **Inheritance:**

   This field is always inherited.
   However, the :c:macro:`Py_TPFLAGS_HAVE_VECTORCALL` flag is not
   always inherited. If it's not set, then the subclass won't use
   :ref:`vectorcall <vectorcall>`, except when
   :c:func:`PyVectorcall_Call` is explicitly called.


.. c:member:: getattrfunc PyTypeObject.tp_getattr

   .. corresponding-type-slot:: Py_tp_getattr

   An optional pointer to the get-attribute-string function.

   This field is deprecated.  When it is defined, it should point to a function
   that acts the same as the :c:member:`~PyTypeObject.tp_getattro` function, but taking a C string
   instead of a Python string object to give the attribute name.

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_getattr`, :c:member:`~PyTypeObject.tp_getattro`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_getattro`: a subtype
   inherits both :c:member:`~PyTypeObject.tp_getattr` and :c:member:`~PyTypeObject.tp_getattro` from its base type when
   the subtype's :c:member:`~PyTypeObject.tp_getattr` and :c:member:`~PyTypeObject.tp_getattro` are both ``NULL``.


.. c:member:: setattrfunc PyTypeObject.tp_setattr

   .. corresponding-type-slot:: Py_tp_setattr

   An optional pointer to the function for setting and deleting attributes.

   This field is deprecated.  When it is defined, it should point to a function
   that acts the same as the :c:member:`~PyTypeObject.tp_setattro` function, but taking a C string
   instead of a Python string object to give the attribute name.

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_setattr`, :c:member:`~PyTypeObject.tp_setattro`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_setattro`: a subtype
   inherits both :c:member:`~PyTypeObject.tp_setattr` and :c:member:`~PyTypeObject.tp_setattro` from its base type when
   the subtype's :c:member:`~PyTypeObject.tp_setattr` and :c:member:`~PyTypeObject.tp_setattro` are both ``NULL``.


.. c:member:: PyAsyncMethods* PyTypeObject.tp_as_async

   Pointer to an additional structure that contains fields relevant only to
   objects which implement :term:`awaitable` and :term:`asynchronous iterator`
   protocols at the C-level.  See :ref:`async-structs` for details.

   .. versionadded:: 3.5
      Formerly known as ``tp_compare`` and ``tp_reserved``.

   **Inheritance:**

   The :c:member:`~PyTypeObject.tp_as_async` field is not inherited,
   but the contained fields are inherited individually.


.. c:member:: reprfunc PyTypeObject.tp_repr

   .. corresponding-type-slot:: Py_tp_repr

   .. index:: pair: built-in function; repr

   An optional pointer to a function that implements the built-in function
   :func:`repr`.

   The signature is the same as for :c:func:`PyObject_Repr`::

      PyObject *tp_repr(PyObject *self);

   The function must return a string or a Unicode object.  Ideally,
   this function should return a string that, when passed to
   :func:`eval`, given a suitable environment, returns an object with the
   same value.  If this is not feasible, it should return a string starting with
   ``'<'`` and ending with ``'>'`` from which both the type and the value of the
   object can be deduced.

   **Inheritance:**

   This field is inherited by subtypes.

   **Default:**

   When this field is not set, a string of the form ``<%s object at %p>`` is
   returned, where ``%s`` is replaced by the type name, and ``%p`` by the object's
   memory address.


.. c:member:: PyNumberMethods* PyTypeObject.tp_as_number

   Pointer to an additional structure that contains fields relevant only to
   objects which implement the number protocol.  These fields are documented in
   :ref:`number-structs`.

   **Inheritance:**

   The :c:member:`~PyTypeObject.tp_as_number` field is not inherited, but the contained fields are
   inherited individually.


.. c:member:: PySequenceMethods* PyTypeObject.tp_as_sequence

   Pointer to an additional structure that contains fields relevant only to
   objects which implement the sequence protocol.  These fields are documented
   in :ref:`sequence-structs`.

   **Inheritance:**

   The :c:member:`~PyTypeObject.tp_as_sequence` field is not inherited, but the contained fields
   are inherited individually.


.. c:member:: PyMappingMethods* PyTypeObject.tp_as_mapping

   Pointer to an additional structure that contains fields relevant only to
   objects which implement the mapping protocol.  These fields are documented in
   :ref:`mapping-structs`.

   **Inheritance:**

   The :c:member:`~PyTypeObject.tp_as_mapping` field is not inherited, but the contained fields
   are inherited individually.


.. c:member:: hashfunc PyTypeObject.tp_hash

   .. corresponding-type-slot:: Py_tp_hash

   .. index:: pair: built-in function; hash

   An optional pointer to a function that implements the built-in function
   :func:`hash`.

   The signature is the same as for :c:func:`PyObject_Hash`::

      Py_hash_t tp_hash(PyObject *);

   The value ``-1`` should not be returned as a
   normal return value; when an error occurs during the computation of the hash
   value, the function should set an exception and return ``-1``.

   When this field is not set (*and* :c:member:`~PyTypeObject.tp_richcompare` is not set),
   an attempt to take the hash of the object raises :exc:`TypeError`.
   This is the same as setting it to :c:func:`PyObject_HashNotImplemented`.

   This field can be set explicitly to :c:func:`PyObject_HashNotImplemented` to
   block inheritance of the hash method from a parent type. This is interpreted
   as the equivalent of ``__hash__ = None`` at the Python level, causing
   ``isinstance(o, collections.Hashable)`` to correctly return ``False``. Note
   that the converse is also true - setting ``__hash__ = None`` on a class at
   the Python level will result in the ``tp_hash`` slot being set to
   :c:func:`PyObject_HashNotImplemented`.

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_hash`, :c:member:`~PyTypeObject.tp_richcompare`

   This field is inherited by subtypes together with
   :c:member:`~PyTypeObject.tp_richcompare`: a subtype inherits both of
   :c:member:`~PyTypeObject.tp_richcompare` and :c:member:`~PyTypeObject.tp_hash`, when the subtype's
   :c:member:`~PyTypeObject.tp_richcompare` and :c:member:`~PyTypeObject.tp_hash` are both ``NULL``.

   **Default:**

   :c:data:`PyBaseObject_Type` uses :c:func:`PyObject_GenericHash`.


.. c:member:: ternaryfunc PyTypeObject.tp_call

   .. corresponding-type-slot:: Py_tp_call

   An optional pointer to a function that implements calling the object.  This
   should be ``NULL`` if the object is not callable.  The signature is the same as
   for :c:func:`PyObject_Call`::

      PyObject *tp_call(PyObject *self, PyObject *args, PyObject *kwargs);

   **Inheritance:**

   This field is inherited by subtypes.


.. c:member:: reprfunc PyTypeObject.tp_str

   .. corresponding-type-slot:: Py_tp_str

   An optional pointer to a function that implements the built-in operation
   :func:`str`.  (Note that :class:`str` is a type now, and :func:`str` calls the
   constructor for that type.  This constructor calls :c:func:`PyObject_Str` to do
   the actual work, and :c:func:`PyObject_Str` will call this handler.)

   The signature is the same as for :c:func:`PyObject_Str`::

      PyObject *tp_str(PyObject *self);

   The function must return a string or a Unicode object.  It should be a "friendly" string
   representation of the object, as this is the representation that will be used,
   among other things, by the :func:`print` function.

   **Inheritance:**

   This field is inherited by subtypes.

   **Default:**

   When this field is not set, :c:func:`PyObject_Repr` is called to return a string
   representation.


.. c:member:: getattrofunc PyTypeObject.tp_getattro

   .. corresponding-type-slot:: Py_tp_getattro

   An optional pointer to the get-attribute function.

   The signature is the same as for :c:func:`PyObject_GetAttr`::

      PyObject *tp_getattro(PyObject *self, PyObject *attr);

   It is usually convenient to set this field to :c:func:`PyObject_GenericGetAttr`,
   which implements the normal way of looking for object attributes.

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_getattr`, :c:member:`~PyTypeObject.tp_getattro`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_getattr`: a subtype
   inherits both :c:member:`~PyTypeObject.tp_getattr` and :c:member:`~PyTypeObject.tp_getattro` from its base type when
   the subtype's :c:member:`~PyTypeObject.tp_getattr` and :c:member:`~PyTypeObject.tp_getattro` are both ``NULL``.

   **Default:**

   :c:data:`PyBaseObject_Type` uses :c:func:`PyObject_GenericGetAttr`.


.. c:member:: setattrofunc PyTypeObject.tp_setattro

   .. corresponding-type-slot:: Py_tp_setattro

   An optional pointer to the function for setting and deleting attributes.

   The signature is the same as for :c:func:`PyObject_SetAttr`::

      int tp_setattro(PyObject *self, PyObject *attr, PyObject *value);

   In addition, setting *value* to ``NULL`` to delete an attribute must be
   supported.  It is usually convenient to set this field to
   :c:func:`PyObject_GenericSetAttr`, which implements the normal
   way of setting object attributes.

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_setattr`, :c:member:`~PyTypeObject.tp_setattro`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_setattr`: a subtype
   inherits both :c:member:`~PyTypeObject.tp_setattr` and :c:member:`~PyTypeObject.tp_setattro` from its base type when
   the subtype's :c:member:`~PyTypeObject.tp_setattr` and :c:member:`~PyTypeObject.tp_setattro` are both ``NULL``.

   **Default:**

   :c:data:`PyBaseObject_Type` uses :c:func:`PyObject_GenericSetAttr`.


.. c:member:: PyBufferProcs* PyTypeObject.tp_as_buffer

   Pointer to an additional structure that contains fields relevant only to objects
   which implement the buffer interface.  These fields are documented in
   :ref:`buffer-structs`.

   **Inheritance:**

   The :c:member:`~PyTypeObject.tp_as_buffer` field is not inherited,
   but the contained fields are inherited individually.


.. c:member:: unsigned long PyTypeObject.tp_flags

   This field is a bit mask of various flags.  Some flags indicate variant
   semantics for certain situations; others are used to indicate that certain
   fields in the type object (or in the extension structures referenced via
   :c:member:`~PyTypeObject.tp_as_number`, :c:member:`~PyTypeObject.tp_as_sequence`, :c:member:`~PyTypeObject.tp_as_mapping`, and
   :c:member:`~PyTypeObject.tp_as_buffer`) that were historically not always present are valid; if
   such a flag bit is clear, the type fields it guards must not be accessed and
   must be considered to have a zero or ``NULL`` value instead.

   **Inheritance:**

   Inheritance of this field is complicated.  Most flag bits are inherited
   individually, i.e. if the base type has a flag bit set, the subtype inherits
   this flag bit.  The flag bits that pertain to extension structures are strictly
   inherited if the extension structure is inherited, i.e. the base type's value of
   the flag bit is copied into the subtype together with a pointer to the extension
   structure.  The :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit is inherited together with
   the :c:member:`~PyTypeObject.tp_traverse` and :c:member:`~PyTypeObject.tp_clear` fields, i.e. if the
   :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit is clear in the subtype and the
   :c:member:`~PyTypeObject.tp_traverse` and :c:member:`~PyTypeObject.tp_clear` fields in the subtype exist and have
   ``NULL`` values.

   .. XXX are most flag bits *really* inherited individually?

   **Default:**

   :c:data:`PyBaseObject_Type` uses
   ``Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE``.

