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.. 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:: PyObject* 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 true if the object *o* is a type object, including instances of types
derived from the standard type object. Return false in all other cases.
.. c:function:: int PyType_CheckExact(PyObject *o)
Return true if the object *o* is a type object, but not a subtype of the
standard type object. Return false in all other cases.
.. 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 true 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.
.. 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.
An exception is raised if *type* is not a heap type.
.. versionadded:: 3.4
Creating Heap-Allocated Types
.............................
The following functions and structs are used to create
:ref:`heap types <heap-types>`.
.. c:function:: PyObject* PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
Creates and returns a heap type object from the *spec*.
If *bases* is a tuple, the created heap type contains all types contained
in it as base types.
If *bases* is *NULL*, the *Py_tp_base* slot is used instead.
If that also is *NULL*, the new type derives from :class:`object`.
This function calls :c:func:`PyType_Ready` on the new type.
.. 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 using *PyType_Spec* and *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_print`
* :c:member:`~PyTypeObject.tp_weaklistoffset`
* :c:member:`~PyTypeObject.tp_dictoffset`
* :c:member:`~PyBufferProcs.bf_getbuffer`
* :c:member:`~PyBufferProcs.bf_releasebuffer`
Setting :c:data:`Py_tp_bases` may be problematic on some platforms.
To avoid issues, use the *bases* argument of
:py:func:`PyType_FromSpecWithBases` instead.
.. c:member:: void *PyType_Slot.pfunc
The desired value of the slot. In most cases, this is a pointer
to a function.
May not be *NULL*.
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