.. highlight:: c

.. _object:

Object Protocol
===============


.. c:function:: PyObject* Py_GetConstant(unsigned int constant_id)

   Get a :term:`strong reference` to a constant.

   Set an exception and return ``NULL`` if *constant_id* is invalid.

   *constant_id* must be one of these constant identifiers:

   .. c:namespace:: NULL

   ========================================  =====  =========================
   Constant Identifier                       Value  Returned object
   ========================================  =====  =========================
   .. c:macro:: Py_CONSTANT_NONE             ``0``  :py:data:`None`
   .. c:macro:: Py_CONSTANT_FALSE            ``1``  :py:data:`False`
   .. c:macro:: Py_CONSTANT_TRUE             ``2``  :py:data:`True`
   .. c:macro:: Py_CONSTANT_ELLIPSIS         ``3``  :py:data:`Ellipsis`
   .. c:macro:: Py_CONSTANT_NOT_IMPLEMENTED  ``4``  :py:data:`NotImplemented`
   .. c:macro:: Py_CONSTANT_ZERO             ``5``  ``0``
   .. c:macro:: Py_CONSTANT_ONE              ``6``  ``1``
   .. c:macro:: Py_CONSTANT_EMPTY_STR        ``7``  ``''``
   .. c:macro:: Py_CONSTANT_EMPTY_BYTES      ``8``  ``b''``
   .. c:macro:: Py_CONSTANT_EMPTY_TUPLE      ``9``  ``()``
   ========================================  =====  =========================

   Numeric values are only given for projects which cannot use the constant
   identifiers.


   .. versionadded:: 3.13

   .. impl-detail::

      In CPython, all of these constants are :term:`immortal`.


.. c:function:: PyObject* Py_GetConstantBorrowed(unsigned int constant_id)

   Similar to :c:func:`Py_GetConstant`, but return a :term:`borrowed
   reference`.

   This function is primarily intended for backwards compatibility:
   using :c:func:`Py_GetConstant` is recommended for new code.

   The reference is borrowed from the interpreter, and is valid until the
   interpreter finalization.

   .. versionadded:: 3.13


.. c:var:: PyObject* Py_NotImplemented

   The ``NotImplemented`` singleton, used to signal that an operation is
   not implemented for the given type combination.


.. c:macro:: Py_RETURN_NOTIMPLEMENTED

   Properly handle returning :c:data:`Py_NotImplemented` from within a C
   function (that is, create a new :term:`strong reference`
   to :const:`NotImplemented` and return it).


.. c:macro:: Py_PRINT_RAW

   Flag to be used with multiple functions that print the object (like
   :c:func:`PyObject_Print` and :c:func:`PyFile_WriteObject`).
   If passed, these functions use the :func:`str` of the object
   instead of the :func:`repr`.


.. c:function:: int PyObject_Print(PyObject *o, FILE *fp, int flags)

   Print an object *o*, on file *fp*.  Returns ``-1`` on error.  The flags argument
   is used to enable certain printing options.  The only option currently supported
   is :c:macro:`Py_PRINT_RAW`; if given, the :func:`str` of the object is written
   instead of the :func:`repr`.


.. c:function:: void PyObject_Dump(PyObject *op)

   Dump an object *op* to ``stderr``. This should only be used for debugging.

   The output is intended to try dumping objects even after memory corruption:

   * Information is written starting with fields that are the least likely to
     crash when accessed.
   * This function can be called without an :term:`attached thread state`, but
     it's not recommended to do so: it can cause deadlocks.
   * An object that does not belong to the current interpreter may be dumped,
     but this may also cause crashes or unintended behavior.
   * Implement a heuristic to detect if the object memory has been freed. Don't
     display the object contents in this case, only its memory address.
   * The output format may change at any time.