   **Bit Masks:**

   .. c:namespace:: NULL

   The following bit masks are currently defined; these can be ORed together using
   the ``|`` operator to form the value of the :c:member:`~PyTypeObject.tp_flags` field.  The macro
   :c:func:`PyType_HasFeature` takes a type and a flags value, *tp* and *f*, and
   checks whether ``tp->tp_flags & f`` is non-zero.

   .. c:macro:: Py_TPFLAGS_HEAPTYPE

      This bit is set when the type object itself is allocated on the heap, for
      example, types created dynamically using :c:func:`PyType_FromSpec`.  In this
      case, the :c:member:`~PyObject.ob_type` field of its instances is considered a reference to
      the type, and the type object is INCREF'ed when a new instance is created, and
      DECREF'ed when an instance is destroyed (this does not apply to instances of
      subtypes; only the type referenced by the instance's ob_type gets INCREF'ed or
      DECREF'ed). Heap types should also :ref:`support garbage collection <supporting-cycle-detection>`
      as they can form a reference cycle with their own module object.

      **Inheritance:**

      ???


   .. c:macro:: Py_TPFLAGS_BASETYPE

      This bit is set when the type can be used as the base type of another type.  If
      this bit is clear, the type cannot be subtyped (similar to a "final" class in
      Java).

      **Inheritance:**

      ???


   .. c:macro:: Py_TPFLAGS_READY

      This bit is set when the type object has been fully initialized by
      :c:func:`PyType_Ready`.

      **Inheritance:**

      ???


   .. c:macro:: Py_TPFLAGS_READYING

      This bit is set while :c:func:`PyType_Ready` is in the process of initializing
      the type object.

      **Inheritance:**

      ???


   .. c:macro:: Py_TPFLAGS_HAVE_GC

      This bit is set when the object supports garbage collection.  If this bit
      is set, memory for new instances (see :c:member:`~PyTypeObject.tp_alloc`)
      must be allocated using :c:macro:`PyObject_GC_New` or
      :c:func:`PyType_GenericAlloc` and deallocated (see
      :c:member:`~PyTypeObject.tp_free`) using :c:func:`PyObject_GC_Del`.  More
      information in section :ref:`supporting-cycle-detection`.

      **Inheritance:**

      Group: :c:macro:`Py_TPFLAGS_HAVE_GC`, :c:member:`~PyTypeObject.tp_traverse`, :c:member:`~PyTypeObject.tp_clear`

      The :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit is inherited
      together with the :c:member:`~PyTypeObject.tp_traverse` and :c:member:`~PyTypeObject.tp_clear`
      fields, i.e.  if the :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit is
      clear in the subtype and the :c:member:`~PyTypeObject.tp_traverse` and
      :c:member:`~PyTypeObject.tp_clear` fields in the subtype exist and have ``NULL``
      values.


   .. c:macro:: Py_TPFLAGS_DEFAULT

      This is a bitmask of all the bits that pertain to the existence of certain
      fields in the type object and its extension structures. Currently, it includes
      the following bits: :c:macro:`Py_TPFLAGS_HAVE_STACKLESS_EXTENSION`.

      **Inheritance:**

      ???


   .. c:macro:: Py_TPFLAGS_METHOD_DESCRIPTOR

      This bit indicates that objects behave like unbound methods.

      If this flag is set for ``type(meth)``, then:

      - ``meth.__get__(obj, cls)(*args, **kwds)`` (with ``obj`` not None)
        must be equivalent to ``meth(obj, *args, **kwds)``.

      - ``meth.__get__(None, cls)(*args, **kwds)``
        must be equivalent to ``meth(*args, **kwds)``.

      This flag enables an optimization for typical method calls like
      ``obj.meth()``: it avoids creating a temporary "bound method" object for
      ``obj.meth``.

      .. versionadded:: 3.8

      **Inheritance:**

      This flag is never inherited by types without the
      :c:macro:`Py_TPFLAGS_IMMUTABLETYPE` flag set.  For extension types, it is
      inherited whenever :c:member:`~PyTypeObject.tp_descr_get` is inherited.

   .. c:macro:: Py_TPFLAGS_MANAGED_DICT

      This bit indicates that instances of the class have a :attr:`~object.__dict__`
      attribute, and that the space for the dictionary is managed by the VM.

      If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` must also be set.

      The type traverse function must call :c:func:`PyObject_VisitManagedDict`
      and its clear function must call :c:func:`PyObject_ClearManagedDict`.

      .. versionadded:: 3.12

      **Inheritance:**

      This flag is inherited unless the
      :c:member:`~PyTypeObject.tp_dictoffset` field is set in a superclass.


   .. c:macro:: Py_TPFLAGS_MANAGED_WEAKREF

      This bit indicates that instances of the class should be weakly
      referenceable.

      If this flag is set, :c:macro:`Py_TPFLAGS_HAVE_GC` must also be set.

      .. versionadded:: 3.12

      **Inheritance:**

      This flag is inherited unless the
      :c:member:`~PyTypeObject.tp_weaklistoffset` field is set in a superclass.


   .. c:macro:: Py_TPFLAGS_PREHEADER

      These bits indicate that the VM will manage some fields by storing them
      before the object. Currently, this macro is equivalent to
      :c:expr:`Py_TPFLAGS_MANAGED_DICT | Py_TPFLAGS_MANAGED_WEAKREF`.

      This macro value relies on the implementation of the VM, so its value is not
      stable and may change in a future version. Prefer using individual
      flags instead.

      .. versionadded:: 3.12


   .. c:macro:: Py_TPFLAGS_ITEMS_AT_END

      Only usable with variable-size types, i.e. ones with non-zero
      :c:member:`~PyTypeObject.tp_itemsize`.

      Indicates that the variable-sized portion of an instance of this type is
      at the end of the instance's memory area, at an offset of
      ``Py_TYPE(obj)->tp_basicsize`` (which may be different in each
      subclass).

      When setting this flag, be sure that all superclasses either
      use this memory layout, or are not variable-sized.
      Python does not check this.

      .. versionadded:: 3.12

      **Inheritance:**

      This flag is inherited.

   .. XXX Document more flags here?


   .. c:macro:: Py_TPFLAGS_LONG_SUBCLASS
   .. c:macro:: Py_TPFLAGS_LIST_SUBCLASS
   .. c:macro:: Py_TPFLAGS_TUPLE_SUBCLASS
   .. c:macro:: Py_TPFLAGS_BYTES_SUBCLASS
   .. c:macro:: Py_TPFLAGS_UNICODE_SUBCLASS
   .. c:macro:: Py_TPFLAGS_DICT_SUBCLASS
   .. c:macro:: Py_TPFLAGS_BASE_EXC_SUBCLASS
   .. c:macro:: Py_TPFLAGS_TYPE_SUBCLASS

      Functions such as :c:func:`PyLong_Check` will call :c:func:`PyType_FastSubclass`
      with one of these flags to quickly determine if a type is a subclass
      of a built-in type; such specific checks are faster than a generic
      check, like :c:func:`PyObject_IsInstance`. Custom types that inherit
      from built-ins should have their :c:member:`~PyTypeObject.tp_flags`
      set appropriately, or the code that interacts with such types
      will behave differently depending on what kind of check is used.


   .. c:macro:: Py_TPFLAGS_HAVE_FINALIZE

      This bit is set when the :c:member:`~PyTypeObject.tp_finalize` slot is present in the
      type structure.

      .. versionadded:: 3.4

      .. deprecated:: 3.8
         This flag isn't necessary anymore, as the interpreter assumes the
         :c:member:`~PyTypeObject.tp_finalize` slot is always present in the
         type structure.


   .. c:macro:: _Py_TPFLAGS_HAVE_VECTORCALL
      :no-typesetting:

   .. c:macro:: Py_TPFLAGS_HAVE_VECTORCALL

      This bit is set when the class implements
      the :ref:`vectorcall protocol <vectorcall>`.
      See :c:member:`~PyTypeObject.tp_vectorcall_offset` for details.

      **Inheritance:**

      This bit is inherited if :c:member:`~PyTypeObject.tp_call` is also
      inherited.

      .. versionadded:: 3.8 as ``_Py_TPFLAGS_HAVE_VECTORCALL``

      .. versionchanged:: 3.9

      Renamed to the current name, without the leading underscore.
      The old provisional name is :term:`soft deprecated`.

      .. versionchanged:: 3.12

         This flag is now removed from a class when the class's
         :py:meth:`~object.__call__` method is reassigned.

         This flag can now be inherited by mutable classes.

   .. c:macro:: Py_TPFLAGS_IMMUTABLETYPE

      This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.

      :c:func:`PyType_Ready` automatically applies this flag to
      :ref:`static types <static-types>`.

      **Inheritance:**

      This flag is not inherited.

      .. versionadded:: 3.10

   .. c:macro:: Py_TPFLAGS_DISALLOW_INSTANTIATION

      Disallow creating instances of the type: set
      :c:member:`~PyTypeObject.tp_new` to NULL and don't create the ``__new__``
      key in the type dictionary.

      The flag must be set before creating the type, not after. For example, it
      must be set before :c:func:`PyType_Ready` is called on the type.

      The flag is set automatically on :ref:`static types <static-types>` if
      :c:member:`~PyTypeObject.tp_base` is NULL or ``&PyBaseObject_Type`` and
      :c:member:`~PyTypeObject.tp_new` is NULL.

      **Inheritance:**

      This flag is not inherited.
      However, subclasses will not be instantiable unless they provide a
      non-NULL :c:member:`~PyTypeObject.tp_new` (which is only possible
      via the C API).

      .. note::

         To disallow instantiating a class directly but allow instantiating
         its subclasses (e.g. for an :term:`abstract base class`),
         do not use this flag.
         Instead, make :c:member:`~PyTypeObject.tp_new` only succeed for
         subclasses.

      .. versionadded:: 3.10


   .. c:macro:: Py_TPFLAGS_MAPPING

      This bit indicates that instances of the class may match mapping patterns
      when used as the subject of a :keyword:`match` block. It is automatically
      set when registering or subclassing :class:`collections.abc.Mapping`, and
      unset when registering :class:`collections.abc.Sequence`.

      .. note::

         :c:macro:`Py_TPFLAGS_MAPPING` and :c:macro:`Py_TPFLAGS_SEQUENCE` are
         mutually exclusive; it is an error to enable both flags simultaneously.

      **Inheritance:**

      This flag is inherited by types that do not already set
      :c:macro:`Py_TPFLAGS_SEQUENCE`.

      .. seealso:: :pep:`634` -- Structural Pattern Matching: Specification

      .. versionadded:: 3.10


   .. c:macro:: Py_TPFLAGS_SEQUENCE

      This bit indicates that instances of the class may match sequence patterns
      when used as the subject of a :keyword:`match` block. It is automatically
      set when registering or subclassing :class:`collections.abc.Sequence`, and
      unset when registering :class:`collections.abc.Mapping`.

      .. note::

         :c:macro:`Py_TPFLAGS_MAPPING` and :c:macro:`Py_TPFLAGS_SEQUENCE` are
         mutually exclusive; it is an error to enable both flags simultaneously.

      **Inheritance:**

      This flag is inherited by types that do not already set
      :c:macro:`Py_TPFLAGS_MAPPING`.

