Improve some C API documentation (GH-108768)

* Express functions which take argument as a C string in terms of
  functions which take Python object.
* Use "note" directive for PyMapping_HasKey() and
  PyMapping_HasKeyString() notes.

Doc/c-api/dict.rst

@@ -79,12 +79,9 @@ Dictionary Objects
 
 .. c:function:: int PyDict_SetItemString(PyObject *p, const char *key, PyObject *val)
 
-   .. index:: single: PyUnicode_FromString()
-
-   Insert *val* into the dictionary *p* using *key* as a key. *key* should
-   be a :c:expr:`const char*` UTF-8 encoded bytes string.  The key object is created using
-   ``PyUnicode_FromString(key)``.  Return ``0`` on success or ``-1`` on
-   failure.  This function *does not* steal a reference to *val*.
+   This is the same as :c:func:`PyDict_SetItem`, but *key* is
+   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
+   rather than a :c:expr:`PyObject*`.
 
 
 .. c:function:: int PyDict_DelItem(PyObject *p, PyObject *key)
@@ -97,10 +94,9 @@ Dictionary Objects
 
 .. c:function:: int PyDict_DelItemString(PyObject *p, const char *key)
 
-   Remove the entry in dictionary *p* which has a key specified by the UTF-8
-   encoded bytes string *key*.
-   If *key* is not in the dictionary, :exc:`KeyError` is raised.
-   Return ``0`` on success or ``-1`` on failure.
+   This is the same as :c:func:`PyDict_DelItem`, but *key* is
+   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
+   rather than a :c:expr:`PyObject*`.
 
 
 .. c:function:: int PyDict_GetItemRef(PyObject *p, PyObject *key, PyObject **result)

Doc/c-api/mapping.rst

@@ -28,9 +28,9 @@ See also :c:func:`PyObject_GetItem`, :c:func:`PyObject_SetItem` and
 
 .. c:function:: PyObject* PyMapping_GetItemString(PyObject *o, const char *key)
 
-   Return element of *o* corresponding to the string *key* or ``NULL`` on failure.
-   This is the equivalent of the Python expression ``o[key]``.
-   See also :c:func:`PyObject_GetItem`.
+   This is the same as :c:func:`PyObject_GetItem`, but *key* is
+   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
+   rather than a :c:expr:`PyObject*`.
 
 
 .. c:function:: int PyMapping_GetOptionalItem(PyObject *obj, PyObject *key, PyObject **result)
@@ -50,38 +50,30 @@ See also :c:func:`PyObject_GetItem`, :c:func:`PyObject_SetItem` and
 
 .. c:function:: int PyMapping_GetOptionalItemString(PyObject *obj, const char *key, PyObject **result)
 
-   Variant of :c:func:`PyMapping_GetItemString` which doesn't raise
-   :exc:`KeyError` if the key is not found.
-
-   If the key is found, return ``1`` and set *\*result* to a new
-   :term:`strong reference` to the corresponding value.
-   If the key is not found, return ``0`` and set *\*result* to ``NULL``;
-   the :exc:`KeyError` is silenced.
-   If an error other than :exc:`KeyError` is raised, return ``-1`` and
-   set *\*result* to ``NULL``.
+   This is the same as :c:func:`PyMapping_GetOptionalItem`, but *key* 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 PyMapping_SetItemString(PyObject *o, const char *key, PyObject *v)
 
-   Map the string *key* to the value *v* in object *o*.  Returns ``-1`` on
-   failure.  This is the equivalent of the Python statement ``o[key] = v``.
-   See also :c:func:`PyObject_SetItem`.  This function *does not* steal a
-   reference to *v*.
+   This is the same as :c:func:`PyObject_SetItem`, but *key* is
+   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
+   rather than a :c:expr:`PyObject*`.
 
 
 .. c:function:: int PyMapping_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]``.
    This is an alias of :c:func:`PyObject_DelItem`.
 
 
 .. c:function:: int PyMapping_DelItemString(PyObject *o, const char *key)
 
-   Remove the mapping for the string *key* from the object *o*.  Return ``-1``
-   on failure.  This is equivalent to the Python statement ``del o[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:: int PyMapping_HasKey(PyObject *o, PyObject *key)
@@ -90,20 +82,27 @@ See also :c:func:`PyObject_GetItem`, :c:func:`PyObject_SetItem` and
    This is equivalent to the Python expression ``key in o``.
    This function always succeeds.
 
-   Note that exceptions which occur while calling the :meth:`~object.__getitem__`
-   method will get suppressed.
-   To get error reporting use :c:func:`PyObject_GetItem()` instead.
+   .. note::
+
+      Exceptions which occur when this calls :meth:`~object.__getitem__`
+      method are silently ignored.
+      For proper error handling, use :c:func:`PyMapping_GetOptionalItem` or
+      :c:func:`PyObject_GetItem()` instead.
 
 
 .. c:function:: int PyMapping_HasKeyString(PyObject *o, const char *key)
 
-   Return ``1`` if the mapping object has the key *key* and ``0`` otherwise.
-   This is equivalent to the Python expression ``key in o``.
-   This function always succeeds.
+   This is the same as :c:func:`PyMapping_HasKey`, but *key* is
+   specified as a :c:expr:`const char*` UTF-8 encoded bytes string,
+   rather than a :c:expr:`PyObject*`.
+
+   .. note::
 
-   Note that exceptions which occur while calling the :meth:`~object.__getitem__`
-   method and creating a temporary string object will get suppressed.
-   To get error reporting use :c:func:`PyMapping_GetItemString()` instead.
+      Exceptions that occur when this calls :meth:`~object.__getitem__`
+      method or while creating the temporary :class:`str`
+      object are silently ignored.
+      For proper error handling, use :c:func:`PyMapping_GetOptionalItemString` or
+      :c:func:`PyMapping_GetItemString` instead.
 
 
 .. c:function:: PyObject* PyMapping_Keys(PyObject *o)

Doc/c-api/object.rst

@@ -43,15 +43,15 @@ Object Protocol
 
 .. c:function:: int PyObject_HasAttrString(PyObject *o, const char *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)``.  This function
-   always succeeds.
+   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.
+      :meth:`~object.__getattribute__` methods or while creating the temporary
+      :class:`str` object are silently ignored.
       For proper error handling, use :c:func:`PyObject_GetOptionalAttrString`
       or :c:func:`PyObject_GetAttrString` instead.
 
@@ -68,9 +68,9 @@ Object Protocol
 
 .. c:function:: PyObject* PyObject_GetAttrString(PyObject *o, const char *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``.
+   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.
@@ -93,15 +93,9 @@ Object Protocol
 
 .. c:function:: int PyObject_GetOptionalAttrString(PyObject *obj, const char *attr_name, PyObject **result);
 
-   Variant of :c:func:`PyObject_GetAttrString` 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``.
+   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
 
@@ -129,10 +123,9 @@ Object Protocol
 
 .. 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*. Raise an exception and return ``-1`` on failure;
-   return ``0`` on success.  This is the equivalent of the Python statement
-   ``o.attr_name = 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`.
@@ -158,8 +151,9 @@ Object Protocol
 
 .. c:function:: int PyObject_DelAttrString(PyObject *o, const char *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``.
+   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*`.
 
 
 .. c:function:: PyObject* PyObject_GenericGetDict(PyObject *o, void *context)