   Example of output:

   .. code-block:: output

       object address  : 0x7f80124702c0
       object refcount : 2
       object type     : 0x9902e0
       object type name: str
       object repr     : 'abcdef'

   .. versionadded:: 3.15


.. c:function:: int PyObject_HasAttrWithError(PyObject *o, PyObject *attr_name)

   Returns ``1`` if *o* has the attribute *attr_name*, and ``0`` otherwise.
   This is equivalent to the Python expression ``hasattr(o, attr_name)``.
   On failure, return ``-1``.

   .. versionadded:: 3.13


.. c:function:: int PyObject_HasAttrStringWithError(PyObject *o, const char *attr_name)

   This is the same as :c:func:`PyObject_HasAttrWithError`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   .. versionadded:: 3.13


.. c:function:: int PyObject_HasAttr(PyObject *o, PyObject *attr_name)

   Returns ``1`` if *o* has the attribute *attr_name*, and ``0`` otherwise.
   This function always succeeds.

   .. note::

      Exceptions that occur when this calls :meth:`~object.__getattr__` and
      :meth:`~object.__getattribute__` methods aren't propagated,
      but instead given to :func:`sys.unraisablehook`.
      For proper error handling, use :c:func:`PyObject_HasAttrWithError`,
      :c:func:`PyObject_GetOptionalAttr` or :c:func:`PyObject_GetAttr` instead.


.. c:function:: int PyObject_HasAttrString(PyObject *o, const char *attr_name)

   This is the same as :c:func:`PyObject_HasAttr`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   .. note::

      Exceptions that occur when this calls :meth:`~object.__getattr__` and
      :meth:`~object.__getattribute__` methods or while creating the temporary
      :class:`str` object are silently ignored.
      For proper error handling, use :c:func:`PyObject_HasAttrStringWithError`,
      :c:func:`PyObject_GetOptionalAttrString`
      or :c:func:`PyObject_GetAttrString` instead.


.. c:function:: PyObject* PyObject_GetAttr(PyObject *o, PyObject *attr_name)

   Retrieve an attribute named *attr_name* from object *o*. Returns the attribute
   value on success, or ``NULL`` on failure.  This is the equivalent of the Python
   expression ``o.attr_name``.

   If the missing attribute should not be treated as a failure, you can use
   :c:func:`PyObject_GetOptionalAttr` instead.


.. c:function:: PyObject* PyObject_GetAttrString(PyObject *o, const char *attr_name)

   This is the same as :c:func:`PyObject_GetAttr`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   If the missing attribute should not be treated as a failure, you can use
   :c:func:`PyObject_GetOptionalAttrString` instead.


.. c:function:: int PyObject_GetOptionalAttr(PyObject *obj, PyObject *attr_name, PyObject **result);

   Variant of :c:func:`PyObject_GetAttr` which doesn't raise
   :exc:`AttributeError` if the attribute is not found.

   If the attribute is found, return ``1`` and set *\*result* to a new
   :term:`strong reference` to the attribute.
   If the attribute is not found, return ``0`` and set *\*result* to ``NULL``;
   the :exc:`AttributeError` is silenced.
   If an error other than :exc:`AttributeError` is raised, return ``-1`` and
   set *\*result* to ``NULL``.

   .. versionadded:: 3.13


.. c:function:: int PyObject_GetOptionalAttrString(PyObject *obj, const char *attr_name, PyObject **result);

   This is the same as :c:func:`PyObject_GetOptionalAttr`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   .. versionadded:: 3.13

.. c:function:: PyObject* PyObject_GenericGetAttr(PyObject *o, PyObject *name)

   Generic attribute getter function that is meant to be put into a type
   object's ``tp_getattro`` slot.  It looks for a descriptor in the dictionary
   of classes in the object's MRO as well as an attribute in the object's
   :attr:`~object.__dict__` (if present).  As outlined in :ref:`descriptors`,
   data descriptors take preference over instance attributes, while non-data
   descriptors don't.  Otherwise, an :exc:`AttributeError` is raised.