      .. seealso:: :pep:`634` -- Structural Pattern Matching: Specification

      .. versionadded:: 3.10


   .. c:macro:: Py_TPFLAGS_VALID_VERSION_TAG

      Internal. Do not set or unset this flag.
      To indicate that a class has changed call :c:func:`PyType_Modified`

      .. warning::
         This flag is present in header files, but is not be used.
         It will be removed in a future version of CPython


.. c:member:: const char* PyTypeObject.tp_doc

   .. corresponding-type-slot:: Py_tp_doc

   An optional pointer to a NUL-terminated C string giving the docstring for this
   type object.  This is exposed as the :attr:`~type.__doc__` attribute on the
   type and instances of the type.

   **Inheritance:**

   This field is *not* inherited by subtypes.


.. c:member:: traverseproc PyTypeObject.tp_traverse

   .. corresponding-type-slot:: Py_tp_traverse

   An optional pointer to a traversal function for the garbage collector.  This is
   only used if the :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit is set.  The signature is::

      int tp_traverse(PyObject *self, visitproc visit, void *arg);

   More information about Python's garbage collection scheme can be found
   in section :ref:`supporting-cycle-detection`.

   The :c:member:`~PyTypeObject.tp_traverse` pointer is used by the garbage collector to detect
   reference cycles. A typical implementation of a :c:member:`~PyTypeObject.tp_traverse` function
   simply calls :c:func:`Py_VISIT` on each of the instance's members that are Python
   objects that the instance owns. For example, this is function :c:func:`!local_traverse` from the
   :mod:`!_thread` extension module::

      static int
      local_traverse(PyObject *op, visitproc visit, void *arg)
      {
          localobject *self = (localobject *) op;
          Py_VISIT(self->args);
          Py_VISIT(self->kw);
          Py_VISIT(self->dict);
          return 0;
      }

   Note that :c:func:`Py_VISIT` is called only on those members that can participate
   in reference cycles.  Although there is also a ``self->key`` member, it can only
   be ``NULL`` or a Python string and therefore cannot be part of a reference cycle.

   On the other hand, even if you know a member can never be part of a cycle, as a
   debugging aid you may want to visit it anyway just so the :mod:`gc` module's
   :func:`~gc.get_referents` function will include it.

   Heap types (:c:macro:`Py_TPFLAGS_HEAPTYPE`) must visit their type with::

       Py_VISIT(Py_TYPE(self));

   It is only needed since Python 3.9. To support Python 3.8 and older, this
   line must be conditional::

       #if PY_VERSION_HEX >= 0x03090000
           Py_VISIT(Py_TYPE(self));
       #endif

   If the :c:macro:`Py_TPFLAGS_MANAGED_DICT` bit is set in the
   :c:member:`~PyTypeObject.tp_flags` field, the traverse function must call
   :c:func:`PyObject_VisitManagedDict` like this::

       PyObject_VisitManagedDict((PyObject*)self, visit, arg);

   .. warning::
       When implementing :c:member:`~PyTypeObject.tp_traverse`, only the
       members that the instance *owns* (by having :term:`strong references
       <strong reference>` to them) must be
       visited. For instance, if an object supports weak references via the
       :c:member:`~PyTypeObject.tp_weaklist` slot, the pointer supporting
       the linked list (what *tp_weaklist* points to) must **not** be
       visited as the instance does not directly own the weak references to itself
       (the weakreference list is there to support the weak reference machinery,
       but the instance has no strong reference to the elements inside it, as they
       are allowed to be removed even if the instance is still alive).

   .. warning::
      The traversal function must not have any side effects.  It must not
      modify the reference counts of any Python objects nor create or destroy
      any Python objects.

   Note that :c:func:`Py_VISIT` requires the *visit* and *arg* parameters to
   :c:func:`!local_traverse` to have these specific names; don't name them just
   anything.

   Instances of :ref:`heap-allocated types <heap-types>` hold a reference to
   their type. Their traversal function must therefore either visit
   :c:func:`Py_TYPE(self) <Py_TYPE>`, or delegate this responsibility by
   calling ``tp_traverse`` of another heap-allocated type (such as a
   heap-allocated superclass).
   If they do not, the type object may not be garbage-collected.

   .. note::

      The :c:member:`~PyTypeObject.tp_traverse` function can be called from any
      thread.

   .. versionchanged:: 3.9

      Heap-allocated types are expected to visit ``Py_TYPE(self)`` in
      ``tp_traverse``.  In earlier versions of Python, due to
      `bug 40217 <https://bugs.python.org/issue40217>`_, doing this
      may lead to crashes in subclasses.

   **Inheritance:**

   Group: :c:macro:`Py_TPFLAGS_HAVE_GC`, :c:member:`~PyTypeObject.tp_traverse`, :c:member:`~PyTypeObject.tp_clear`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_clear` and the
   :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit: the flag bit, :c:member:`~PyTypeObject.tp_traverse`, and
   :c:member:`~PyTypeObject.tp_clear` are all inherited from the base type if they are all zero in
   the subtype.


.. c:member:: inquiry PyTypeObject.tp_clear

   .. corresponding-type-slot:: Py_tp_clear

   An optional pointer to a clear function.  The signature is::

      int tp_clear(PyObject *);

   The purpose of this function is to break reference cycles that are causing a
   :term:`cyclic isolate` so that the objects can be safely destroyed.  A
   cleared object is a partially destroyed object; the object is not obligated
   to satisfy design invariants held during normal use.

   :c:member:`!tp_clear` does not need to delete references to objects that
   can't participate in reference cycles, such as Python strings or Python
   integers.  However, it may be convenient to clear all references, and write
   the type's :c:member:`~PyTypeObject.tp_dealloc` function to invoke
   :c:member:`!tp_clear` to avoid code duplication.  (Beware that
   :c:member:`!tp_clear` might have already been called. Prefer calling
   idempotent functions like :c:func:`Py_CLEAR`.)

   Any non-trivial cleanup should be performed in
   :c:member:`~PyTypeObject.tp_finalize` instead of :c:member:`!tp_clear`.

   .. note::

      If :c:member:`!tp_clear` fails to break a reference cycle then the
      objects in the :term:`cyclic isolate` may remain indefinitely
      uncollectable ("leak").  See :data:`gc.garbage`.

   .. note::

      Referents (direct and indirect) might have already been cleared; they are
      not guaranteed to be in a consistent state.

   .. note::

      The :c:member:`~PyTypeObject.tp_clear` function can be called from any
      thread.

   .. note::

      An object is not guaranteed to be automatically cleared before its
      destructor (:c:member:`~PyTypeObject.tp_dealloc`) is called.

   This function differs from the destructor
   (:c:member:`~PyTypeObject.tp_dealloc`) in the following ways:

   * The purpose of clearing an object is to remove references to other objects
     that might participate in a reference cycle.  The purpose of the
     destructor, on the other hand, is a superset: it must release *all*
     resources it owns, including references to objects that cannot participate
     in a reference cycle (e.g., integers) as well as the object's own memory
     (by calling :c:member:`~PyTypeObject.tp_free`).
   * When :c:member:`!tp_clear` is called, other objects might still hold
     references to the object being cleared.  Because of this,
     :c:member:`!tp_clear` must not deallocate the object's own memory
     (:c:member:`~PyTypeObject.tp_free`).  The destructor, on the other hand,
     is only called when no (strong) references exist, and as such, must
     safely destroy the object itself by deallocating it.
   * :c:member:`!tp_clear` might never be automatically called.  An object's
     destructor, on the other hand, will be automatically called some time
     after the object becomes unreachable (i.e., either there are no references
     to the object or the object is a member of a :term:`cyclic isolate`).

   No guarantees are made about when, if, or how often Python automatically
   clears an object, except:

   * Python will not automatically clear an object if it is reachable, i.e.,
     there is a reference to it and it is not a member of a :term:`cyclic
     isolate`.
   * Python will not automatically clear an object if it has not been
     automatically finalized (see :c:member:`~PyTypeObject.tp_finalize`).  (If
     the finalizer resurrected the object, the object may or may not be
     automatically finalized again before it is cleared.)
   * If an object is a member of a :term:`cyclic isolate`, Python will not
     automatically clear it if any member of the cyclic isolate has not yet
     been automatically finalized (:c:member:`~PyTypeObject.tp_finalize`).
   * Python will not destroy an object until after any automatic calls to its
     :c:member:`!tp_clear` function have returned.  This ensures that the act
     of breaking a reference cycle does not invalidate the ``self`` pointer
     while :c:member:`!tp_clear` is still executing.
   * Python will not automatically call :c:member:`!tp_clear` multiple times
     concurrently.

   CPython currently only automatically clears objects as needed to break
   reference cycles in a :term:`cyclic isolate`, but future versions might
   clear objects regularly before their destruction.

   Taken together, all :c:member:`~PyTypeObject.tp_clear` functions in the
   system must combine to break all reference cycles.  This is subtle, and if
   in any doubt supply a :c:member:`~PyTypeObject.tp_clear` function.  For
   example, the tuple type does not implement a
   :c:member:`~PyTypeObject.tp_clear` function, because it's possible to prove
   that no reference cycle can be composed entirely of tuples.  Therefore the
   :c:member:`~PyTypeObject.tp_clear` functions of other types are responsible
   for breaking any cycle containing a tuple.  This isn't immediately obvious,
   and there's rarely a good reason to avoid implementing
   :c:member:`~PyTypeObject.tp_clear`.

   Implementations of :c:member:`~PyTypeObject.tp_clear` should drop the instance's references to
   those of its members that may be Python objects, and set its pointers to those
   members to ``NULL``, as in the following example::

      static int
      local_clear(PyObject *op)
      {
          localobject *self = (localobject *) op;
          Py_CLEAR(self->key);
          Py_CLEAR(self->args);
          Py_CLEAR(self->kw);
          Py_CLEAR(self->dict);
          return 0;
      }

   The :c:func:`Py_CLEAR` macro should be used, because clearing references is
   delicate:  the reference to the contained object must not be released
   (via :c:func:`Py_DECREF`) until
   after the pointer to the contained object is set to ``NULL``.  This is because
   releasing the reference may cause the contained object to become trash,
   triggering a chain of reclamation activity that may include invoking arbitrary
   Python code (due to finalizers, or weakref callbacks, associated with the
   contained object). If it's possible for such code to reference *self* again,
   it's important that the pointer to the contained object be ``NULL`` at that time,
   so that *self* knows the contained object can no longer be used.  The
   :c:func:`Py_CLEAR` macro performs the operations in a safe order.

   If the :c:macro:`Py_TPFLAGS_MANAGED_DICT` bit is set in the
   :c:member:`~PyTypeObject.tp_flags` field, the clear function must call
   :c:func:`PyObject_ClearManagedDict` like this::

       PyObject_ClearManagedDict((PyObject*)self);

   More information about Python's garbage collection scheme can be found in
   section :ref:`supporting-cycle-detection`.

   **Inheritance:**

   Group: :c:macro:`Py_TPFLAGS_HAVE_GC`, :c:member:`~PyTypeObject.tp_traverse`, :c:member:`~PyTypeObject.tp_clear`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_traverse` and the
   :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit: the flag bit, :c:member:`~PyTypeObject.tp_traverse`, and
   :c:member:`~PyTypeObject.tp_clear` are all inherited from the base type if they are all zero in
   the subtype.

   .. seealso::

      :ref:`life-cycle` for details about how this slot relates to other slots.


