Document __base__ attribute in data model reference

Author: furkanonder

Doc/c-api/object.rst

@@ -392,17 +392,6 @@ Object Protocol
    class, are considered classes.  However, objects can override this by having
    a :attr:`~type.__bases__` attribute (which must be a tuple of base classes).
 
-   Another attribute, ``__base__`` corresponds to the :c:member:`~PyTypeObject.tp_base`
-   in a type object. At the C level, Python has a single inheritance model
-   that determines the memory layout of instances. There is a chain involving
-   base classes that contribute to the instance layout. ``__base__`` is the base
-   class that is involved in that chain. When such a class takes arguments in
-   the correct order, then starting leftmost.
-
-   .. impl-detail::
-      Note that behavior of the ``__base__`` attribute is dependent on the
-      :term:`CPython` implementation.
-
 
 .. c:function:: int PyObject_IsInstance(PyObject *inst, PyObject *cls)
 

Doc/reference/datamodel.rst

@@ -1185,6 +1185,7 @@ Special attributes
    single: __module__ (class attribute)
    single: __dict__ (class attribute)
    single: __bases__ (class attribute)
+   single: __base__ (class attribute)
    single: __doc__ (class attribute)
    single: __annotations__ (class attribute)
    single: __annotate__ (class attribute)
@@ -1219,6 +1220,16 @@ Special attributes
        In most cases, for a class defined as ``class X(A, B, C)``,
        ``X.__bases__`` will be exactly equal to ``(A, B, C)``.
 
+   * - .. attribute:: type.__base__
+     - The base class that determines the instance layout. This attribute
+       identifies the single base class in the inheritance chain that is
+       responsible for the memory layout of instances, corresponding to
+       :c:member:`~PyTypeObject.tp_base` at the C level.
+
+       .. impl-detail::
+          Note that behavior of the ``__base__`` attribute is dependent on the
+          :term:`CPython` implementation.
+
    * - .. attribute:: type.__doc__
      - The class's documentation string, or ``None`` if undefined.
        Not inherited by subclasses.