.. c:function:: int PyObject_SetAttr(PyObject *o, PyObject *attr_name, PyObject *v)

   Set the value of the attribute named *attr_name*, for object *o*, to the value
   *v*. Raise an exception and return ``-1`` on failure;
   return ``0`` on success.  This is the equivalent of the Python statement
   ``o.attr_name = v``.

   If *v* is ``NULL``, the attribute is deleted. This behaviour is deprecated
   in favour of using :c:func:`PyObject_DelAttr`, but there are currently no
   plans to remove it.

   The function must not be called with a ``NULL`` *v* and an exception set.
   This case can arise from forgetting ``NULL`` checks and would delete the
   attribute.

   .. versionchanged:: 3.15
      Must not be called with NULL value if an exception is set.


.. c:function:: int PyObject_SetAttrString(PyObject *o, const char *attr_name, PyObject *v)

   This is the same as :c:func:`PyObject_SetAttr`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   If *v* is ``NULL``, the attribute is deleted, but this feature is
   deprecated in favour of using :c:func:`PyObject_DelAttrString`.

   The function must not be called with a ``NULL`` *v* and an exception set.
   This case can arise from forgetting ``NULL`` checks and would delete the
   attribute.

   The number of different attribute names passed to this function
   should be kept small, usually by using a statically allocated string
   as *attr_name*.
   For attribute names that aren't known at compile time, prefer calling
   :c:func:`PyUnicode_FromString` and :c:func:`PyObject_SetAttr` directly.
   For more details, see :c:func:`PyUnicode_InternFromString`, which may be
   used internally to create a key object.

   .. versionchanged:: 3.15
      Must not be called with NULL value if an exception is set.


.. c:function:: int PyObject_GenericSetAttr(PyObject *o, PyObject *name, PyObject *value)

   Generic attribute setter and deleter function that is meant
   to be put into a type object's :c:member:`~PyTypeObject.tp_setattro`
   slot.  It looks for a data descriptor in the
   dictionary of classes in the object's MRO, and if found it takes preference
   over setting or deleting the attribute in the instance dictionary. Otherwise, the
   attribute is set or deleted in the object's :attr:`~object.__dict__` (if present).
   On success, ``0`` is returned, otherwise an :exc:`AttributeError`
   is raised and ``-1`` is returned.


.. c:function:: int PyObject_DelAttr(PyObject *o, PyObject *attr_name)

   Delete attribute named *attr_name*, for object *o*. Returns ``-1`` on failure.
   This is the equivalent of the Python statement ``del o.attr_name``.


.. c:function:: int PyObject_DelAttrString(PyObject *o, const char *attr_name)

   This is the same as :c:func:`PyObject_DelAttr`, but *attr_name* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.

   The number of different attribute names passed to this function
   should be kept small, usually by using a statically allocated string
   as *attr_name*.
   For attribute names that aren't known at compile time, prefer calling
   :c:func:`PyUnicode_FromString` and :c:func:`PyObject_DelAttr` directly.
   For more details, see :c:func:`PyUnicode_InternFromString`, which may be
   used internally to create a key object for lookup.


.. c:function:: PyObject* PyObject_GenericGetDict(PyObject *o, void *context)

   A generic implementation for the getter of a ``__dict__`` descriptor. It
   creates the dictionary if necessary.

   This function may also be called to get the :py:attr:`~object.__dict__`
   of the object *o*. Pass ``NULL`` for *context* when calling it.
   Since this function may need to allocate memory for the
   dictionary, it may be more efficient to call :c:func:`PyObject_GetAttr`
   when accessing an attribute on the object.

   On failure, returns ``NULL`` with an exception set.

   .. versionadded:: 3.3


.. c:function:: int PyObject_GenericSetDict(PyObject *o, PyObject *value, void *context)

   A generic implementation for the setter of a ``__dict__`` descriptor. This
   implementation does not allow the dictionary to be deleted.

   .. versionadded:: 3.3


.. c:function:: PyObject** _PyObject_GetDictPtr(PyObject *obj)

   Return a pointer to :py:attr:`~object.__dict__` of the object *obj*.
   If there is no ``__dict__``, return ``NULL`` without setting an exception.