.. c:member:: richcmpfunc PyTypeObject.tp_richcompare

   .. corresponding-type-slot:: Py_tp_richcompare

   An optional pointer to the rich comparison function, whose signature is::

      PyObject *tp_richcompare(PyObject *self, PyObject *other, int op);

   The first parameter is guaranteed to be an instance of the type
   that is defined by :c:type:`PyTypeObject`.

   The function should return the result of the comparison (usually ``Py_True``
   or ``Py_False``).  If the comparison is undefined, it must return
   ``Py_NotImplemented``, if another error occurred it must return ``NULL`` and
   set an exception condition.

   The following constants are defined to be used as the third argument for
   :c:member:`~PyTypeObject.tp_richcompare` and for :c:func:`PyObject_RichCompare`:

   .. c:namespace:: NULL

   +--------------------+------------+
   | Constant           | Comparison |
   +====================+============+
   | .. c:macro:: Py_LT | ``<``      |
   +--------------------+------------+
   | .. c:macro:: Py_LE | ``<=``     |
   +--------------------+------------+
   | .. c:macro:: Py_EQ | ``==``     |
   +--------------------+------------+
   | .. c:macro:: Py_NE | ``!=``     |
   +--------------------+------------+
   | .. c:macro:: Py_GT | ``>``      |
   +--------------------+------------+
   | .. c:macro:: Py_GE | ``>=``     |
   +--------------------+------------+

   The following macro is defined to ease writing rich comparison functions:

   .. c:macro:: Py_RETURN_RICHCOMPARE(VAL_A, VAL_B, op)

      Return ``Py_True`` or ``Py_False`` from the function, depending on the
      result of a comparison.
      VAL_A and VAL_B must be orderable by C comparison operators (for example,
      they may be C ints or floats). The third argument specifies the requested
      operation, as for :c:func:`PyObject_RichCompare`.

      The returned value is a new :term:`strong reference`.

      On error, sets an exception and returns ``NULL`` from the function.

      .. versionadded:: 3.7

   **Inheritance:**

   Group: :c:member:`~PyTypeObject.tp_hash`, :c:member:`~PyTypeObject.tp_richcompare`

   This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_hash`:
   a subtype inherits :c:member:`~PyTypeObject.tp_richcompare` and :c:member:`~PyTypeObject.tp_hash` when
   the subtype's :c:member:`~PyTypeObject.tp_richcompare` and :c:member:`~PyTypeObject.tp_hash` are both
   ``NULL``.

   **Default:**

   :c:data:`PyBaseObject_Type` provides a :c:member:`~PyTypeObject.tp_richcompare`
   implementation, which may be inherited.  However, if only
   :c:member:`~PyTypeObject.tp_hash` is defined, not even the inherited function is used
   and instances of the type will not be able to participate in any
   comparisons.


.. c:member:: Py_ssize_t PyTypeObject.tp_weaklistoffset

   While this field is still supported, :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF`
   should be used instead, if at all possible.

   If the instances of this type are weakly referenceable, this field is greater
   than zero and contains the offset in the instance structure of the weak
   reference list head (ignoring the GC header, if present); this offset is used by
   :c:func:`PyObject_ClearWeakRefs` and the ``PyWeakref_*`` functions.  The
   instance structure needs to include a field of type :c:expr:`PyObject*` which is
   initialized to ``NULL``.

   Do not confuse this field with :c:member:`~PyTypeObject.tp_weaklist`; that is the list head for
   weak references to the type object itself.

   It is an error to set both the :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF` bit and
   :c:member:`~PyTypeObject.tp_weaklistoffset`.

   **Inheritance:**

   This field is inherited by subtypes, but see the rules listed below. A subtype
   may override this offset; this means that the subtype uses a different weak
   reference list head than the base type.  Since the list head is always found via
   :c:member:`~PyTypeObject.tp_weaklistoffset`, this should not be a problem.

   **Default:**

   If the :c:macro:`Py_TPFLAGS_MANAGED_WEAKREF` bit is set in the
   :c:member:`~PyTypeObject.tp_flags` field, then
   :c:member:`~PyTypeObject.tp_weaklistoffset` will be set to a negative value,
   to indicate that it is unsafe to use this field.


.. c:member:: getiterfunc PyTypeObject.tp_iter

   .. corresponding-type-slot:: Py_tp_iter

   An optional pointer to a function that returns an :term:`iterator` for the
   object.  Its presence normally signals that the instances of this type are
   :term:`iterable` (although sequences may be iterable without this function).

   This function has the same signature as :c:func:`PyObject_GetIter`::

      PyObject *tp_iter(PyObject *self);

   **Inheritance:**

   This field is inherited by subtypes.


.. c:member:: iternextfunc PyTypeObject.tp_iternext

   .. corresponding-type-slot:: Py_tp_iternext

   An optional pointer to a function that returns the next item in an
   :term:`iterator`. The signature is::

      PyObject *tp_iternext(PyObject *self);

   When the iterator is exhausted, it must return ``NULL``; a :exc:`StopIteration`
   exception may or may not be set.  When another error occurs, it must return
   ``NULL`` too.  Its presence signals that the instances of this type are
   iterators.

   Iterator types should also define the :c:member:`~PyTypeObject.tp_iter` function, and that
   function should return the iterator instance itself (not a new iterator
   instance).

   This function has the same signature as :c:func:`PyIter_Next`.

   **Inheritance:**

   This field is inherited by subtypes.


.. c:member:: struct PyMethodDef* PyTypeObject.tp_methods

   .. corresponding-type-slot:: Py_tp_methods

   An optional pointer to a static ``NULL``-terminated array of :c:type:`PyMethodDef`
   structures, declaring regular methods of this type.

   For each entry in the array, an entry is added to the type's dictionary (see
   :c:member:`~PyTypeObject.tp_dict` below) containing a method descriptor.

   **Inheritance:**

   This field is not inherited by subtypes (methods are inherited through a
   different mechanism).


.. c:member:: struct PyMemberDef* PyTypeObject.tp_members

   .. corresponding-type-slot:: Py_tp_members

   An optional pointer to a static ``NULL``-terminated array of :c:type:`PyMemberDef`
   structures, declaring regular data members (fields or slots) of instances of
   this type.

   For each entry in the array, an entry is added to the type's dictionary (see
   :c:member:`~PyTypeObject.tp_dict` below) containing a member descriptor.

   **Inheritance:**

   This field is not inherited by subtypes (members are inherited through a
   different mechanism).


.. c:member:: struct PyGetSetDef* PyTypeObject.tp_getset

   .. corresponding-type-slot:: Py_tp_getset

   An optional pointer to a static ``NULL``-terminated array of :c:type:`PyGetSetDef`
   structures, declaring computed attributes of instances of this type.

   For each entry in the array, an entry is added to the type's dictionary (see
   :c:member:`~PyTypeObject.tp_dict` below) containing a getset descriptor.

   **Inheritance:**

   This field is not inherited by subtypes (computed attributes are inherited
   through a different mechanism).


.. c:member:: PyTypeObject* PyTypeObject.tp_base

   .. corresponding-type-slot:: Py_tp_base

   An optional pointer to a base type from which type properties are inherited.  At
   this level, only single inheritance is supported; multiple inheritance require
   dynamically creating a type object by calling the metatype.

   .. note::

       .. from Modules/xxmodule.c

       Slot initialization is subject to the rules of initializing globals.
       C99 requires the initializers to be "address constants".  Function
       designators like :c:func:`PyType_GenericNew`, with implicit conversion
       to a pointer, are valid C99 address constants.

       However, the unary '&' operator applied to a non-static variable
       like :c:data:`PyBaseObject_Type` is not required to produce an address
       constant.  Compilers may support this (gcc does), MSVC does not.
       Both compilers are strictly standard conforming in this particular
       behavior.

       Consequently, :c:member:`~PyTypeObject.tp_base` should be set in
       the extension module's init function.

   **Inheritance:**

   This field is not inherited by subtypes (obviously).

   **Default:**

   This field defaults to ``&PyBaseObject_Type`` (which to Python
   programmers is known as the type :class:`object`).


.. c:member:: PyObject* PyTypeObject.tp_dict

   The type's dictionary is stored here by :c:func:`PyType_Ready`.

   This field should normally be initialized to ``NULL`` before PyType_Ready is
   called; it may also be initialized to a dictionary containing initial attributes
   for the type.  Once :c:func:`PyType_Ready` has initialized the type, extra
   attributes for the type may be added to this dictionary only if they don't
   correspond to overloaded operations (like :meth:`~object.__add__`).  Once
   initialization for the type has finished, this field should be
   treated as read-only.

   Some types may not store their dictionary in this slot.
   Use :c:func:`PyType_GetDict` to retrieve the dictionary for an arbitrary
   type.

   .. versionchanged:: 3.12

      Internals detail: For static builtin types, this is always ``NULL``.
      Instead, the dict for such types is stored on ``PyInterpreterState``.
      Use :c:func:`PyType_GetDict` to get the dict for an arbitrary type.

   **Inheritance:**

   This field is not inherited by subtypes (though the attributes defined in here
   are inherited through a different mechanism).

   **Default:**

   If this field is ``NULL``, :c:func:`PyType_Ready` will assign a new
   dictionary to it.

   .. warning::

      It is not safe to use :c:func:`PyDict_SetItem` on or otherwise modify
      :c:member:`~PyTypeObject.tp_dict` with the dictionary C-API.


.. c:member:: descrgetfunc PyTypeObject.tp_descr_get

   .. corresponding-type-slot:: Py_tp_descr_get

   An optional pointer to a "descriptor get" function.

   The function signature is::

      PyObject * tp_descr_get(PyObject *self, PyObject *obj, PyObject *type);

   .. XXX explain more?

   **Inheritance:**

   This field is inherited by subtypes.


.. c:member:: descrsetfunc PyTypeObject.tp_descr_set

   .. corresponding-type-slot:: Py_tp_descr_set

   An optional pointer to a function for setting and deleting
   a descriptor's value.

   The function signature is::

      int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);

   The *value* argument is set to ``NULL`` to delete the value.

   .. XXX explain more?

   **Inheritance:**

   This field is inherited by subtypes.


.. c:member:: Py_ssize_t PyTypeObject.tp_dictoffset

   While this field is still supported, :c:macro:`Py_TPFLAGS_MANAGED_DICT` should be
   used instead, if at all possible.

   If the instances of this type have a dictionary containing instance variables,
   this field is non-zero and contains the offset in the instances of the type of
   the instance variable dictionary; this offset is used by
   :c:func:`PyObject_GenericGetAttr`.

   Do not confuse this field with :c:member:`~PyTypeObject.tp_dict`; that is the dictionary for
   attributes of the type object itself.

   The value specifies the offset of the dictionary from the start of the instance structure.

   The :c:member:`~PyTypeObject.tp_dictoffset` should be regarded as write-only.
   To get the pointer to the dictionary call :c:func:`PyObject_GenericGetDict`.
   Calling :c:func:`PyObject_GenericGetDict` may need to allocate memory for the
   dictionary, so it is may be more efficient to call :c:func:`PyObject_GetAttr`
   when accessing an attribute on the object.

   It is an error to set both the :c:macro:`Py_TPFLAGS_MANAGED_DICT` bit and
   :c:member:`~PyTypeObject.tp_dictoffset`.

   **Inheritance:**

   This field is inherited by subtypes. A subtype should not override this offset;
   doing so could be unsafe, if C code tries to access the dictionary at the
   previous offset.
   To properly support inheritance, use :c:macro:`Py_TPFLAGS_MANAGED_DICT`.

