.. highlight:: c
.. _typeobjects:
Type Objects
------------
.. index:: object: type
.. c:type:: PyTypeObject
The C structure of the objects used to describe built-in types.
.. c:var:: PyTypeObject PyType_Type
This is the type object for type objects; it is the same object as
:class:`type` in the Python layer.
.. c:function:: int PyType_Check(PyObject *o)
Return non-zero if the object *o* is a type object, including instances of
types derived from the standard type object. Return 0 in all other cases.
This function always succeeds.
.. c:function:: int PyType_CheckExact(PyObject *o)
Return non-zero if the object *o* is a type object, but not a subtype of
the standard type object. Return 0 in all other cases. This function
always succeeds.
.. c:function:: unsigned int PyType_ClearCache()
Clear the internal lookup cache. Return the current version tag.
.. c:function:: unsigned long PyType_GetFlags(PyTypeObject* type)
Return the :c:member:`~PyTypeObject.tp_flags` member of *type*. This function is primarily
meant for use with ``Py_LIMITED_API``; the individual flag bits are
guaranteed to be stable across Python releases, but access to
:c:member:`~PyTypeObject.tp_flags` itself is not part of the limited API.
.. versionadded:: 3.2
.. versionchanged:: 3.4
The return type is now ``unsigned long`` rather than ``long``.
.. c:function:: void PyType_Modified(PyTypeObject *type)
Invalidate the internal lookup cache for the type and all of its
subtypes. This function must be called after any manual
modification of the attributes or base classes of the type.
.. c:function:: int PyType_HasFeature(PyTypeObject *o, int feature)
Return non-zero if the type object *o* sets the feature *feature*.
Type features are denoted by single bit flags.
.. c:function:: int PyType_IS_GC(PyTypeObject *o)
Return true if the type object includes support for the cycle detector; this
tests the type flag :const:`Py_TPFLAGS_HAVE_GC`.
.. c:function:: int PyType_IsSubtype(PyTypeObject *a, PyTypeObject *b)
Return true if *a* is a subtype of *b*.
This function only checks for actual subtypes, which means that
:meth:`~class.__subclasscheck__` is not called on *b*. Call
:c:func:`PyObject_IsSubclass` to do the same check that :func:`issubclass`
would do.
.. c:function:: PyObject* PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
Generic handler for the :c:member:`~PyTypeObject.tp_alloc` slot of a type object. Use
Python's default memory allocation mechanism to allocate a new instance and
initialize all its contents to ``NULL``.
.. c:function:: PyObject* PyType_GenericNew(PyTypeObject *type, PyObject *args, PyObject *kwds)
Generic handler for the :c:member:`~PyTypeObject.tp_new` slot of a type object. Create a
new instance using the type's :c:member:`~PyTypeObject.tp_alloc` slot.
.. c:function:: int PyType_Ready(PyTypeObject *type)
Finalize a type object. This should be called on all type objects to finish
their initialization. This function is responsible for adding inherited slots
from a type's base class. Return ``0`` on success, or return ``-1`` and sets an
exception on error.
.. note::
If some of the base classes implements the GC protocol and the provided
type does not include the :const:`Py_TPFLAGS_HAVE_GC` in its flags, then
the GC protocol will be automatically implemented from its parents. On
the contrary, if the type being created does include
:const:`Py_TPFLAGS_HAVE_GC` in its flags then it **must** implement the
GC protocol itself by at least implementing the
:c:member:`~PyTypeObject.tp_traverse` handle.
.. c:function:: PyObject* PyType_GetName(PyTypeObject *type)
Return the type's name. Equivalent to getting the type's ``__name__`` attribute.
.. versionadded:: 3.11
.. c:function:: PyObject* PyType_GetQualName(PyTypeObject *type)
Return the type's qualified name. Equivalent to getting the
type's ``__qualname__`` attribute.
.. versionadded:: 3.11
.. c:function:: void* PyType_GetSlot(PyTypeObject *type, int slot)
Return the function pointer stored in the given slot. If the
result is ``NULL``, this indicates that either the slot is ``NULL``,
or that the function was called with invalid parameters.
Callers will typically cast the result pointer into the appropriate
function type.
See :c:member:`PyType_Slot.slot` for possible values of the *slot* argument.
.. versionadded:: 3.4
.. versionchanged:: 3.10
:c:func:`PyType_GetSlot` can now accept all types.
Previously, it was limited to :ref:`heap types <heap-types>`.
.. c:function:: PyObject* PyType_GetModule(PyTypeObject *type)
Return the module object associated with the given type when the type was
created using :c:func:`PyType_FromModuleAndSpec`.
If no module is associated with the given type, sets :py:class:`TypeError`
and returns ``NULL``.
This function is usually used to get the module in which a method is defined.
Note that in such a method, ``PyType_GetModule(Py_TYPE(self))``
may not return the intended result.
``Py_TYPE(self)`` may be a *subclass* of the intended class, and subclasses
are not necessarily defined in the same module as their superclass.
See :c:type:`PyCMethod` to get the class that defines the method.
See :c:func:`PyType_GetModuleByDef` for cases when ``PyCMethod`` cannot
be used.
.. versionadded:: 3.9
.. c:function:: void* PyType_GetModuleState(PyTypeObject *type)
Return the state of the module object associated with the given type.
This is a shortcut for calling :c:func:`PyModule_GetState()` on the result
of :c:func:`PyType_GetModule`.
If no module is associated with the given type, sets :py:class:`TypeError`
and returns ``NULL``.