   This function may need to allocate memory for the
   dictionary, so it may be more efficient to call :c:func:`PyObject_GetAttr`
   when accessing an attribute on the object.


.. c:function:: PyObject* PyObject_RichCompare(PyObject *o1, PyObject *o2, int opid)

   Compare the values of *o1* and *o2* using the operation specified by *opid*,
   which must be one of :c:macro:`Py_LT`, :c:macro:`Py_LE`, :c:macro:`Py_EQ`,
   :c:macro:`Py_NE`, :c:macro:`Py_GT`, or :c:macro:`Py_GE`, corresponding to ``<``,
   ``<=``, ``==``, ``!=``, ``>``, or ``>=`` respectively. This is the equivalent of
   the Python expression ``o1 op o2``, where ``op`` is the operator corresponding
   to *opid*. Returns the value of the comparison on success, or ``NULL`` on failure.


.. c:function:: int PyObject_RichCompareBool(PyObject *o1, PyObject *o2, int opid)

   Compare the values of *o1* and *o2* using the operation specified by *opid*,
   like :c:func:`PyObject_RichCompare`, but returns ``-1`` on error, ``0`` if
   the result is false, ``1`` otherwise.

.. note::
   If *o1* and *o2* are the same object, :c:func:`PyObject_RichCompareBool`
   will always return ``1`` for :c:macro:`Py_EQ` and ``0`` for :c:macro:`Py_NE`.

.. c:function:: PyObject* PyObject_Format(PyObject *obj, PyObject *format_spec)

   Format *obj* using *format_spec*. This is equivalent to the Python
   expression ``format(obj, format_spec)``.

   *format_spec* may be ``NULL``. In this case the call is equivalent
   to ``format(obj)``.
   Returns the formatted string on success, ``NULL`` on failure.

.. c:function:: PyObject* PyObject_Repr(PyObject *o)

   .. index:: pair: built-in function; repr

   Compute a string representation of object *o*.  Returns the string
   representation on success, ``NULL`` on failure.  This is the equivalent of the
   Python expression ``repr(o)``.  Called by the :func:`repr` built-in function.

   .. versionchanged:: 3.4
      This function now includes a debug assertion to help ensure that it
      does not silently discard an active exception.

.. c:function:: PyObject* PyObject_ASCII(PyObject *o)

   .. index:: pair: built-in function; ascii

   As :c:func:`PyObject_Repr`, compute a string representation of object *o*, but
   escape the non-ASCII characters in the string returned by
   :c:func:`PyObject_Repr` with ``\x``, ``\u`` or ``\U`` escapes.  This generates
   a string similar to that returned by :c:func:`PyObject_Repr` in Python 2.
   Called by the :func:`ascii` built-in function.

   .. index:: string; PyObject_Str (C function)


.. c:function:: PyObject* PyObject_Str(PyObject *o)

   Compute a string representation of object *o*.  Returns the string
   representation on success, ``NULL`` on failure.  This is the equivalent of the
   Python expression ``str(o)``.  Called by the :func:`str` built-in function
   and, therefore, by the :func:`print` function.

   .. versionchanged:: 3.4
      This function now includes a debug assertion to help ensure that it
      does not silently discard an active exception.


.. c:function:: PyObject* PyObject_Bytes(PyObject *o)

   .. index:: pair: built-in function; bytes

   Compute a bytes representation of object *o*.  ``NULL`` is returned on
   failure and a bytes object on success.  This is equivalent to the Python
   expression ``bytes(o)``, when *o* is not an integer.  Unlike ``bytes(o)``,
   a TypeError is raised when *o* is an integer instead of a zero-initialized
   bytes object.


.. c:function:: int PyObject_IsSubclass(PyObject *derived, PyObject *cls)

   Return ``1`` if the class *derived* is identical to or derived from the class
   *cls*, otherwise return ``0``.  In case of an error, return ``-1``.

