Issue #25701: Document C API functions that both set and delete objects
Also document that the separate functions that delete objects are preferred;
using PyObject_SetAttr(), _SetAttrString(), and PySequence_SetItem() to
delete is deprecated.
diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index 97b45b1..b761c80 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -68,25 +68,35 @@
.. 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*. Returns ``-1`` on failure. This is the equivalent of the Python statement
+ *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, however this feature is
+ deprecated in favour of using :c:func:`PyObject_DelAttr`.
+
.. c:function:: int PyObject_SetAttrString(PyObject *o, const char *attr_name, PyObject *v)
Set the value of the attribute named *attr_name*, for object *o*, to the value
- *v*. Returns ``-1`` on failure. This is the equivalent of the Python statement
+ *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, however this feature is
+ deprecated in favour of using :c:func:`PyObject_DelAttrString`.
+
.. c:function:: int PyObject_GenericSetAttr(PyObject *o, PyObject *name, PyObject *value)
- Generic attribute setter function that is meant to be put into a type
- object's ``tp_setattro`` slot. It looks for a data descriptor in the
+ 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 the attribute in the instance dictionary. Otherwise, the
- attribute is set in the object's :attr:`~object.__dict__` (if present).
- Otherwise, an :exc:`AttributeError` is raised and ``-1`` is returned.
+ 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)
@@ -378,7 +388,8 @@
.. c:function:: int PyObject_SetItem(PyObject *o, PyObject *key, PyObject *v)
- Map the object *key* to the value *v*. Returns ``-1`` on failure. This is the
+ 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``.
diff --git a/Doc/c-api/sequence.rst b/Doc/c-api/sequence.rst
index 5960db9..f1825f0 100644
--- a/Doc/c-api/sequence.rst
+++ b/Doc/c-api/sequence.rst
@@ -62,10 +62,14 @@
.. c:function:: int PySequence_SetItem(PyObject *o, Py_ssize_t i, PyObject *v)
- Assign object *v* to the *i*\ th element of *o*. Returns ``-1`` on failure. This
+ Assign object *v* to the *i*\ th element of *o*. Raise an exception
+ and return ``-1`` on failure; return ``0`` on success. This
is the equivalent of the Python statement ``o[i] = v``. This function *does
not* steal a reference to *v*.
+ If *v* is *NULL*, the element is deleted, however this feature is
+ deprecated in favour of using :c:func:`PySequence_DelItem`.
+
.. c:function:: int PySequence_DelItem(PyObject *o, Py_ssize_t i)
diff --git a/Doc/c-api/typeobj.rst b/Doc/c-api/typeobj.rst
index b5113aa..ac589b8 100644
--- a/Doc/c-api/typeobj.rst
+++ b/Doc/c-api/typeobj.rst
@@ -208,12 +208,13 @@
.. c:member:: setattrfunc PyTypeObject.tp_setattr
- An optional pointer to the set-attribute-string function.
+ An optional pointer to the function for setting and deleting attributes.
This field is deprecated. When it is defined, it should point to a function
that acts the same as the :c:member:`~PyTypeObject.tp_setattro` function, but taking a C string
instead of a Python string object to give the attribute name. The signature is
- the same as for :c:func:`PyObject_SetAttrString`.
+ the same as for :c:func:`PyObject_SetAttrString`, but setting
+ *v* to *NULL* to delete an attribute must be supported.
This field is inherited by subtypes together with :c:member:`~PyTypeObject.tp_setattro`: a subtype
inherits both :c:member:`~PyTypeObject.tp_setattr` and :c:member:`~PyTypeObject.tp_setattro` from its base type when
@@ -351,9 +352,10 @@
.. c:member:: setattrofunc PyTypeObject.tp_setattro
- An optional pointer to the set-attribute function.
+ An optional pointer to the function for setting and deleting attributes.
- The signature is the same as for :c:func:`PyObject_SetAttr`. It is usually
+ The signature is the same as for :c:func:`PyObject_SetAttr`, but setting
+ *v* to *NULL* to delete an attribute must be supported. It is usually
convenient to set this field to :c:func:`PyObject_GenericSetAttr`, which
implements the normal way of setting object attributes.
@@ -724,7 +726,7 @@
typedef struct PyGetSetDef {
char *name; /* attribute name */
getter get; /* C function to get the attribute */
- setter set; /* C function to set the attribute */
+ setter set; /* C function to set or delete the attribute */
char *doc; /* optional doc string */
void *closure; /* optional additional data for getter and setter */
} PyGetSetDef;
@@ -775,12 +777,14 @@
.. c:member:: descrsetfunc PyTypeObject.tp_descr_set
- An optional pointer to a "descriptor set" function.
+ An optional pointer to a function for setting and deleting
+ a descriptor's value.
The function signature is ::
int tp_descr_set(PyObject *self, PyObject *obj, PyObject *value);
+ The *value* argument is set to *NULL* to delete the value.
This field is inherited by subtypes.
.. XXX explain.
@@ -1171,9 +1175,11 @@
.. c:member:: objobjargproc PyMappingMethods.mp_ass_subscript
- This function is used by :c:func:`PyObject_SetItem` and has the same
- signature. If this slot is *NULL*, the object does not support item
- assignment.
+ This function is used by :c:func:`PyObject_SetItem` and
+ :c:func:`PyObject_DelItem`. It has the same signature as
+ :c:func:`PyObject_SetItem`, but *v* can also be set to *NULL* to delete
+ an item. If this slot is *NULL*, the object does not support item
+ assignment and deletion.
.. _sequence-structs:
@@ -1222,7 +1228,7 @@
This function is used by :c:func:`PySequence_SetItem` and has the same
signature. This slot may be left to *NULL* if the object does not support
- item assignment.
+ item assignment and deletion.
.. c:member:: objobjproc PySequenceMethods.sq_contains