Type Objects

type PyTypeObject
Part of the Limited API (as an opaque struct).

The C structure of the objects used to describe built-in types.

PyTypeObject PyType_Type
Part of the Stable ABI.

This is the type object for type objects; it is the same object as type in the Python layer.

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.

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.

unsigned int PyType_ClearCache()
Part of the Stable ABI.

Clear the internal lookup cache. Return the current version tag.

unsigned long PyType_GetFlags(PyTypeObject *type)
Part of the Stable ABI.

Return the 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 tp_flags itself is not part of the limited API.

Added in version 3.2.

Changed in version 3.4: The return type is now unsigned long rather than long.

PyObject *PyType_GetDict(PyTypeObject *type)

Return the type object’s internal namespace, which is otherwise only exposed via a read-only proxy (cls.__dict__). This is a replacement for accessing tp_dict directly. The returned dictionary must be treated as read-only.

This function is meant for specific embedding and language-binding cases, where direct access to the dict is necessary and indirect access (e.g. via the proxy or PyObject_GetAttr()) isn’t adequate.

Extension modules should continue to use tp_dict, directly or indirectly, when setting up their own types.

Added in version 3.12.

void PyType_Modified(PyTypeObject *type)
Part of the Stable ABI.

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.

int PyType_AddWatcher(PyType_WatchCallback callback)

Register callback as a type watcher. Return a non-negative integer ID which must be passed to future calls to PyType_Watch(). In case of error (e.g. no more watcher IDs available), return -1 and set an exception.

Added in version 3.12.

int PyType_ClearWatcher(int watcher_id)

Clear watcher identified by watcher_id (previously returned from PyType_AddWatcher()). Return 0 on success, -1 on error (e.g. if watcher_id was never registered.)

An extension should never call PyType_ClearWatcher with a watcher_id that was not returned to it by a previous call to PyType_AddWatcher().

Added in version 3.12.

int PyType_Watch(int watcher_id, PyObject *type)

Mark type as watched. The callback granted watcher_id by PyType_AddWatcher() will be called whenever PyType_Modified() reports a change to type. (The callback may be called only once for a series of consecutive modifications to type, if _PyType_Lookup() is not called on type between the modifications; this is an implementation detail and subject to change.)

An extension should never call PyType_Watch with a watcher_id that was not returned to it by a previous call to PyType_AddWatcher().

Added in version 3.12.

typedef int (*PyType_WatchCallback)(PyObject *type)

Type of a type-watcher callback function.

The callback must not modify type or cause PyType_Modified() to be called on type or any type in its MRO; violating this rule could cause infinite recursion.

Added in version 3.12.

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.

int PyType_IS_GC(PyTypeObject *o)

Return true if the type object includes support for the cycle detector; this tests the type flag Py_TPFLAGS_HAVE_GC.

int PyType_IsSubtype(PyTypeObject *a, PyTypeObject *b)
Part of the Stable ABI.

Return true if a is a subtype of b.

This function only checks for actual subtypes, which means that __subclasscheck__() is not called on b. Call PyObject_IsSubclass() to do the same check that issubclass() would do.

PyObject *PyType_GenericAlloc(PyTypeObject *type, Py_ssize_t nitems)
Return value: New reference. Part of the Stable ABI.

Generic handler for the 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.

PyObject *PyType_GenericNew(PyTypeObject *type, PyObject *args, PyObject *kwds)
Return value: New reference. Part of the Stable ABI.

Generic handler for the tp_new slot of a type object. Create a new instance using the type’s tp_alloc slot.

int PyType_Ready(PyTypeObject *type)
Part of the Stable ABI.

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 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 Py_TPFLAGS_HAVE_GC in its flags then it must implement the GC protocol itself by at least implementing the tp_traverse handle.

PyObject *PyType_GetName(PyTypeObject *type)
Return value: New reference. Part of the Stable ABI since version 3.11.

Return the type’s name. Equivalent to getting the type’s __name__ attribute.

Added in version 3.11.

PyObject *PyType_GetQualName(PyTypeObject *type)
Return value: New reference. Part of the Stable ABI since version 3.11.

Return the type’s qualified name. Equivalent to getting the type’s __qualname__ attribute.

Added in version 3.11.

void *PyType_GetSlot(PyTypeObject *type, int slot)
Part of the Stable ABI since version 3.4.

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 PyType_Slot.slot for possible values of the slot argument.

Added in version 3.4.

Changed in version 3.10: PyType_GetSlot() can now accept all types. Previously, it was limited to heap types.

PyObject *PyType_GetModule(PyTypeObject *type)
Part of the Stable ABI since version 3.10.

Return the module object associated with the given type when the type was created using PyType_FromModuleAndSpec().

If no module is associated with the given type, sets 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 PyCMethod to get the class that defines the method. See PyType_GetModuleByDef() for cases when PyCMethod cannot be used.

Added in version 3.9.

void *PyType_GetModuleState(PyTypeObject *type)
Part of the Stable ABI since version 3.10.

Return the state of the module object associated with the given type. This is a shortcut for calling PyModule_GetState() on the result of PyType_GetModule().

If no module is associated with the given type, sets TypeError and returns NULL.

If the type has an associated module but its state is NULL, returns NULL without setting an exception.

Added in version 3.9.

PyObject *PyType_GetModuleByDef(PyTypeObject *type, struct PyModuleDef *def)

Find the first superclass whose module was created from the given PyModuleDef def, and return that module.

If no module is found, raises a TypeError and returns NULL.

