Type Objects

type PyTypeObject
Part of the Stable ABI (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.

In free-threaded builds, PyType_AddWatcher() is not thread-safe, so it must be called at start up (before spawning the first thread).

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.

int PyType_Unwatch(int watcher_id, PyObject *type)

Mark type as not watched. This undoes a previous call to PyType_Watch(). type must not be NULL.

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

On success, this function returns 0. On failure, this function returns -1 with an exception set.

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_FastSubclass(PyTypeObject *type, int flag)

Return non-zero if the type object type sets the subclass flag flag. Subclass flags are denoted by Py_TPFLAGS_*_SUBCLASS. This function is used by many _Check functions for common types.

See also

PyObject_TypeCheck(), which is used as a slower alternative in _Check functions for types that don’t come with subclass 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. Uses Python’s default memory allocation mechanism to allocate memory for a new instance, zeros the memory, then initializes the memory as if by calling PyObject_Init() or PyObject_InitVar().

Do not call this directly to allocate memory for an object; call the type’s tp_alloc slot instead.

For types that support garbage collection (i.e., the Py_TPFLAGS_HAVE_GC flag is set), this function behaves like PyObject_GC_New or PyObject_GC_NewVar (except the memory is guaranteed to be zeroed before initialization), and should be paired with PyObject_GC_Del() in tp_free. Otherwise, it behaves like PyObject_New or PyObject_NewVar (except the memory is guaranteed to be zeroed before initialization) and should be paired with PyObject_Free() in tp_free.

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. Creates a new instance using the type’s tp_alloc slot and returns the resulting object.

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.

PyObject *PyType_GetFullyQualifiedName(PyTypeObject *type)
Part of the Stable ABI since version 3.13.

Return the type’s fully qualified name. Equivalent to f"{type.__module__}.{type.__qualname__}", or type.__qualname__ if type.__module__ is not a string or is equal to "builtins".

Added in version 3.13.

PyObject *PyType_GetModuleName(PyTypeObject *type)
Part of the Stable ABI since version 3.13.

Return the type’s module name. Equivalent to getting the type.__module__ attribute.

Added in version 3.13.

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)
Return value: Borrowed reference. 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().

The returned reference is borrowed from type, and will be valid as long as you hold a reference to type. Do not release it with Py_DECREF() or similar.

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_GetModuleByToken() 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_GetModuleByToken(PyTypeObject *type, const void *mod_token)
Return value: New reference. Part of the Stable ABI since version 3.15.

Find the first superclass whose module has the given module token, 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 3.15.

PyObject *PyType_GetModuleByDef(PyTypeObject *type, struct PyModuleDef *def)
Return value: Borrowed reference. Part of the Stable ABI since version 3.13.

Find the first superclass whose module was created from the given PyModuleDef def, or whose module token is equal to def, and return that module.

Note that modules created from a PyModuleDef always have their token set to the PyModuleDef’s address. In other words, this function is equivalent to PyType_GetModuleByToken(), except that it:

  • returns a borrowed reference, and

  • has a non-void* argument type (which is a cosmetic difference in C).

The returned reference is borrowed from type, and will be valid as long as you hold a reference to type. Do not release it with Py_DECREF() or similar.

Added in version 3.11.

int PyType_GetBaseByToken(PyTypeObject *type, void *tp_token, PyTypeObject **result)
Part of the Stable ABI since version 3.14.

Find the first superclass in type’s method resolution order whose Py_tp_token token is equal to tp_token.

  • If found, set *result to a new strong reference to it and return 1.

  • If not found, set *result to NULL and return 0.

  • On error, set *result to NULL and return -1 with an exception set.

The result argument may be NULL, in which case *result is not set. Use this if you need only the return value.

The tp_token argument may not be NULL.

Added in version 3.14.

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.

int PyType_SUPPORTS_WEAKREFS(PyTypeObject *type)

Return true if instances of type support creating weak references, false otherwise. This function always succeeds. type must not be NULL.

See also

Creating Heap-Allocated Types

The following function is used to create heap types:

PyObject *PyType_FromSlots(const PySlot *slots)
Part of the Stable ABI since version 3.15.

Create and return a heap type from a PySlot array. See Definition slots for general information on slots, and Type slot IDs for slots specific to type creation.

