.. 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 function would 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:: 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 are silently ignored.
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.
.. 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 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.
.. 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:: 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_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 traverse 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.
This function returns ``1`` if deferred reference counting is enabled on *obj*
(including when it was enabled before the call),
and ``0`` if deferred reference counting is not supported or if the hint was
ignored by the runtime. 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.
.. versionadded:: 3.14
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