# Type Objects

`PyTypeObject`

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

PyObject* `PyType_Type`

  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`()

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

unsigned long `PyType_GetFlags`(PyTypeObject* type)

  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.

  New in version 3.2.

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

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.

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)

  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.

  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.

  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)

  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.

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 `PyType_Slot.slot` for possible values of the slot argument.

  An exception is raised if type is not a heap type.

  New in version 3.4.

PyObject* `PyType_GetModule`(PyTypeObject *type)

  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.

  New in version 3.9.

void* `PyType_GetModuleState`(PyTypeObject *type)

  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.

  New in version 3.9.

## Creating Heap-Allocated Types

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

PyObject* `PyType_FromModuleAndSpec`(PyObject *module, PyType_Spec *spec, PyObject *bases)
  Return value: New reference.

  Creates and returns a heap type object from the spec (`Py_TPFLAGS_HEAPTYPE`).

  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_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 retreived 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.

  New in version 3.9.

PyObject* `PyType_FromSpecWithBases`(PyType_Spec *spec, PyObject *bases)
  Return value: New reference.

  Equivalent to `PyType_FromModuleAndSpec(NULL, spec, bases)`.

  New in version 3.3.

PyObject* `PyType_FromSpec`(PyType_Spec *spec)
  Return value: New reference.

  Equivalent to `PyType_FromSpecWithBases(spec, NULL)`.

`PyType_Spec`

  Structure defining a type’s behavior.

  const char* `PyType_Spec.name`

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

  int `PyType_Spec.basicsize`
  int `PyType_Spec.itemsize`

    Size of the instance in bytes, used to set `PyTypeObject.tp_basicsize` and `PyTypeObject.tp_itemsize`.

  int `PyType_Spec.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 *`PyType_Spec.slots`

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

`PyType_Slot`

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

  int `PyType_Slot.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:

    > - `Py_tp_dealloc` to set `PyTypeObject.tp_dealloc`
    > - `Py_nb_add` to set `PyNumberMethods.nb_add`
    > - `Py_sq_length` to set `PySequenceMethods.sq_length`

    > The following fields cannot be set at all using `PyType_Spec` and `PyType_Slot`:

    > - `tp_dict`
    > - `tp_mro`
    > - `tp_cache`
    > - `tp_subclasses`
    > - `tp_weaklist`
    > - `tp_vectorcall`
    > - `tp_weaklistoffset` (see PyMemberDef)
    > - `tp_dictoffset` (see PyMemberDef)
    > - `tp_vectorcall_offset` (see PyMemberDef)

    > The following fields cannot be set using `PyType_Spec` and `PyType_Slot` under the limited API:

    > - `bf_getbuffer`
    > - `bf_releasebuffer`

    > 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` in may be set in the unlimited API.

  void *`PyType_Slot.pfunc`

    The desired value of the slot. In most cases, this is a pointer to a function.

    May not be `NULL`.