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:

Slots are typically defined as a global static constant arrays. However, sometimes slot values are not statically known at compile time. For example, slots like Py_tp_bases, Py_tp_metaclass and Py_tp_module require live Python objects. In this case, it is recommended to put such slots on the stack, and use Py_slot_subslots to refer to an array of static slots. For example:

static const PySlot my_slots[] = {
   PySlot_STATIC_DATA(Py_tp_name, "MyClass"),
   PySlot_FUNC(Py_tp_repr, my_repr_func),
   ...
   PySlot_END
};

PyObject *make_my_class(PyObject *module) {
   PySlot all_slots[] = {
      PySlot_STATIC_DATA(Py_slot_subslots, my_slots),
      PySlot_DATA(Py_tp_module, module),
      PySlot_END
   };
   return PyType_FromSlots(all_slots);
}

Heap types created without the Py_TPFLAGS_IMMUTABLETYPE flag may be modified, for example by setting attributes on them, as with classes defined in Python code. Sometimes, such modifications are necessary to fully initialize a type, but you may wish to prevent users from changing the type after the initialization is done:

int PyType_Freeze(PyTypeObject *type)
Part of the Stable ABI since version 3.14.

Make a type immutable: set the Py_TPFLAGS_IMMUTABLETYPE flag.

All base classes of type must be immutable.

On success, return 0. On error, set an exception and return -1.

The type must not be used before it’s made immutable. For example, type instances must not be created before the type is made immutable.

Added in version 3.14.

Type slot IDs

Most type 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 slots need additional considerations when specified as slots:

Additional slots do not directly correspond to a PyTypeObject struct field:

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

The Py_tp_base slot is equivalent to Py_tp_bases; both may be set either to a type or a tuple of types. If both are specified, the value of Py_tp_bases is used.

Slot values may not be NULL, except for the following:

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.

Changed in version 3.14: The field tp_vectorcall can now be set using Py_tp_vectorcall. See the field’s documentation for details.

The following slots correspond to fields in the underlying type structure, but need extra remarks for use as slots:

Py_tp_name
Part of the Stable ABI since version 3.15.

Slot ID for the name of the type, used to set PyTypeObject.tp_name.

This slot (or PyType_Spec.name()) is required to create a type.

This may not be used in PyType_Spec.slots. Use PyType_Spec.name() instead.

CPython implementation detail: CPython processes slots in order. It is recommended to put Py_tp_name at the beginning of the slots array, so that if processing of a later slots fails, error messages can include the name.

Added in version 3.15.0a8 (unreleased).

Py_tp_basicsize
Part of the Stable ABI since version 3.15.

Slot ID for the size of the instance in bytes. It is used to set PyTypeObject.tp_basicsize.

The value must be positive.

This may not be used in PyType_Spec.slots. Use PyType_Spec.basicsize() instead.

This slot may not be used with PyType_GetSlot(). Use PyTypeObject.tp_basicsize instead if needed, but be aware that a type’s size is often considered an implementation detail.

Added in version 3.15.0a8 (unreleased).

Py_tp_extra_basicsize
Part of the Stable ABI since version 3.15.

Slot ID for type data size in bytes, that is, how much space instances of the class need in addition to space needed for superclasses.

The value is used, together with the size of superclasses, to set PyTypeObject.tp_basicsize. Python will insert padding as needed to meet tp_basicsize’s alignment requirements.

Use PyObject_GetTypeData() to get a pointer to subclass-specific memory reserved this way.

The value must be positive. To specify that instances need no additional size (that is, size should be inherited), omit the Py_tp_extra_basicsize slot rather than set it to zero.

Specifying both Py_tp_basicsize and Py_tp_extra_basicsize is an error.

This may not be used in PyType_Spec.slots. Use negative PyType_Spec.basicsize() instead.

This slot may not be used with PyType_GetSlot().

Added in version 3.15.0a8 (unreleased).

Py_tp_itemsize
Part of the Stable ABI since version 3.15.

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

The value must be positive.

If this slot is missing, 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:

This may not be used in PyType_Spec.slots. Use PyType_Spec.itemsize() instead.

This slot may not be used with PyType_GetSlot().

Added in version 3.15.0a8 (unreleased).

Py_tp_flags
Part of the Stable ABI since version 3.15.

Slot ID for type flags, used to set PyTypeObject.tp_flags.

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

This may not be used in PyType_Spec.slots. Use negative PyType_Spec.basicsize() instead.

This slot may not be used with PyType_GetSlot(). Use PyType_GetFlags() instead.

Added in version 3.15.0a8 (unreleased).

The following slots do not correspond to public fields in the underlying structures:

Py_tp_metaclass
Part of the Stable ABI since version 3.15.

Slot ID for the metaclass used to construct the resulting type object. When omitted the metaclass is derived from bases (Py_tp_bases or the bases argument of PyType_FromMetaclass()).

Metaclasses that override tp_new are not supported, except if tp_new is NULL.