   **Default:**

   This slot has no default.  For :ref:`static types <static-types>`, if the
   field is ``NULL`` then no :attr:`~object.__dict__` gets created for instances.

   If the :c:macro:`Py_TPFLAGS_MANAGED_DICT` bit is set in the
   :c:member:`~PyTypeObject.tp_flags` field, then
   :c:member:`~PyTypeObject.tp_dictoffset` will be set to ``-1``, to indicate
   that it is unsafe to use this field.


.. c:member:: initproc PyTypeObject.tp_init

   .. corresponding-type-slot:: Py_tp_init

   An optional pointer to an instance initialization function.

   This function corresponds to the :meth:`~object.__init__` method of classes.  Like
   :meth:`!__init__`, it is possible to create an instance without calling
   :meth:`!__init__`, and it is possible to reinitialize an instance by calling its
   :meth:`!__init__` method again.

   The function signature is::

      int tp_init(PyObject *self, PyObject *args, PyObject *kwds);

   The self argument is the instance to be initialized; the *args* and *kwds*
   arguments represent positional and keyword arguments of the call to
   :meth:`~object.__init__`.

   The :c:member:`~PyTypeObject.tp_init` function, if not ``NULL``, is called when an instance is
   created normally by calling its type, after the type's :c:member:`~PyTypeObject.tp_new` function
   has returned an instance of the type.  If the :c:member:`~PyTypeObject.tp_new` function returns an
   instance of some other type that is not a subtype of the original type, no
   :c:member:`~PyTypeObject.tp_init` function is called; if :c:member:`~PyTypeObject.tp_new` returns an instance of a
   subtype of the original type, the subtype's :c:member:`~PyTypeObject.tp_init` is called.

   Returns ``0`` on success, ``-1`` and sets an exception on error.

   **Inheritance:**

   This field is inherited by subtypes.

   **Default:**

   For :ref:`static types <static-types>` this field does not have a default.


.. c:member:: allocfunc PyTypeObject.tp_alloc

   .. corresponding-type-slot:: Py_tp_alloc

   An optional pointer to an instance allocation function.

   The function signature is::

      PyObject *tp_alloc(PyTypeObject *self, Py_ssize_t nitems);

   **Inheritance:**

   Static subtypes inherit this slot, which will be
   :c:func:`PyType_GenericAlloc` if inherited from :class:`object`.

   :ref:`Heap subtypes <heap-types>` do not inherit this slot.

   **Default:**

   For heap subtypes, this field is always set to
   :c:func:`PyType_GenericAlloc`.

   For static subtypes, this slot is inherited (see above).


.. c:member:: newfunc PyTypeObject.tp_new

   .. corresponding-type-slot:: Py_tp_new

   An optional pointer to an instance creation function.

   The function signature is::

      PyObject *tp_new(PyTypeObject *subtype, PyObject *args, PyObject *kwds);

   The *subtype* argument is the type of the object being created; the *args* and
   *kwds* arguments represent positional and keyword arguments of the call to the
   type.  Note that *subtype* doesn't have to equal the type whose :c:member:`~PyTypeObject.tp_new`
   function is called; it may be a subtype of that type (but not an unrelated
   type).

   The :c:member:`~PyTypeObject.tp_new` function should call ``subtype->tp_alloc(subtype, nitems)``
   to allocate space for the object, and then do only as much further
   initialization as is absolutely necessary.  Initialization that can safely be
   ignored or repeated should be placed in the :c:member:`~PyTypeObject.tp_init` handler.  A good
   rule of thumb is that for immutable types, all initialization should take place
   in :c:member:`~PyTypeObject.tp_new`, while for mutable types, most initialization should be
   deferred to :c:member:`~PyTypeObject.tp_init`.

   Set the :c:macro:`Py_TPFLAGS_DISALLOW_INSTANTIATION` flag to disallow creating
   instances of the type in Python.

   **Inheritance:**

   This field is inherited by subtypes, except it is not inherited by
   :ref:`static types <static-types>` whose :c:member:`~PyTypeObject.tp_base`
   is ``NULL`` or ``&PyBaseObject_Type``.

   **Default:**

   For :ref:`static types <static-types>` this field has no default.
   This means if the slot is defined as ``NULL``, the type cannot be called
   to create new instances; presumably there is some other way to create
   instances, like a factory function.


.. c:member:: freefunc PyTypeObject.tp_free

   .. corresponding-type-slot:: Py_tp_free

   An optional pointer to an instance deallocation function.  Its signature is::

      void tp_free(void *self);

   This function must free the memory allocated by
   :c:member:`~PyTypeObject.tp_alloc`.

   **Inheritance:**

   Static subtypes inherit this slot, which will be :c:func:`PyObject_Free` if
   inherited from :class:`object`.  Exception: If the type supports garbage
   collection (i.e., the :c:macro:`Py_TPFLAGS_HAVE_GC` flag is set in
   :c:member:`~PyTypeObject.tp_flags`) and it would inherit
   :c:func:`PyObject_Free`, then this slot is not inherited but instead defaults
   to :c:func:`PyObject_GC_Del`.

   :ref:`Heap subtypes <heap-types>` do not inherit this slot.

   **Default:**

   For :ref:`heap subtypes <heap-types>`, this slot defaults to a deallocator suitable to match
   :c:func:`PyType_GenericAlloc` and the value of the
   :c:macro:`Py_TPFLAGS_HAVE_GC` flag.

   For static subtypes, this slot is inherited (see above).


.. c:member:: inquiry PyTypeObject.tp_is_gc

   .. corresponding-type-slot:: Py_tp_is_gc

   An optional pointer to a function called by the garbage collector.

   The garbage collector needs to know whether a particular object is collectible
   or not.  Normally, it is sufficient to look at the object's type's
   :c:member:`~PyTypeObject.tp_flags` field, and check the :c:macro:`Py_TPFLAGS_HAVE_GC` flag bit.  But
   some types have a mixture of statically and dynamically allocated instances, and
   the statically allocated instances are not collectible.  Such types should
   define this function; it should return ``1`` for a collectible instance, and
   ``0`` for a non-collectible instance. The signature is::

      int tp_is_gc(PyObject *self);

   (The only example of this are types themselves.  The metatype,
   :c:data:`PyType_Type`, defines this function to distinguish between statically
   and :ref:`dynamically allocated types <heap-types>`.)

   **Inheritance:**

   This field is inherited by subtypes.

   **Default:**

   This slot has no default.  If this field is ``NULL``,
   :c:macro:`Py_TPFLAGS_HAVE_GC` is used as the functional equivalent.


.. c:member:: PyObject* PyTypeObject.tp_bases

   .. corresponding-type-slot:: Py_tp_bases

   Tuple of base types.

   This field should be set to ``NULL`` and treated as read-only.
   Python will fill it in when the type is :c:func:`initialized <PyType_Ready>`.

   For dynamically created classes, the :c:data:`Py_tp_bases`
   :c:type:`slot <PyType_Slot>` can be used instead of the *bases* argument
   of :c:func:`PyType_FromSpecWithBases`.
   The argument form is preferred.

   .. warning::

      Multiple inheritance does not work well for statically defined types.
      If you set ``tp_bases`` to a tuple, Python will not raise an error,
      but some slots will only be inherited from the first base.

   **Inheritance:**

   This field is not inherited.


.. c:member:: PyObject* PyTypeObject.tp_mro

   Tuple containing the expanded set of base types, starting with the type itself
   and ending with :class:`object`, in Method Resolution Order.

   This field should be set to ``NULL`` and treated as read-only.
   Python will fill it in when the type is :c:func:`initialized <PyType_Ready>`.

   **Inheritance:**

   This field is not inherited; it is calculated fresh by
   :c:func:`PyType_Ready`.


.. c:member:: PyObject* PyTypeObject.tp_cache

   Unused.  Internal use only.

   **Inheritance:**

   This field is not inherited.


.. c:member:: void* PyTypeObject.tp_subclasses

   A collection of subclasses.  Internal use only.  May be an invalid pointer.

   To get a list of subclasses, call the Python method
   :py:meth:`~type.__subclasses__`.

   .. versionchanged:: 3.12

      For some types, this field does not hold a valid :c:expr:`PyObject*`.
      The type was changed to :c:expr:`void*` to indicate this.

   **Inheritance:**

   This field is not inherited.


.. c:member:: PyObject* PyTypeObject.tp_weaklist

   Weak reference list head, for weak references to this type object.  Not
   inherited.  Internal use only.

   .. versionchanged:: 3.12

      Internals detail: For the static builtin types this is always ``NULL``,
      even if weakrefs are added.  Instead, the weakrefs for each are stored
      on ``PyInterpreterState``.  Use the public C-API or the internal
      ``_PyObject_GET_WEAKREFS_LISTPTR()`` macro to avoid the distinction.

   **Inheritance:**

   This field is not inherited.


.. c:member:: destructor PyTypeObject.tp_del

   .. corresponding-type-slot:: Py_tp_del

   This field is deprecated.  Use :c:member:`~PyTypeObject.tp_finalize` instead.


.. c:member:: unsigned int PyTypeObject.tp_version_tag

   Used to index into the method cache.  Internal use only.

   **Inheritance:**

   This field is not inherited.


.. c:member:: destructor PyTypeObject.tp_finalize

   .. corresponding-type-slot:: Py_tp_finalize

   An optional pointer to an instance finalization function.  This is the C
   implementation of the :meth:`~object.__del__` special method.  Its signature
   is::

      void tp_finalize(PyObject *self);

   The primary purpose of finalization is to perform any non-trivial cleanup
   that must be performed before the object is destroyed, while the object and
   any other objects it directly or indirectly references are still in a
   consistent state.  The finalizer is allowed to execute
   arbitrary Python code.

   Before Python automatically finalizes an object, some of the object's direct
   or indirect referents might have themselves been automatically finalized.
   However, none of the referents will have been automatically cleared
   (:c:member:`~PyTypeObject.tp_clear`) yet.

   Other non-finalized objects might still be using a finalized object, so the
   finalizer must leave the object in a sane state (e.g., invariants are still
   met).

   .. note::

      After Python automatically finalizes an object, Python might start
      automatically clearing (:c:member:`~PyTypeObject.tp_clear`) the object
      and its referents (direct and indirect).  Cleared objects are not
      guaranteed to be in a consistent state; a finalized object must be able
      to tolerate cleared referents.

   .. note::

      An object is not guaranteed to be automatically finalized before its
      destructor (:c:member:`~PyTypeObject.tp_dealloc`) is called.  It is
      recommended to call :c:func:`PyObject_CallFinalizerFromDealloc` at the
      beginning of :c:member:`!tp_dealloc` to guarantee that the object is
      always finalized before destruction.

   .. note::

      The :c:member:`~PyTypeObject.tp_finalize` function can be called from any
      thread, although the :term:`GIL` will be held.

   .. note::

      The :c:member:`!tp_finalize` function can be called during shutdown,
      after some global variables have been deleted.  See the documentation of
      the :meth:`~object.__del__` method for details.