This function is intended to be used together with PyModule_GetState() to get module state from slot methods (such as tp_init or nb_add) and other places where a method’s defining class cannot be passed using the PyCMethod calling convention.

Added in version 3.11.

int PyUnstable_Type_AssignVersionTag(PyTypeObject *type)
This is Unstable API. It may change without warning in minor releases.

Attempt to assign a version tag to the given type.

Returns 1 if the type already had a valid version tag or a new one was assigned, or 0 if a new tag could not be assigned.

Added in version 3.12.

Creating Heap-Allocated Types

The following functions and structs are used to create heap types.

PyObject *PyType_FromMetaclass(PyTypeObject *metaclass, PyObject *module, PyType_Spec *spec, PyObject *bases)
Part of the Stable ABI since version 3.12.

Create and return a heap type from the spec (see Py_TPFLAGS_HEAPTYPE).

The metaclass metaclass is used to construct the resulting type object. When metaclass is NULL, the metaclass is derived from bases (or Py_tp_base[s] slots if bases is NULL, see below).

Metaclasses that override tp_new are not supported, except if tp_new is NULL. (For backwards compatibility, other PyType_From* functions allow such metaclasses. They ignore tp_new, which may result in incomplete initialization. This is deprecated and in Python 3.14+ such metaclasses will not be supported.)

The bases argument can be used to specify base classes; it can either be only one class or a tuple of classes. If bases is NULL, the Py_tp_bases slot is used instead. If that also is NULL, the Py_tp_base slot is used instead. If that also is NULL, the new type derives from 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 PyType_GetModule(). The associated module is not inherited by subclasses; it must be specified for each class individually.

This function calls PyType_Ready() on the new type.

Note that this function does not fully match the behavior of calling type() or using the class statement. With user-provided base types or metaclasses, prefer calling type (or the metaclass) over PyType_From* functions. Specifically:

Added in version 3.12.

PyObject *PyType_FromModuleAndSpec(PyObject *module, PyType_Spec *spec, PyObject *bases)
Return value: New reference. Part of the Stable ABI since version 3.10.

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

Added in version 3.9.

Changed in version 3.10: The function now accepts a single class as the bases argument and NULL as the tp_doc slot.

Changed in version 3.12: The function now finds and uses a metaclass corresponding to the provided base classes. Previously, only type instances were returned.

The tp_new of the metaclass is ignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_new is deprecated and in Python 3.14+ it will be no longer allowed.

PyObject *PyType_FromSpecWithBases(PyType_Spec *spec, PyObject *bases)
Return value: New reference. Part of the Stable ABI since version 3.3.

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

Added in version 3.3.

Changed in version 3.12: The function now finds and uses a metaclass corresponding to the provided base classes. Previously, only type instances were returned.

The tp_new of the metaclass is ignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_new is deprecated and in Python 3.14+ it will be no longer allowed.

PyObject *PyType_FromSpec(PyType_Spec *spec)
Return value: New reference. Part of the Stable ABI.

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

Changed in version 3.12: The function now finds and uses a metaclass corresponding to the base classes provided in Py_tp_base[s] slots. Previously, only type instances were returned.

The tp_new of the metaclass is ignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_new is deprecated and in Python 3.14+ it will be no longer allowed.

type PyType_Spec
Part of the Stable ABI (including all members).

Structure defining a type’s behavior.

const char *name

Name of the type, used to set PyTypeObject.tp_name.

int basicsize

If positive, specifies the size of the instance in bytes. It is used to set PyTypeObject.tp_basicsize.

If zero, specifies that tp_basicsize should be inherited.

If negative, the absolute value specifies how much space instances of the class need in addition to the superclass. Use PyObject_GetTypeData() to get a pointer to subclass-specific memory reserved this way.

Changed in version 3.12: Previously, this field could not be negative.

int itemsize

Size of one element of a variable-size type, in bytes. Used to set PyTypeObject.tp_itemsize. See tp_itemsize documentation for caveats.

If zero, tp_itemsize is inherited. Extending arbitrary variable-sized classes is dangerous, since some types use a fixed offset for variable-sized memory, which can then overlap fixed-sized memory used by a subclass. To help prevent mistakes, inheriting itemsize is only possible in the following situations:

unsigned int flags

Type flags, used to set PyTypeObject.tp_flags.

If the Py_TPFLAGS_HEAPTYPE flag is not set, PyType_FromSpecWithBases() sets it automatically.

PyType_Slot *slots

Array of PyType_Slot structures. Terminated by the special slot value {0, NULL}.

Each slot ID should be specified at most once.

type PyType_Slot
Part of the Stable ABI (including all members).

Structure defining optional functionality of a type, containing a slot ID and a value pointer.

int slot

A slot ID.

Slot IDs are named like the field names of the structures PyTypeObject, PyNumberMethods, PySequenceMethods, PyMappingMethods and PyAsyncMethods with an added Py_ prefix. For example, use:

The following “offset” fields cannot be set using PyType_Slot:

If it is not possible to switch to a MANAGED flag (for example, for vectorcall or to support Python older than 3.12), specify the offset in Py_tp_members. See PyMemberDef documentation for details.

The following fields cannot be set at all when creating a heap type:

Setting Py_tp_bases or Py_tp_base may be problematic on some platforms. To avoid issues, use the bases argument of PyType_FromSpecWithBases() instead.

Changed in version 3.9: Slots in PyBufferProcs may be set in the unlimited API.

Changed in version 3.11: bf_getbuffer and bf_releasebuffer are now available under the limited API.

void *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.