Type Objects

typePyTypeObject

Part of theLimited API(as an opaque struct).

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

PyTypeObjectPyType_Type

Part of theStable ABI.

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

intPyType_Check(PyObject*o)

Return non-zero if the objectois a type object, including instances of types derived from the standard type object. Return 0 in all other cases. This function always succeeds.

intPyType_CheckExact(PyObject*o)

Return non-zero if the objectois a type object, but not a subtype of the standard type object. Return 0 in all other cases. This function always succeeds.

unsignedintPyType_ClearCache()

Part of theStable ABI.

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

unsignedlongPyType_GetFlags(PyTypeObject*type)

Part of theStable ABI.

Return thetp_flagsmember oftype.This function is primarily meant for use withPy_LIMITED_API;the individual flag bits are guaranteed to be stable across Python releases, but access to tp_flagsitself is not part of thelimited API.

Added in version 3.2.

Changed in version 3.4:The return type is nowunsignedlongrather thanlong.

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 accessingtp_dictdirectly. 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 orPyObject_GetAttr()) isn’t adequate.

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

Added in version 3.12.

voidPyType_Modified(PyTypeObject*type)

Part of theStable 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.

intPyType_AddWatcher(PyType_WatchCallbackcallback)

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

Added in version 3.12.

intPyType_ClearWatcher(intwatcher_id)

Clear watcher identified bywatcher_id(previously returned from PyType_AddWatcher()). Return0on success,-1on error (e.g. ifwatcher_idwas never registered.)

An extension should never callPyType_ClearWatcherwith awatcher_id that was not returned to it by a previous call to PyType_AddWatcher().

Added in version 3.12.

intPyType_Watch(intwatcher_id,PyObject*type)

Marktypeas watched. The callback grantedwatcher_idby PyType_AddWatcher()will be called whenever PyType_Modified()reports a change totype.(The callback may be called only once for a series of consecutive modifications totype,if _PyType_Lookup()is not called ontypebetween the modifications; this is an implementation detail and subject to change.)

An extension should never callPyType_Watchwith awatcher_idthat was not returned to it by a previous call toPyType_AddWatcher().

Added in version 3.12.

typedefint(*PyType_WatchCallback)(PyObject*type)

Type of a type-watcher callback function.

The callback must not modifytypeor causePyType_Modified()to be called ontypeor any type in its MRO; violating this rule could cause infinite recursion.

Added in version 3.12.

intPyType_HasFeature(PyTypeObject*o,intfeature)

Return non-zero if the type objectosets the featurefeature. Type features are denoted by single bit flags.

intPyType_IS_GC(PyTypeObject*o)

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

intPyType_IsSubtype(PyTypeObject*a,PyTypeObject*b)

Part of theStable ABI.

Return true ifais a subtype ofb.

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

PyObject*PyType_GenericAlloc(PyTypeObject*type,Py_ssize_tnitems)

Return value: New reference.Part of theStable ABI.

Generic handler for thetp_allocslot of a type object. Use Python’s default memory allocation mechanism to allocate a new instance and initialize all its contents toNULL.

PyObject*PyType_GenericNew(PyTypeObject*type,PyObject*args,PyObject*kwds)

Return value: New reference.Part of theStable ABI.

Generic handler for thetp_newslot of a type object. Create a new instance using the type’stp_allocslot.

intPyType_Ready(PyTypeObject*type)

Part of theStable 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. Return0on success, or return-1and sets an exception on error.

Note

If some of the base classes implements the GC protocol and the provided type does not include thePy_TPFLAGS_HAVE_GCin 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_GCin its flags then itmustimplement the GC protocol itself by at least implementing the tp_traversehandle.

PyObject*PyType_GetName(PyTypeObject*type)

Return value: New reference.Part of theStable ABIsince 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 theStable ABIsince 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,intslot)

Part of theStable ABIsince version 3.4.

Return the function pointer stored in the given slot. If the result isNULL,this indicates that either the slot isNULL, or that the function was called with invalid parameters. Callers will typically cast the result pointer into the appropriate function type.

SeePyType_Slot.slotfor possible values of theslotargument.

Added in version 3.4.

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

PyObject*PyType_GetModule(PyTypeObject*type)

Part of theStable ABIsince version 3.10.

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

If no module is associated with the given type, setsTypeError and returnsNULL.

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 asubclassof the intended class, and subclasses are not necessarily defined in the same module as their superclass. SeePyCMethodto get the class that defines the method. SeePyType_GetModuleByDef()for cases whenPyCMethodcannot be used.

Added in version 3.9.

void*PyType_GetModuleState(PyTypeObject*type)

Part of theStable ABIsince version 3.10.

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

If no module is associated with the given type, setsTypeError and returnsNULL.

If thetypehas an associated module but its state isNULL, returnsNULLwithout setting an exception.

Added in version 3.9.

PyObject*PyType_GetModuleByDef(PyTypeObject*type,structPyModuleDef*def)

Find the first superclass whose module was created from the givenPyModuleDefdef,and return that module.

If no module is found, raises aTypeErrorand returnsNULL.

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

Added in version 3.11.

intPyUnstable_Type_AssignVersionTag(PyTypeObject*type)

This isUnstable 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 theStable ABIsince version 3.12.

Create and return aheap typefrom thespec (seePy_TPFLAGS_HEAPTYPE).