   When Python finalizes an object, it behaves like the following algorithm:

   #. Python might mark the object as *finalized*.  Currently, Python always
      marks objects whose type supports garbage collection (i.e., the
      :c:macro:`Py_TPFLAGS_HAVE_GC` flag is set in
      :c:member:`~PyTypeObject.tp_flags`) and never marks other types of
      objects; this might change in a future version.
   #. If the object is not marked as *finalized* and its
      :c:member:`!tp_finalize` finalizer function is non-``NULL``, the
      finalizer function is called.
   #. If the finalizer function was called and the finalizer made the object
      reachable (i.e., there is a reference to the object and it is not a
      member of a :term:`cyclic isolate`), then the finalizer is said to have
      *resurrected* the object.  It is unspecified whether the finalizer can
      also resurrect the object by adding a new reference to the object that
      does not make it reachable, i.e., the object is (still) a member of a
      cyclic isolate.
   #. If the finalizer resurrected the object, the object's pending destruction
      is canceled and the object's *finalized* mark might be removed if
      present.  Currently, Python never removes the *finalized* mark; this
      might change in a future version.

   *Automatic finalization* refers to any finalization performed by Python
   except via calls to :c:func:`PyObject_CallFinalizer` or
   :c:func:`PyObject_CallFinalizerFromDealloc`.  No guarantees are made about
   when, if, or how often an object is automatically finalized, except:

   * Python will not automatically finalize an object if it is reachable, i.e.,
     there is a reference to it and it is not a member of a :term:`cyclic
     isolate`.
   * Python will not automatically finalize an object if finalizing it would
     not mark the object as *finalized*.  Currently, this applies to objects
     whose type does not support garbage collection, i.e., the
     :c:macro:`Py_TPFLAGS_HAVE_GC` flag is not set.  Such objects can still be
     manually finalized by calling :c:func:`PyObject_CallFinalizer` or
     :c:func:`PyObject_CallFinalizerFromDealloc`.
   * Python will not automatically finalize any two members of a :term:`cyclic
     isolate` concurrently.
   * Python will not automatically finalize an object after it has
     automatically cleared (:c:member:`~PyTypeObject.tp_clear`) the object.
   * If an object is a member of a :term:`cyclic isolate`, Python will not
     automatically finalize it after automatically clearing (see
     :c:member:`~PyTypeObject.tp_clear`) any other member.
   * Python will automatically finalize every member of a :term:`cyclic
     isolate` before it automatically clears (see
     :c:member:`~PyTypeObject.tp_clear`) any of them.
   * If Python is going to automatically clear an object
     (:c:member:`~PyTypeObject.tp_clear`), it will automatically finalize the
     object first.

   Python currently only automatically finalizes objects that are members of a
   :term:`cyclic isolate`, but future versions might finalize objects regularly
   before their destruction.

   To manually finalize an object, do not call this function directly; call
   :c:func:`PyObject_CallFinalizer` or
   :c:func:`PyObject_CallFinalizerFromDealloc` instead.

   :c:member:`~PyTypeObject.tp_finalize` should leave the current exception
   status unchanged.  The recommended way to write a non-trivial finalizer is
   to back up the exception at the beginning by calling
   :c:func:`PyErr_GetRaisedException` and restore the exception at the end by
   calling :c:func:`PyErr_SetRaisedException`.  If an exception is encountered
   in the middle of the finalizer, log and clear it with
   :c:func:`PyErr_WriteUnraisable` or :c:func:`PyErr_FormatUnraisable`.  For
   example::

      static void
      foo_finalize(PyObject *self)
      {
          // Save the current exception, if any.
          PyObject *exc = PyErr_GetRaisedException();

          // ...

          if (do_something_that_might_raise() != success_indicator) {
              PyErr_WriteUnraisable(self);
              goto done;
          }

      done:
          // Restore the saved exception.  This silently discards any exception
          // raised above, so be sure to call PyErr_WriteUnraisable first if
          // necessary.
          PyErr_SetRaisedException(exc);
      }

   **Inheritance:**

   This field is inherited by subtypes.

   .. versionadded:: 3.4

   .. versionchanged:: 3.8

      Before version 3.8 it was necessary to set the
      :c:macro:`Py_TPFLAGS_HAVE_FINALIZE` flags bit in order for this field to be
      used.  This is no longer required.

   .. seealso::

      * :pep:`442`: "Safe object finalization"
      * :ref:`life-cycle` for details about how this slot relates to other
        slots.
      * :c:func:`PyObject_CallFinalizer`
      * :c:func:`PyObject_CallFinalizerFromDealloc`


.. c:member:: vectorcallfunc PyTypeObject.tp_vectorcall

   .. corresponding-type-slot:: Py_tp_vectorcall

   A :ref:`vectorcall function <vectorcall>` to use for calls of this type
   object (rather than instances).
   In other words, ``tp_vectorcall`` can be used to optimize ``type.__call__``,
   which typically returns a new instance of *type*.

   As with any vectorcall function, if ``tp_vectorcall`` is ``NULL``,
   the *tp_call* protocol (``Py_TYPE(type)->tp_call``) is used instead.

   .. note::

      The :ref:`vectorcall protocol <vectorcall>` requires that the vectorcall
      function has the same behavior as the corresponding ``tp_call``.
      This means that ``type->tp_vectorcall`` must match the behavior of
      ``Py_TYPE(type)->tp_call``.

      Specifically, if *type* uses the default metaclass,
      ``type->tp_vectorcall`` must behave the same as
      :c:expr:`PyType_Type->tp_call`, which:

      - calls ``type->tp_new``,

      - if the result is a subclass of *type*, calls ``type->tp_init``
        on the result of ``tp_new``, and

      - returns the result of ``tp_new``.

      Typically, ``tp_vectorcall`` is overridden to optimize this process
      for specific :c:member:`~PyTypeObject.tp_new` and
      :c:member:`~PyTypeObject.tp_init`.
      When doing this for user-subclassable types, note that both can be
      overridden (using :py:func:`~object.__new__` and
      :py:func:`~object.__init__`, respectively).



   **Inheritance:**

   This field is never inherited.

   .. versionadded:: 3.9 (the field exists since 3.8 but it's only used since 3.9)


.. c:member:: unsigned char PyTypeObject.tp_watched

   Internal. Do not use.

   .. versionadded:: 3.12


.. _static-types:

Static Types
------------

Traditionally, types defined in C code are *static*, that is,
a static :c:type:`PyTypeObject` structure is defined directly in code
and initialized using :c:func:`PyType_Ready`.

This results in types that are limited relative to types defined in Python:

* Static types are limited to one base, i.e. they cannot use multiple
  inheritance.
* Static type objects (but not necessarily their instances) are immutable.
  It is not possible to add or modify the type object's attributes from Python.
* Static type objects are shared across
  :ref:`sub-interpreters <sub-interpreter-support>`, so they should not
  include any subinterpreter-specific state.

Also, since :c:type:`PyTypeObject` is only part of the :ref:`Limited API
<limited-c-api>` as an opaque struct, any extension modules using static types must be
compiled for a specific Python minor version.


.. _heap-types:

Heap Types
----------

An alternative to :ref:`static types <static-types>` is *heap-allocated types*,
or *heap types* for short, which correspond closely to classes created by
Python's ``class`` statement. Heap types have the :c:macro:`Py_TPFLAGS_HEAPTYPE`
flag set.

This is done by filling a :c:type:`PyType_Spec` structure and calling
:c:func:`PyType_FromSpec`, :c:func:`PyType_FromSpecWithBases`,
:c:func:`PyType_FromModuleAndSpec`, or :c:func:`PyType_FromMetaclass`.


.. _number-structs:

Number Object Structures
------------------------

.. sectionauthor:: Amaury Forgeot d'Arc


.. c:type:: PyNumberMethods

   This structure holds pointers to the functions which an object uses to
   implement the number protocol.  Each function is used by the function of
   similar name documented in the :ref:`number` section.

   .. XXX Drop the definition?

   Here is the structure definition::

       typedef struct {
            binaryfunc nb_add;
            binaryfunc nb_subtract;
            binaryfunc nb_multiply;
            binaryfunc nb_remainder;
            binaryfunc nb_divmod;
            ternaryfunc nb_power;
            unaryfunc nb_negative;
            unaryfunc nb_positive;
            unaryfunc nb_absolute;
            inquiry nb_bool;
            unaryfunc nb_invert;
            binaryfunc nb_lshift;
            binaryfunc nb_rshift;
            binaryfunc nb_and;
            binaryfunc nb_xor;
            binaryfunc nb_or;
            unaryfunc nb_int;
            void *nb_reserved;
            unaryfunc nb_float;

            binaryfunc nb_inplace_add;
            binaryfunc nb_inplace_subtract;
            binaryfunc nb_inplace_multiply;
            binaryfunc nb_inplace_remainder;
            ternaryfunc nb_inplace_power;
            binaryfunc nb_inplace_lshift;
            binaryfunc nb_inplace_rshift;
            binaryfunc nb_inplace_and;
            binaryfunc nb_inplace_xor;
            binaryfunc nb_inplace_or;

            binaryfunc nb_floor_divide;
            binaryfunc nb_true_divide;
            binaryfunc nb_inplace_floor_divide;
            binaryfunc nb_inplace_true_divide;

            unaryfunc nb_index;

            binaryfunc nb_matrix_multiply;
            binaryfunc nb_inplace_matrix_multiply;
       } PyNumberMethods;

   .. note::

      Binary and ternary functions must check the type of all their operands,
      and implement the necessary conversions (at least one of the operands is
      an instance of the defined type).  If the operation is not defined for the
      given operands, binary and ternary functions must return
      ``Py_NotImplemented``, if another error occurred they must return ``NULL``
      and set an exception.

   .. note::

      The :c:member:`~PyNumberMethods.nb_reserved` field should always be ``NULL``.  It
      was previously called :c:member:`!nb_long`, and was renamed in
      Python 3.0.1.