   If *cls* is a tuple, the check will be done against every entry in *cls*.
   The result will be ``1`` when at least one of the checks returns ``1``,
   otherwise it will be ``0``.

   If *cls* has a :meth:`~type.__subclasscheck__` method, it will be called to
   determine the subclass status as described in :pep:`3119`.  Otherwise,
   *derived* is a subclass of *cls* if it is a direct or indirect subclass,
   i.e. contained in :attr:`cls.__mro__ <type.__mro__>`.

   Normally only class objects, i.e. instances of :class:`type` or a derived
   class, are considered classes.  However, objects can override this by having
   a :attr:`~type.__bases__` attribute (which must be a tuple of base classes).


.. c:function:: int PyObject_IsInstance(PyObject *inst, PyObject *cls)

   Return ``1`` if *inst* is an instance of the class *cls* or a subclass of
   *cls*, or ``0`` if not.  On error, returns ``-1`` and sets an exception.

   If *cls* is a tuple, the check will be done against every entry in *cls*.
   The result will be ``1`` when at least one of the checks returns ``1``,
   otherwise it will be ``0``.

   If *cls* has a :meth:`~type.__instancecheck__` method, it will be called to
   determine the subclass status as described in :pep:`3119`.  Otherwise, *inst*
   is an instance of *cls* if its class is a subclass of *cls*.

   An instance *inst* can override what is considered its class by having a
   :attr:`~object.__class__` attribute.

   An object *cls* can override if it is considered a class, and what its base
   classes are, by having a :attr:`~type.__bases__` attribute (which must be a tuple
   of base classes).


.. c:function:: Py_hash_t PyObject_Hash(PyObject *o)

   .. index:: pair: built-in function; hash

   Compute and return the hash value of an object *o*.  On failure, return ``-1``.
   This is the equivalent of the Python expression ``hash(o)``.

   .. versionchanged:: 3.2
      The return type is now Py_hash_t.  This is a signed integer the same size
      as :c:type:`Py_ssize_t`.


.. c:function:: Py_hash_t PyObject_HashNotImplemented(PyObject *o)

   Set a :exc:`TypeError` indicating that ``type(o)`` is not :term:`hashable` and return ``-1``.
   This function receives special treatment when stored in a ``tp_hash`` slot,
   allowing a type to explicitly indicate to the interpreter that it is not
   hashable.


.. c:function:: int PyObject_IsTrue(PyObject *o)

   Returns ``1`` if the object *o* is considered to be true, and ``0`` otherwise.
   This is equivalent to the Python expression ``not not o``.  On failure, return
   ``-1``.


.. c:function:: int PyObject_Not(PyObject *o)

   Returns ``0`` if the object *o* is considered to be true, and ``1`` otherwise.
   This is equivalent to the Python expression ``not o``.  On failure, return
   ``-1``.


.. c:function:: PyObject* PyObject_Type(PyObject *o)

   .. index:: pair: built-in function; type

   When *o* is non-``NULL``, returns a type object corresponding to the object type
   of object *o*. On failure, raises :exc:`SystemError` and returns ``NULL``.  This
   is equivalent to the Python expression ``type(o)``.
   This function creates a new :term:`strong reference` to the return value.
   There's really no reason to use this
   function instead of the :c:func:`Py_TYPE()` function, which returns a
   pointer of type :c:expr:`PyTypeObject*`, except when a new
   :term:`strong reference` is needed.


.. c:function:: int PyObject_TypeCheck(PyObject *o, PyTypeObject *type)

   Return non-zero if the object *o* is of type *type* or a subtype of *type*, and
   ``0`` otherwise.  Both parameters must be non-``NULL``.


.. c:function:: Py_ssize_t PyObject_Size(PyObject *o)
               Py_ssize_t PyObject_Length(PyObject *o)

   .. index:: pair: built-in function; len

   Return the length of object *o*.  If the object *o* provides either the sequence
   and mapping protocols, the sequence length is returned.  On error, ``-1`` is
   returned.  This is the equivalent to the Python expression ``len(o)``.