If the *type* has an associated module but its state is ``NULL``,
returns ``NULL`` without setting an exception.
.. versionadded:: 3.9
.. c:function:: PyObject* PyType_GetModuleByDef(PyTypeObject *type, struct PyModuleDef *def)
Find the first superclass whose module was created from
the given :c:type:`PyModuleDef` *def*, and return that module.
If no module is found, raises a :py:class:`TypeError` and returns ``NULL``.
This function is intended to be used together with
:c:func:`PyModule_GetState()` to get module state from slot methods (such as
:c:member:`~PyTypeObject.tp_init` or :c:member:`~PyNumberMethods.nb_add`)
and other places where a method's defining class cannot be passed using the
:c:type:`PyCMethod` calling convention.
.. versionadded:: 3.11
Creating Heap-Allocated Types
.............................
The following functions and structs are used to create
:ref:`heap types <heap-types>`.
.. c:function:: PyObject* PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
Creates and returns a :ref:`heap type <heap-types>` from the *spec*
(:const:`Py_TPFLAGS_HEAPTYPE`).
The *bases* argument can be used to specify base classes; it can either
be only one class or a tuple of classes.
If *bases* is ``NULL``, the *Py_tp_bases* slot is used instead.
If that also is ``NULL``, the *Py_tp_base* slot is used instead.
If that also is ``NULL``, the new type derives from :class:`object`.
The *module* argument can be used to record the module in which the new
class is defined. It must be a module object or ``NULL``.
If not ``NULL``, the module is associated with the new type and can later be
retrieved with :c:func:`PyType_GetModule`.
The associated module is not inherited by subclasses; it must be specified
for each class individually.
This function calls :c:func:`PyType_Ready` on the new type.
.. versionadded:: 3.9
.. versionchanged:: 3.10
The function now accepts a single class as the *bases* argument and
``NULL`` as the ``tp_doc`` slot.
.. c:function:: PyObject* PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
Equivalent to ``PyType_FromModuleAndSpec(NULL, spec, bases)``.
.. versionadded:: 3.3
.. c:function:: PyObject* PyType_FromSpec(PyType_Spec *spec)
Equivalent to ``PyType_FromSpecWithBases(spec, NULL)``.
.. c:type:: PyType_Spec
Structure defining a type's behavior.
.. c:member:: const char* PyType_Spec.name
Name of the type, used to set :c:member:`PyTypeObject.tp_name`.
.. c:member:: int PyType_Spec.basicsize
.. c:member:: int PyType_Spec.itemsize
Size of the instance in bytes, used to set
:c:member:`PyTypeObject.tp_basicsize` and
:c:member:`PyTypeObject.tp_itemsize`.
.. c:member:: int PyType_Spec.flags
Type flags, used to set :c:member:`PyTypeObject.tp_flags`.
If the ``Py_TPFLAGS_HEAPTYPE`` flag is not set,
:c:func:`PyType_FromSpecWithBases` sets it automatically.
.. c:member:: PyType_Slot *PyType_Spec.slots
Array of :c:type:`PyType_Slot` structures.
Terminated by the special slot value ``{0, NULL}``.
.. c:type:: PyType_Slot
Structure defining optional functionality of a type, containing a slot ID
and a value pointer.
.. c:member:: int PyType_Slot.slot
A slot ID.
Slot IDs are named like the field names of the structures
:c:type:`PyTypeObject`, :c:type:`PyNumberMethods`,
:c:type:`PySequenceMethods`, :c:type:`PyMappingMethods` and
:c:type:`PyAsyncMethods` with an added ``Py_`` prefix.
For example, use:
* ``Py_tp_dealloc`` to set :c:member:`PyTypeObject.tp_dealloc`
* ``Py_nb_add`` to set :c:member:`PyNumberMethods.nb_add`
* ``Py_sq_length`` to set :c:member:`PySequenceMethods.sq_length`
The following fields cannot be set at all using :c:type:`PyType_Spec` and
:c:type:`PyType_Slot`:
* :c:member:`~PyTypeObject.tp_dict`
* :c:member:`~PyTypeObject.tp_mro`
* :c:member:`~PyTypeObject.tp_cache`
* :c:member:`~PyTypeObject.tp_subclasses`
* :c:member:`~PyTypeObject.tp_weaklist`
* :c:member:`~PyTypeObject.tp_vectorcall`
* :c:member:`~PyTypeObject.tp_weaklistoffset`
(see :ref:`PyMemberDef <pymemberdef-offsets>`)
* :c:member:`~PyTypeObject.tp_dictoffset`
(see :ref:`PyMemberDef <pymemberdef-offsets>`)
* :c:member:`~PyTypeObject.tp_vectorcall_offset`
(see :ref:`PyMemberDef <pymemberdef-offsets>`)
Setting :c:data:`Py_tp_bases` or :c:data:`Py_tp_base` may be
problematic on some platforms.
To avoid issues, use the *bases* argument of
:py:func:`PyType_FromSpecWithBases` instead.
.. versionchanged:: 3.9
Slots in :c:type:`PyBufferProcs` may be set in the unlimited API.
.. versionchanged:: 3.11
:c:member:`~PyBufferProcs.bf_getbuffer` and
:c:member:`~PyBufferProcs.bf_releasebuffer` are now available
under the limited API.
.. c:member:: void *PyType_Slot.pfunc
The desired value of the slot. In most cases, this is a pointer
to a function.
Slots other than ``Py_tp_doc`` may not be ``NULL``.
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