.. c:member:: binaryfunc PyNumberMethods.nb_add

   .. corresponding-type-slot:: Py_nb_add

.. c:member:: binaryfunc PyNumberMethods.nb_subtract

   .. corresponding-type-slot:: Py_nb_subtract

.. c:member:: binaryfunc PyNumberMethods.nb_multiply

   .. corresponding-type-slot:: Py_nb_multiply

.. c:member:: binaryfunc PyNumberMethods.nb_remainder

   .. corresponding-type-slot:: Py_nb_remainder

.. c:member:: binaryfunc PyNumberMethods.nb_divmod

   .. corresponding-type-slot:: Py_nb_divmod

.. c:member:: ternaryfunc PyNumberMethods.nb_power

   .. corresponding-type-slot:: Py_nb_power

.. c:member:: unaryfunc PyNumberMethods.nb_negative

   .. corresponding-type-slot:: Py_nb_negative

.. c:member:: unaryfunc PyNumberMethods.nb_positive

   .. corresponding-type-slot:: Py_nb_positive

.. c:member:: unaryfunc PyNumberMethods.nb_absolute

   .. corresponding-type-slot:: Py_nb_absolute

.. c:member:: inquiry PyNumberMethods.nb_bool

   .. corresponding-type-slot:: Py_nb_bool

.. c:member:: unaryfunc PyNumberMethods.nb_invert

   .. corresponding-type-slot:: Py_nb_invert

.. c:member:: binaryfunc PyNumberMethods.nb_lshift

   .. corresponding-type-slot:: Py_nb_lshift

.. c:member:: binaryfunc PyNumberMethods.nb_rshift

   .. corresponding-type-slot:: Py_nb_rshift

.. c:member:: binaryfunc PyNumberMethods.nb_and

   .. corresponding-type-slot:: Py_nb_and

.. c:member:: binaryfunc PyNumberMethods.nb_xor

   .. corresponding-type-slot:: Py_nb_xor

.. c:member:: binaryfunc PyNumberMethods.nb_or

   .. corresponding-type-slot:: Py_nb_or

.. c:member:: unaryfunc PyNumberMethods.nb_int

   .. corresponding-type-slot:: Py_nb_int

.. c:member:: void *PyNumberMethods.nb_reserved

.. c:member:: unaryfunc PyNumberMethods.nb_float

   .. corresponding-type-slot:: Py_nb_float

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_add

   .. corresponding-type-slot:: Py_nb_inplace_add

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_subtract

   .. corresponding-type-slot:: Py_nb_inplace_subtract

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_multiply

   .. corresponding-type-slot:: Py_nb_inplace_multiply

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_remainder

   .. corresponding-type-slot:: Py_nb_inplace_remainder

.. c:member:: ternaryfunc PyNumberMethods.nb_inplace_power

   .. corresponding-type-slot:: Py_nb_inplace_power

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_lshift

   .. corresponding-type-slot:: Py_nb_inplace_lshift

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_rshift

   .. corresponding-type-slot:: Py_nb_inplace_rshift

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_and

   .. corresponding-type-slot:: Py_nb_inplace_and

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_xor

   .. corresponding-type-slot:: Py_nb_inplace_xor

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_or

   .. corresponding-type-slot:: Py_nb_inplace_or

.. c:member:: binaryfunc PyNumberMethods.nb_floor_divide

   .. corresponding-type-slot:: Py_nb_floor_divide

.. c:member:: binaryfunc PyNumberMethods.nb_true_divide

   .. corresponding-type-slot:: Py_nb_true_divide

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_floor_divide

   .. corresponding-type-slot:: Py_nb_inplace_floor_divide

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_true_divide

   .. corresponding-type-slot:: Py_nb_inplace_true_divide

.. c:member:: unaryfunc PyNumberMethods.nb_index

   .. corresponding-type-slot:: Py_nb_index

.. c:member:: binaryfunc PyNumberMethods.nb_matrix_multiply

   .. corresponding-type-slot:: Py_nb_matrix_multiply

.. c:member:: binaryfunc PyNumberMethods.nb_inplace_matrix_multiply

   .. corresponding-type-slot:: Py_nb_inplace_matrix_multiply



.. _mapping-structs:

Mapping Object Structures
-------------------------

.. sectionauthor:: Amaury Forgeot d'Arc


.. c:type:: PyMappingMethods

   This structure holds pointers to the functions which an object uses to
   implement the mapping protocol.  It has three members:

.. c:member:: lenfunc PyMappingMethods.mp_length

   .. corresponding-type-slot:: Py_mp_length

   This function is used by :c:func:`PyMapping_Size` and
   :c:func:`PyObject_Size`, and has the same signature.  This slot may be set to
   ``NULL`` if the object has no defined length.

.. c:member:: binaryfunc PyMappingMethods.mp_subscript

   .. corresponding-type-slot:: Py_mp_subscript

   This function is used by :c:func:`PyObject_GetItem` and
   :c:func:`PySequence_GetSlice`, and has the same signature as
   :c:func:`!PyObject_GetItem`.  This slot must be filled for the
   :c:func:`PyMapping_Check` function to return ``1``, it can be ``NULL``
   otherwise.

.. c:member:: objobjargproc PyMappingMethods.mp_ass_subscript

   .. corresponding-type-slot:: Py_mp_ass_subscript

   This function is used by :c:func:`PyObject_SetItem`,
   :c:func:`PyObject_DelItem`, :c:func:`PySequence_SetSlice` and
   :c:func:`PySequence_DelSlice`.  It has the same signature as
   :c:func:`!PyObject_SetItem`, but *v* can also be set to ``NULL`` to delete
   an item.  If this slot is ``NULL``, the object does not support item
   assignment and deletion.


.. _sequence-structs:

Sequence Object Structures
--------------------------

.. sectionauthor:: Amaury Forgeot d'Arc


.. c:type:: PySequenceMethods

   This structure holds pointers to the functions which an object uses to
   implement the sequence protocol.

.. c:member:: lenfunc PySequenceMethods.sq_length

   .. corresponding-type-slot:: Py_sq_length

   This function is used by :c:func:`PySequence_Size` and
   :c:func:`PyObject_Size`, and has the same signature.  It is also used for
   handling negative indices via the :c:member:`~PySequenceMethods.sq_item`
   and the :c:member:`~PySequenceMethods.sq_ass_item` slots.

.. c:member:: binaryfunc PySequenceMethods.sq_concat

   .. corresponding-type-slot:: Py_sq_concat

   This function is used by :c:func:`PySequence_Concat` and has the same
   signature.  It is also used by the ``+`` operator, after trying the numeric
   addition via the :c:member:`~PyNumberMethods.nb_add` slot.

.. c:member:: ssizeargfunc PySequenceMethods.sq_repeat

   .. corresponding-type-slot:: Py_sq_repeat

   This function is used by :c:func:`PySequence_Repeat` and has the same
   signature.  It is also used by the ``*`` operator, after trying numeric
   multiplication via the :c:member:`~PyNumberMethods.nb_multiply` slot.

.. c:member:: ssizeargfunc PySequenceMethods.sq_item

   .. corresponding-type-slot:: Py_sq_item

   This function is used by :c:func:`PySequence_GetItem` and has the same
   signature.  It is also used by :c:func:`PyObject_GetItem`, after trying
   the subscription via the :c:member:`~PyMappingMethods.mp_subscript` slot.
   This slot must be filled for the :c:func:`PySequence_Check`
   function to return ``1``, it can be ``NULL`` otherwise.

   Negative indexes are handled as follows: if the :c:member:`~PySequenceMethods.sq_length` slot is
   filled, it is called and the sequence length is used to compute a positive
   index which is passed to  :c:member:`~PySequenceMethods.sq_item`.  If :c:member:`!sq_length` is ``NULL``,
   the index is passed as is to the function.

.. c:member:: ssizeobjargproc PySequenceMethods.sq_ass_item

   .. corresponding-type-slot:: Py_sq_ass_item

   This function is used by :c:func:`PySequence_SetItem` and has the same
   signature.  It is also used by :c:func:`PyObject_SetItem` and
   :c:func:`PyObject_DelItem`, after trying the item assignment and deletion
   via the :c:member:`~PyMappingMethods.mp_ass_subscript` slot.
   This slot may be left to ``NULL`` if the object does not support
   item assignment and deletion.

.. c:member:: objobjproc PySequenceMethods.sq_contains

   .. corresponding-type-slot:: Py_sq_contains

   This function may be used by :c:func:`PySequence_Contains` and has the same
   signature.  This slot may be left to ``NULL``, in this case
   :c:func:`!PySequence_Contains` simply traverses the sequence until it
   finds a match.

.. c:member:: binaryfunc PySequenceMethods.sq_inplace_concat

   .. corresponding-type-slot:: Py_sq_inplace_concat

   This function is used by :c:func:`PySequence_InPlaceConcat` and has the same
   signature.  It should modify its first operand, and return it.  This slot
   may be left to ``NULL``, in this case :c:func:`!PySequence_InPlaceConcat`
   will fall back to :c:func:`PySequence_Concat`.  It is also used by the
   augmented assignment ``+=``, after trying numeric in-place addition
   via the :c:member:`~PyNumberMethods.nb_inplace_add` slot.

.. c:member:: ssizeargfunc PySequenceMethods.sq_inplace_repeat

   .. corresponding-type-slot:: Py_sq_inplace_repeat

   This function is used by :c:func:`PySequence_InPlaceRepeat` and has the same
   signature.  It should modify its first operand, and return it.  This slot
   may be left to ``NULL``, in this case :c:func:`!PySequence_InPlaceRepeat`
   will fall back to :c:func:`PySequence_Repeat`.  It is also used by the
   augmented assignment ``*=``, after trying numeric in-place multiplication
   via the :c:member:`~PyNumberMethods.nb_inplace_multiply` slot.


.. _buffer-structs:

Buffer Object Structures
------------------------

.. sectionauthor:: Greg J. Stein <greg@lyra.org>
.. sectionauthor:: Benjamin Peterson
.. sectionauthor:: Stefan Krah

.. c:type:: PyBufferProcs

   This structure holds pointers to the functions required by the
   :ref:`Buffer protocol <bufferobjects>`. The protocol defines how
   an exporter object can expose its internal data to consumer objects.

.. c:member:: getbufferproc PyBufferProcs.bf_getbuffer

   .. corresponding-type-slot:: Py_bf_getbuffer

   The signature of this function is::

       int (PyObject *exporter, Py_buffer *view, int flags);

   Handle a request to *exporter* to fill in *view* as specified by *flags*.
   Except for point (3), an implementation of this function MUST take these
   steps:

   (1) Check if the request can be met. If not, raise :exc:`BufferError`,
       set :c:expr:`view->obj` to ``NULL`` and return ``-1``.

   (2) Fill in the requested fields.

   (3) Increment an internal counter for the number of exports.

   (4) Set :c:expr:`view->obj` to *exporter* and increment :c:expr:`view->obj`.

   (5) Return ``0``.

   **Thread safety:**

   In :term:`free-threaded <free threading>` Python, implementations must ensure:

   * The export counter increment in step (3) must be atomic (e.g., using
     :c:func:`_Py_atomic_add_ssize` or equivalent).

   * The underlying buffer data must remain valid and at a stable memory
     location until all exports are released.

   * For objects that support resizing or reallocation (like :class:`bytearray`),
     the export counter must be checked atomically before performing such
     operations, and :exc:`BufferError` must be raised if exports exist.

   * The function must be safe to call concurrently from multiple threads.

   If *exporter* is part of a chain or tree of buffer providers, two main
   schemes can be used:

   * Re-export: Each member of the tree acts as the exporting object and
     sets :c:expr:`view->obj` to a new reference to itself.

   * Redirect: The buffer request is redirected to the root object of the
     tree. Here, :c:expr:`view->obj` will be a new reference to the root
     object.

   The individual fields of *view* are described in section
   :ref:`Buffer structure <buffer-structure>`, the rules how an exporter
   must react to specific requests are in section
   :ref:`Buffer request types <buffer-request-types>`.

   All memory pointed to in the :c:type:`Py_buffer` structure belongs to
   the exporter and must remain valid until there are no consumers left.
   :c:member:`~Py_buffer.format`, :c:member:`~Py_buffer.shape`,
   :c:member:`~Py_buffer.strides`, :c:member:`~Py_buffer.suboffsets`
   and :c:member:`~Py_buffer.internal`
   are read-only for the consumer.

   :c:func:`PyBuffer_FillInfo` provides an easy way of exposing a simple
   bytes buffer while dealing correctly with all request types.

   :c:func:`PyObject_GetBuffer` is the interface for the consumer that
   wraps this function.

.. c:member:: releasebufferproc PyBufferProcs.bf_releasebuffer

   .. corresponding-type-slot:: Py_bf_releasebuffer

   The signature of this function is::

       void (PyObject *exporter, Py_buffer *view);

   Handle a request to release the resources of the buffer. If no resources
   need to be released, :c:member:`PyBufferProcs.bf_releasebuffer` may be
   ``NULL``. Otherwise, a standard implementation of this function will take
   these optional steps:

   (1) Decrement an internal counter for the number of exports.