.. c:function:: Py_ssize_t PyObject_LengthHint(PyObject *o, Py_ssize_t defaultvalue)

   Return an estimated length for the object *o*. First try to return its
   actual length, then an estimate using :meth:`~object.__length_hint__`, and
   finally return the default value. On error return ``-1``. This is the
   equivalent to the Python expression ``operator.length_hint(o, defaultvalue)``.

   .. versionadded:: 3.4


.. c:function:: PyObject* PyObject_GetItem(PyObject *o, PyObject *key)

   Return element of *o* corresponding to the object *key* or ``NULL`` on failure.
   This is the equivalent of the Python expression ``o[key]``.


.. c:function:: int PyObject_SetItem(PyObject *o, PyObject *key, PyObject *v)

   Map the object *key* to the value *v*.  Raise an exception and
   return ``-1`` on failure; return ``0`` on success.  This is the
   equivalent of the Python statement ``o[key] = v``.  This function *does
   not* steal a reference to *v*.


.. c:function:: int PyObject_DelItem(PyObject *o, PyObject *key)

   Remove the mapping for the object *key* from the object *o*.  Return ``-1``
   on failure.  This is equivalent to the Python statement ``del o[key]``.


.. c:function:: int PyObject_DelItemString(PyObject *o, const char *key)

   This is the same as :c:func:`PyObject_DelItem`, but *key* is
   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
   rather than a :c:expr:`PyObject*`.


.. c:function:: PyObject* PyObject_Dir(PyObject *o)

   This is equivalent to the Python expression ``dir(o)``, returning a (possibly
   empty) list of strings appropriate for the object argument, or ``NULL`` if there
   was an error.  If the argument is ``NULL``, this is like the Python ``dir()``,
   returning the names of the current locals; in this case, if no execution frame
   is active then ``NULL`` is returned but :c:func:`PyErr_Occurred` will return false.


.. c:function:: PyObject* PyObject_GetIter(PyObject *o)

   This is equivalent to the Python expression ``iter(o)``. It returns a new
   iterator for the object argument, or the object  itself if the object is already
   an iterator.  Raises :exc:`TypeError` and returns ``NULL`` if the object cannot be
   iterated.


.. c:function:: PyObject* PyObject_SelfIter(PyObject *obj)

   This is equivalent to the Python ``__iter__(self): return self`` method.
   It is intended for :term:`iterator` types, to be used in the :c:member:`PyTypeObject.tp_iter` slot.


.. c:function:: PyObject* PyObject_GetAIter(PyObject *o)

   This is the equivalent to the Python expression ``aiter(o)``. Takes an
   :class:`AsyncIterable` object and returns an :class:`AsyncIterator` for it.
   This is typically a new iterator but if the argument is an
   :class:`AsyncIterator`, this returns itself. Raises :exc:`TypeError` and
   returns ``NULL`` if the object cannot be iterated.

   .. versionadded:: 3.10

.. c:function:: void *PyObject_GetTypeData(PyObject *o, PyTypeObject *cls)

   Get a pointer to subclass-specific data reserved for *cls*.

   The object *o* must be an instance of *cls*, and *cls* must have been
   created using negative :c:member:`PyType_Spec.basicsize`.
   Python does not check this.

   On error, set an exception and return ``NULL``.

   .. versionadded:: 3.12

.. c:function:: Py_ssize_t PyType_GetTypeDataSize(PyTypeObject *cls)

   Return the size of the instance memory space reserved for *cls*, i.e. the size of the
   memory :c:func:`PyObject_GetTypeData` returns.

   This may be larger than requested using :c:member:`-PyType_Spec.basicsize <PyType_Spec.basicsize>`;
   it is safe to use this larger size (e.g. with :c:func:`!memset`).

   The type *cls* **must** have been created using
   negative :c:member:`PyType_Spec.basicsize`.
   Python does not check this.