The metaclassmetaclassis used to construct the resulting type object. WhenmetaclassisNULL,the metaclass is derived frombases (orPy_tp_base[s]slots ifbasesisNULL,see below).

Metaclasses that overridetp_neware not supported, except iftp_newisNULL. (For backwards compatibility, otherPyType_From*functions allow such metaclasses. They ignoretp_new,which may result in incomplete initialization. This is deprecated and in Python 3.14+ such metaclasses will not be supported.)

Thebasesargument can be used to specify base classes; it can either be only one class or a tuple of classes. IfbasesisNULL,thePy_tp_basesslot is used instead. If that also isNULL,thePy_tp_baseslot is used instead. If that also isNULL,the new type derives fromobject.

Themoduleargument can be used to record the module in which the new class is defined. It must be a module object orNULL. If notNULL,the module is associated with the new type and can later be retrieved withPyType_GetModule(). The associated module is not inherited by subclasses; it must be specified for each class individually.

This function callsPyType_Ready()on the new type.

Note that this function doesnotfully match the behavior of callingtype()or using theclassstatement. With user-provided base types or metaclasses, prefer callingtype(or the metaclass) overPyType_From*functions. Specifically:

• __new__()is not called on the new class (and it must be set totype.__new__).

• __init__()is not called on the new class.

• __init_subclass__()is not called on any bases.

• __set_name__()is not called on new descriptors.

Added in version 3.12.

PyObject*PyType_FromModuleAndSpec(PyObject*module,PyType_Spec*spec,PyObject*bases)

Return value: New reference.Part of theStable ABIsince version 3.10.

Equivalent toPyType_FromMetaclass(NULL,module,spec,bases).

Added in version 3.9.

Changed in version 3.10:The function now accepts a single class as thebasesargument and NULLas thetp_docslot.

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

Thetp_newof the metaclass isignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_newis 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 theStable ABIsince version 3.3.

Equivalent toPyType_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, onlytypeinstances were returned.

Thetp_newof the metaclass isignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_newis deprecated and in Python 3.14+ it will be no longer allowed.

PyObject*PyType_FromSpec(PyType_Spec*spec)

Return value: New reference.Part of theStable ABI.

Equivalent toPyType_FromMetaclass(NULL,NULL,spec,NULL).

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

Thetp_newof the metaclass isignored. which may result in incomplete initialization. Creating classes whose metaclass overrides tp_newis deprecated and in Python 3.14+ it will be no longer allowed.

typePyType_Spec

Part of theStable ABI(including all members).

Structure defining a type’s behavior.

constchar*name

Name of the type, used to setPyTypeObject.tp_name.

intbasicsize

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

If zero, specifies thattp_basicsize should be inherited.

If negative, the absolute value specifies how much space instances of the class needin additionto the superclass. UsePyObject_GetTypeData()to get a pointer to subclass-specific memory reserved this way.

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

intitemsize

Size of one element of a variable-size type, in bytes. Used to setPyTypeObject.tp_itemsize. Seetp_itemsizedocumentation for caveats.

If zero,tp_itemsizeis 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, inheritingitemsizeis only possible in the following situations:

• The base is not variable-sized (its tp_itemsize).

• The requestedPyType_Spec.basicsizeis positive, suggesting that the memory layout of the base class is known.

• The requestedPyType_Spec.basicsizeis zero, suggesting that the subclass does not access the instance’s memory directly.

• With thePy_TPFLAGS_ITEMS_AT_ENDflag.

unsignedintflags

Type flags, used to setPyTypeObject.tp_flags.

If thePy_TPFLAGS_HEAPTYPEflag is not set, PyType_FromSpecWithBases()sets it automatically.

PyType_Slot*slots

Array ofPyType_Slotstructures. Terminated by the special slot value{0,NULL}.

Each slot ID should be specified at most once.

typePyType_Slot

Part of theStable ABI(including all members).

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

intslot

A slot ID.

Slot IDs are named like the field names of the structures PyTypeObject,PyNumberMethods, PySequenceMethods,PyMappingMethodsand PyAsyncMethodswith an addedPy_prefix. For example, use:

• Py_tp_deallocto setPyTypeObject.tp_dealloc

• Py_nb_addto setPyNumberMethods.nb_add

• Py_sq_lengthto setPySequenceMethods.sq_length

The following “offset” fields cannot be set usingPyType_Slot:

• tp_weaklistoffset (usePy_TPFLAGS_MANAGED_WEAKREFinstead if possible)

• tp_dictoffset (usePy_TPFLAGS_MANAGED_DICTinstead if possible)

• tp_vectorcall_offset (use"__vectorcalloffset__"in PyMemberDef)

If it is not possible to switch to aMANAGEDflag (for example, for vectorcall or to support Python older than 3.12), specify the offset inPy_tp_members. SeePyMemberDef documentation for details.

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

• tp_vectorcall (usetp_newand/or tp_init)

• Internal fields: tp_dict, tp_mro, tp_cache, tp_subclasses,and tp_weaklist.

SettingPy_tp_basesorPy_tp_basemay be problematic on some platforms. To avoid issues, use thebasesargument of PyType_FromSpecWithBases()instead.

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

Changed in version 3.11:bf_getbufferand bf_releasebufferare now available under thelimited API.

void*pfunc

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

Slots other thanPy_tp_docmay not beNULL.