This may not be used in PyType_Spec.slots. Use PyType_FromMetaclass() to specify a metaclass with PyType_Spec.

This slot may not be used with PyType_GetSlot(). Use Py_TYPE() on the type object instead.

Added in version 3.15.0a8 (unreleased).

Py_tp_module
Part of the Stable ABI since version 3.15.

Slot ID for recording the module in which the new class is defined.

The value must be a module object. 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 may not be used in PyType_Spec.slots. Use PyType_FromMetaclass() to specify a module with PyType_Spec.

This slot may not be used with PyType_GetSlot(). Use PyType_GetModule() instead.

Added in version 3.15.0a8 (unreleased).

Py_tp_token
Part of the Stable ABI since version 3.14.

Slot ID for recording a static memory layout ID for a class.

If the class is defined using a PyType_Spec, and that spec is statically allocated, the token can be set to the spec using the special value Py_TP_USE_SPEC:

static PyType_Slot foo_slots[] = {
   {Py_tp_token, Py_TP_USE_SPEC},

It can also be set to an arbitrary pointer, but you must ensure that:

  • The pointer outlives the class, so it’s not reused for something else while the class exists.

  • It “belongs” to the extension module where the class lives, so it will not clash with other extensions.

Use PyType_GetBaseByToken() to check if a class’s superclass has a given token – that is, check whether the memory layout is compatible.

To get the token for a given class (without considering superclasses), use PyType_GetSlot() with Py_tp_token.

Added in version 3.14.

Py_TP_USE_SPEC
Part of the Stable ABI since version 3.14.

Used as a value with Py_tp_token to set the token to the class’s PyType_Spec. May only be used for classes defined using PyType_Spec.

Expands to NULL.

Added in version 3.14.

Py_tp_slots
Part of the Stable ABI since version 3.15.

Slot ID that works like Py_slot_subslots, except it specifies an array of PyType_Slot structures.

Added in version 3.15.0a8 (unreleased).

Soft-deprecated API

The following functions are soft deprecated. They will continue to work, but new features will be added as slots for PyType_FromSlots(), not as arguments to new PyType_From* functions.

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).

A non-NULL metaclass argument corresponds to the Py_tp_metaclass slot.

A non-NULL bases argument corresponds to the Py_tp_bases slot, and takes precedence over Py_tp_bases and Py_tp_bases slots.

A non-NULL module argument corresponds to the Py_tp_module slot.

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. See the note in PyType_FromSlots() documentation for details.

Added in version 3.12.

Soft deprecated since version 3.15.0a8 (unreleased): Prefer PyType_FromSlots() in new code.

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.

Changed in version 3.14: Creating classes whose metaclass overrides tp_new is no longer allowed.

Soft deprecated since version 3.15.0a8 (unreleased): Prefer PyType_FromSlots() in new code.

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.

Changed in version 3.14: Creating classes whose metaclass overrides tp_new is no longer allowed.

Soft deprecated since version 3.15.0a8 (unreleased): Prefer PyType_FromSlots() in new code.

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.

Changed in version 3.14: Creating classes whose metaclass overrides tp_new is no longer allowed.

Soft deprecated since version 3.15.0a8 (unreleased): Prefer PyType_FromSlots() in new code.

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

Structure defining a type’s behavior, used for soft-deprecated functions like PyType_FromMetaclass().

This structure contains several members that can instead be specified as slots for PyType_FromSlots(), and an array of slot entries with a simpler structure.

const char *name

Corresponds to Py_tp_name.

int basicsize

If positive, corresponds to Py_tp_basicsize.

If negative, corresponds to Py_tp_extra_basicsize set to the absolute value.

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

int itemsize

Corresponds to Py_tp_itemsize.

unsigned int flags

Corresponds to Py_tp_flags.

PyType_Slot *slots

Array of PyType_Slot (not PySlot) 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, used for soft-deprecated functions like PyType_FromMetaclass().

Note that a PyType_Slot array may be included in a PySlot array using Py_tp_slots, and vice versa using Py_slot_subslots.

Each PyType_Slot structure tpslot is interpreted as the following PySlot structure:

(PySlot){
   .sl_id=tpslot.slot,
   .sl_flags=PySlot_INTPTR | sub_static,
   .sl_ptr=tpslot.func
}

where sub_static is PySlot_STATIC if the slot requires the flag (such as for Py_tp_methods), or if this flag is present on the “parent” Py_tp_slots slot (if any).

int slot

Corresponds to PySlot.sl_id.

void *pfunc

Corresponds to PySlot.sl_ptr.