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.

   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_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)
    *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*, 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.

   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 *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 the given one.

   * 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 *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:

     * Weak Reference Objects

     * "weakref"


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".

   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:

   * "__new__()" is not called on the new class (and it must be set to
     "type.__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 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.

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.

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.

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 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. For negative "basicsize", Python will
      insert padding when needed to meet "tp_basicsize"’s alignment
      requirements.

      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:

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

      * The requested "PyType_Spec.basicsize" is positive, suggesting
        that the memory layout of the base class is known.

      * The requested "PyType_Spec.basicsize" is zero, suggesting that
        the subclass does not access the instance’s memory directly.

      * With the "Py_TPFLAGS_ITEMS_AT_END" flag.

   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:

      * "Py_tp_dealloc" to set "PyTypeObject.tp_dealloc"

      * "Py_nb_add" to set "PyNumberMethods.nb_add"

      * "Py_sq_length" to set "PySequenceMethods.sq_length"

      An additional slot is supported that does not correspond to a
      "PyTypeObject" struct field:

      * "Py_tp_token"

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

      * "tp_weaklistoffset" (use "Py_TPFLAGS_MANAGED_WEAKREF" instead
        if possible)

      * "tp_dictoffset" (use "Py_TPFLAGS_MANAGED_DICT" instead if
        possible)

      * "tp_vectorcall_offset" (use ""__vectorcalloffset__"" in
        PyMemberDef)

      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:

      * "tp_dict", "tp_mro", "tp_cache", "tp_subclasses", and
        "tp_weaklist".

      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.

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

   void *pfunc

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

      *pfunc* values may not be "NULL", except for the following
      slots:

      * "Py_tp_doc"

      * "Py_tp_token" (for clarity, prefer "Py_TP_USE_SPEC" rather
        than "NULL")

Py_tp_token
    * Part of the Stable ABI since version 3.14.*

   A "slot" that records a static memory layout ID for a class.

   If the "PyType_Spec" of the class 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". Expands to "NULL".

      Added in version 3.14.