   On error, set an exception and return a negative value.

   .. versionadded:: 3.12

.. c:function:: void *PyObject_GetItemData(PyObject *o)

   Get a pointer to per-item data for a class with
   :c:macro:`Py_TPFLAGS_ITEMS_AT_END`.

   On error, set an exception and return ``NULL``.
   :py:exc:`TypeError` is raised if *o* does not have
   :c:macro:`Py_TPFLAGS_ITEMS_AT_END` set.

   .. versionadded:: 3.12

.. c:function:: int PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg)

   Visit the managed dictionary of *obj*.

   This function must only be called in a traverse function of the type which
   has the :c:macro:`Py_TPFLAGS_MANAGED_DICT` flag set.

   .. versionadded:: 3.13

.. c:function:: void PyObject_ClearManagedDict(PyObject *obj)

   Clear the managed dictionary of *obj*.

   This function must only be called in a clear function of the type which
   has the :c:macro:`Py_TPFLAGS_MANAGED_DICT` flag set.

   .. versionadded:: 3.13

.. c:function:: int PyUnstable_Object_EnableDeferredRefcount(PyObject *obj)

   Enable `deferred reference counting <https://peps.python.org/pep-0703/#deferred-reference-counting>`_ on *obj*,
   if supported by the runtime.  In the :term:`free-threaded <free threading>` build,
   this allows the interpreter to avoid reference count adjustments to *obj*,
   which may improve multi-threaded performance.  The tradeoff is
   that *obj* will only be deallocated by the tracing garbage collector, and
   not when the interpreter no longer has any references to it.

   This function returns ``1`` if deferred reference counting is enabled on *obj*,
   and ``0`` if deferred reference counting is not supported or if the hint was
   ignored by the interpreter, such as when deferred reference counting is already
   enabled on *obj*. This function is thread-safe, and cannot fail.

   This function does nothing on builds with the :term:`GIL` enabled, which do
   not support deferred reference counting. This also does nothing if *obj* is not
   an object tracked by the garbage collector (see :func:`gc.is_tracked` and
   :c:func:`PyObject_GC_IsTracked`).

   This function is intended to be used soon after *obj* is created,
   by the code that creates it, such as in the object's :c:member:`~PyTypeObject.tp_new`
   slot.

   .. versionadded:: 3.14

.. c:function:: int PyUnstable_Object_IsUniqueReferencedTemporary(PyObject *obj)

   Check if *obj* is a unique temporary object.
   Returns ``1`` if *obj* is known to be a unique temporary object,
   and ``0`` otherwise.  This function cannot fail, but the check is
   conservative, and may return ``0`` in some cases even if *obj* is a unique
   temporary object.

   If an object is a unique temporary, it is guaranteed that the current code
   has the only reference to the object. For arguments to C functions, this
   should be used instead of checking if the reference count is ``1``. Starting
   with Python 3.14, the interpreter internally avoids some reference count
   modifications when loading objects onto the operands stack by
   :term:`borrowing <borrowed reference>` references when possible, which means
   that a reference count of ``1`` by itself does not guarantee that a function
   argument uniquely referenced.

   In the example below, ``my_func`` is called with a unique temporary object
   as its argument::

      my_func([1, 2, 3])

   In the example below, ``my_func`` is **not** called with a unique temporary
   object as its argument, even if its refcount is ``1``::

      my_list = [1, 2, 3]
      my_func(my_list)

   See also the function :c:func:`Py_REFCNT`.

   .. versionadded:: 3.14

.. c:function:: int PyUnstable_IsImmortal(PyObject *obj)

   This function returns non-zero if *obj* is :term:`immortal`, and zero
   otherwise. This function cannot fail.

   .. note::

      Objects that are immortal in one CPython version are not guaranteed to
      be immortal in another.

   .. versionadded:: 3.14

.. c:function:: int PyUnstable_TryIncRef(PyObject *obj)

   Increments the reference count of *obj* if it is not zero.  Returns ``1``
   if the object's reference count was successfully incremented. Otherwise,
   this function returns ``0``.