   (2) If the counter is ``0``, free all memory associated with *view*.

   **Thread safety:**

   In :term:`free-threaded <free threading>` Python:

   * The export counter decrement in step (1) must be atomic.

   * Any resource cleanup performed when the counter reaches zero must be
     thread-safe, as multiple threads may release buffers concurrently.

   The exporter MUST use the :c:member:`~Py_buffer.internal` field to keep
   track of buffer-specific resources. This field is guaranteed to remain
   constant, while a consumer MAY pass a copy of the original buffer as the
   *view* argument.


   This function MUST NOT decrement :c:expr:`view->obj`, since that is
   done automatically in :c:func:`PyBuffer_Release` (this scheme is
   useful for breaking reference cycles).


   :c:func:`PyBuffer_Release` is the interface for the consumer that
   wraps this function.


.. _async-structs:


Async Object Structures
-----------------------

.. sectionauthor:: Yury Selivanov <yselivanov@sprymix.com>

.. versionadded:: 3.5

.. c:type:: PyAsyncMethods

   This structure holds pointers to the functions required to implement
   :term:`awaitable` and :term:`asynchronous iterator` objects.

   Here is the structure definition::

        typedef struct {
            unaryfunc am_await;
            unaryfunc am_aiter;
            unaryfunc am_anext;
            sendfunc am_send;
        } PyAsyncMethods;

.. c:member:: unaryfunc PyAsyncMethods.am_await

   .. corresponding-type-slot:: Py_am_await

   The signature of this function is::

      PyObject *am_await(PyObject *self);

   The returned object must be an :term:`iterator`, i.e. :c:func:`PyIter_Check`
   must return ``1`` for it.

   This slot may be set to ``NULL`` if an object is not an :term:`awaitable`.

.. c:member:: unaryfunc PyAsyncMethods.am_aiter

   .. corresponding-type-slot:: Py_am_aiter

   The signature of this function is::

      PyObject *am_aiter(PyObject *self);

   Must return an :term:`asynchronous iterator` object.
   See :meth:`~object.__anext__` for details.

   This slot may be set to ``NULL`` if an object does not implement
   asynchronous iteration protocol.

.. c:member:: unaryfunc PyAsyncMethods.am_anext

   .. corresponding-type-slot:: Py_am_anext

   The signature of this function is::

      PyObject *am_anext(PyObject *self);

   Must return an :term:`awaitable` object.
   See :meth:`~object.__anext__` for details.
   This slot may be set to ``NULL``.

.. c:member:: sendfunc PyAsyncMethods.am_send

   .. corresponding-type-slot:: Py_am_send

   The signature of this function is::

      PySendResult am_send(PyObject *self, PyObject *arg, PyObject **result);

   See :c:func:`PyIter_Send` for details.
   This slot may be set to ``NULL``.

   .. versionadded:: 3.10


.. _slot-typedefs:

Slot Type typedefs
------------------

.. c:type:: PyObject *(*allocfunc)(PyTypeObject *cls, Py_ssize_t nitems)

   The purpose of this function is to separate memory allocation from memory
   initialization.  It should return a pointer to a block of memory of adequate
   length for the instance, suitably aligned, and initialized to zeros, but with
   :c:member:`~PyObject.ob_refcnt` set to ``1`` and :c:member:`~PyObject.ob_type` set to the type argument.  If
   the type's :c:member:`~PyTypeObject.tp_itemsize` is non-zero, the object's :c:member:`~PyVarObject.ob_size` field
   should be initialized to *nitems* and the length of the allocated memory block
   should be ``tp_basicsize + nitems*tp_itemsize``, rounded up to a multiple of
   ``sizeof(void*)``; otherwise, *nitems* is not used and the length of the block
   should be :c:member:`~PyTypeObject.tp_basicsize`.

   This function should not do any other instance initialization, not even to
   allocate additional memory; that should be done by :c:member:`~PyTypeObject.tp_new`.

.. c:type:: void (*destructor)(PyObject *)

.. c:type:: void (*freefunc)(void *)

   See :c:member:`~PyTypeObject.tp_free`.

.. c:type:: PyObject *(*newfunc)(PyTypeObject *, PyObject *, PyObject *)

   See :c:member:`~PyTypeObject.tp_new`.

.. c:type:: int (*initproc)(PyObject *, PyObject *, PyObject *)

   See :c:member:`~PyTypeObject.tp_init`.

.. c:type:: PyObject *(*reprfunc)(PyObject *)

   See :c:member:`~PyTypeObject.tp_repr`.

.. c:type:: PyObject *(*getattrfunc)(PyObject *self, char *attr)

   Return the value of the named attribute for the object.

.. c:type:: int (*setattrfunc)(PyObject *self, char *attr, PyObject *value)

   Set the value of the named attribute for the object.
   The value argument is set to ``NULL`` to delete the attribute.

.. c:type:: PyObject *(*getattrofunc)(PyObject *self, PyObject *attr)

   Return the value of the named attribute for the object.

   See :c:member:`~PyTypeObject.tp_getattro`.

.. c:type:: int (*setattrofunc)(PyObject *self, PyObject *attr, PyObject *value)

   Set the value of the named attribute for the object.
   The value argument is set to ``NULL`` to delete the attribute.

   See :c:member:`~PyTypeObject.tp_setattro`.

.. c:type:: PyObject *(*descrgetfunc)(PyObject *, PyObject *, PyObject *)

   See :c:member:`~PyTypeObject.tp_descr_get`.

.. c:type:: int (*descrsetfunc)(PyObject *, PyObject *, PyObject *)

   See :c:member:`~PyTypeObject.tp_descr_set`.

.. c:type:: Py_hash_t (*hashfunc)(PyObject *)

   See :c:member:`~PyTypeObject.tp_hash`.

.. c:type:: PyObject *(*richcmpfunc)(PyObject *, PyObject *, int)

   See :c:member:`~PyTypeObject.tp_richcompare`.

.. c:type:: PyObject *(*getiterfunc)(PyObject *)

   See :c:member:`~PyTypeObject.tp_iter`.

.. c:type:: PyObject *(*iternextfunc)(PyObject *)

   See :c:member:`~PyTypeObject.tp_iternext`.

.. c:type:: Py_ssize_t (*lenfunc)(PyObject *)

.. c:type:: int (*getbufferproc)(PyObject *, Py_buffer *, int)

.. c:type:: void (*releasebufferproc)(PyObject *, Py_buffer *)

.. c:type:: PyObject *(*unaryfunc)(PyObject *)

.. c:type:: PyObject *(*binaryfunc)(PyObject *, PyObject *)

.. c:type:: PySendResult (*sendfunc)(PyObject *, PyObject *, PyObject **)

   See :c:member:`~PyAsyncMethods.am_send`.

.. c:type:: PyObject *(*ternaryfunc)(PyObject *, PyObject *, PyObject *)

.. c:type:: PyObject *(*ssizeargfunc)(PyObject *, Py_ssize_t)

.. c:type:: int (*ssizeobjargproc)(PyObject *, Py_ssize_t, PyObject *)

.. c:type:: int (*objobjproc)(PyObject *, PyObject *)

.. c:type:: int (*objobjargproc)(PyObject *, PyObject *, PyObject *)


.. _typedef-examples:

Examples
--------

The following are simple examples of Python type definitions.  They
include common usage you may encounter.  Some demonstrate tricky corner
cases.  For more examples, practical info, and a tutorial, see
:ref:`defining-new-types` and :ref:`new-types-topics`.

A basic :ref:`static type <static-types>`::

   typedef struct {
       PyObject_HEAD
       const char *data;
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject),
       .tp_doc = PyDoc_STR("My objects"),
       .tp_new = myobj_new,
       .tp_dealloc = (destructor)myobj_dealloc,
       .tp_repr = (reprfunc)myobj_repr,
   };

You may also find older code (especially in the CPython code base)
with a more verbose initializer::

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       "mymod.MyObject",               /* tp_name */
       sizeof(MyObject),               /* tp_basicsize */
       0,                              /* tp_itemsize */
       (destructor)myobj_dealloc,      /* tp_dealloc */
       0,                              /* tp_vectorcall_offset */
       0,                              /* tp_getattr */
       0,                              /* tp_setattr */
       0,                              /* tp_as_async */
       (reprfunc)myobj_repr,           /* tp_repr */
       0,                              /* tp_as_number */
       0,                              /* tp_as_sequence */
       0,                              /* tp_as_mapping */
       0,                              /* tp_hash */
       0,                              /* tp_call */
       0,                              /* tp_str */
       0,                              /* tp_getattro */
       0,                              /* tp_setattro */
       0,                              /* tp_as_buffer */
       0,                              /* tp_flags */
       PyDoc_STR("My objects"),        /* tp_doc */
       0,                              /* tp_traverse */
       0,                              /* tp_clear */
       0,                              /* tp_richcompare */
       0,                              /* tp_weaklistoffset */
       0,                              /* tp_iter */
       0,                              /* tp_iternext */
       0,                              /* tp_methods */
       0,                              /* tp_members */
       0,                              /* tp_getset */
       0,                              /* tp_base */
       0,                              /* tp_dict */
       0,                              /* tp_descr_get */
       0,                              /* tp_descr_set */
       0,                              /* tp_dictoffset */
       0,                              /* tp_init */
       0,                              /* tp_alloc */
       myobj_new,                      /* tp_new */
   };

A type that supports weakrefs, instance dicts, and hashing::

   typedef struct {
       PyObject_HEAD
       const char *data;
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject),
       .tp_doc = PyDoc_STR("My objects"),
       .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
            Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_MANAGED_DICT |
            Py_TPFLAGS_MANAGED_WEAKREF,
       .tp_new = myobj_new,
       .tp_traverse = (traverseproc)myobj_traverse,
       .tp_clear = (inquiry)myobj_clear,
       .tp_alloc = PyType_GenericNew,
       .tp_dealloc = (destructor)myobj_dealloc,
       .tp_repr = (reprfunc)myobj_repr,
       .tp_hash = (hashfunc)myobj_hash,
       .tp_richcompare = PyBaseObject_Type.tp_richcompare,
   };

A str subclass that cannot be subclassed and cannot be called
to create instances (e.g. uses a separate factory func) using
:c:macro:`Py_TPFLAGS_DISALLOW_INSTANTIATION` flag::

   typedef struct {
       PyUnicodeObject raw;
       char *extra;
   } MyStr;

   static PyTypeObject MyStr_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyStr",
       .tp_basicsize = sizeof(MyStr),
       .tp_base = NULL,  // set to &PyUnicode_Type in module init
       .tp_doc = PyDoc_STR("my custom str"),
       .tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
       .tp_repr = (reprfunc)myobj_repr,
   };

The simplest :ref:`static type <static-types>` with fixed-length instances::

   typedef struct {
       PyObject_HEAD
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
   };

The simplest :ref:`static type <static-types>` with variable-length instances::

   typedef struct {
       PyObject_VAR_HEAD
       const char *data[1];
   } MyObject;

   static PyTypeObject MyObject_Type = {
       PyVarObject_HEAD_INIT(NULL, 0)
       .tp_name = "mymod.MyObject",
       .tp_basicsize = sizeof(MyObject) - sizeof(char *),
       .tp_itemsize = sizeof(char *),
   };