Type Objects


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.

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.

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).


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}.


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:

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

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

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.