   :c:func:`PyUnstable_EnableTryIncRef` must have been called
   earlier on *obj* or this function may spuriously return ``0`` in the
   :term:`free-threaded build`.

   This function is logically equivalent to the following C code, except that
   it behaves atomically in the :term:`free-threaded build`::

      if (Py_REFCNT(op) > 0) {
         Py_INCREF(op);
         return 1;
      }
      return 0;

   This is intended as a building block for managing weak references
   without the overhead of a Python :ref:`weak reference object <weakrefobjects>`.

   Typically, correct use of this function requires support from *obj*'s
   deallocator (:c:member:`~PyTypeObject.tp_dealloc`).
   For example, the following sketch could be adapted to implement a
   "weakmap" that works like a :py:class:`~weakref.WeakValueDictionary`
   for a specific type:

   .. code-block:: c

      PyMutex mutex;

      PyObject *
      add_entry(weakmap_key_type *key, PyObject *value)
      {
          PyUnstable_EnableTryIncRef(value);
          weakmap_type weakmap = ...;
          PyMutex_Lock(&mutex);
          weakmap_add_entry(weakmap, key, value);
          PyMutex_Unlock(&mutex);
          Py_RETURN_NONE;
      }

      PyObject *
      get_value(weakmap_key_type *key)
      {
          weakmap_type weakmap = ...;
          PyMutex_Lock(&mutex);
          PyObject *result = weakmap_find(weakmap, key);
          if (PyUnstable_TryIncRef(result)) {
              // `result` is safe to use
              PyMutex_Unlock(&mutex);
              return result;
          }
          // if we get here, `result` is starting to be garbage-collected,
          // but has not been removed from the weakmap yet
          PyMutex_Unlock(&mutex);
          return NULL;
      }

      // tp_dealloc function for weakmap values
      void
      value_dealloc(PyObject *value)
      {
          weakmap_type weakmap = ...;
          PyMutex_Lock(&mutex);
          weakmap_remove_value(weakmap, value);

          ...
          PyMutex_Unlock(&mutex);
      }

   .. versionadded:: 3.14

.. c:function:: void PyUnstable_EnableTryIncRef(PyObject *obj)

   Enables subsequent uses of :c:func:`PyUnstable_TryIncRef` on *obj*.  The
   caller must hold a :term:`strong reference` to *obj* when calling this.

   .. versionadded:: 3.14

.. c:function:: int PyUnstable_Object_IsUniquelyReferenced(PyObject *op)

   Determine if *op* only has one reference.

   On GIL-enabled builds, this function is equivalent to
   :c:expr:`Py_REFCNT(op) == 1`.

   On a :term:`free-threaded build`, this checks if *op*'s
   :term:`reference count` is equal to one and additionally checks if *op*
   is only used by this thread. :c:expr:`Py_REFCNT(op) == 1` is **not**
   thread-safe on free-threaded builds; prefer this function.

   The caller must hold an :term:`attached thread state`, despite the fact
   that this function doesn't call into the Python interpreter. This function
   cannot fail.

   .. versionadded:: 3.14

.. c:function:: int PyUnstable_SetImmortal(PyObject *op)

   Marks the object *op* :term:`immortal`. The argument should be uniquely referenced by
   the calling thread. This is intended to be used for reducing reference counting contention
   in the :term:`free-threaded build` for objects which are shared across threads.

   This is a one-way process: objects can only be made immortal; they cannot be
   made mortal once again. Immortal objects do not participate in reference counting
   and will never be garbage collected. If the object is GC-tracked, it is untracked.

   This function is intended to be used soon after *op* is created, by the code that
   creates it, such as in the object's :c:member:`~PyTypeObject.tp_new` slot.
   Returns 1 if the object was made immortal and returns 0 if it was not.
   This function cannot fail.

   .. versionadded:: 3.15
