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[3.10] gh-99249: Clarify "read-only" slots tp_bases & tp_mro (GH-99342) #99838

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Nov 28, 2022
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[3.10] gh-99249: Clarify "read-only" slots tp_bases & tp_mro (GH-99342) #99838

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31 changes: 25 additions & 6 deletions Doc/c-api/typeobj.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -149,10 +149,16 @@ Quick Reference
+------------------------------------------------+-----------------------------------+-------------------+---+---+---+---+

.. [#slots]
A slot name in parentheses indicates it is (effectively) deprecated.
Names in angle brackets should be treated as read-only.
Names in square brackets are for internal use only.
"<R>" (as a prefix) means the field is required (must be non-``NULL``).

**()**: A slot name in parentheses indicates it is (effectively) deprecated.

**<>**: Names in angle brackets should be initially set to ``NULL`` and
treated as read-only.

**[]**: Names in square brackets are for internal use only.

**<R>** (as a prefix) means the field is required (must be non-``NULL``).

.. [#cols] Columns:

**"O"**: set on :c:type:`PyBaseObject_Type`
Expand Down Expand Up @@ -1909,8 +1915,19 @@ and :c:type:`PyType_Type` effectively act as defaults.)

Tuple of base types.

This is set for types created by a class statement. It should be ``NULL`` for
statically defined types.
This field should be set to ``NULL`` and treated as read-only.
Python will fill it in when the type is :c:func:`initialized <PyType_Ready>`.

For dynamically created classes, the ``Py_tp_bases``
:c:type:`slot <PyType_Slot>` can be used instead of the *bases* argument
of :c:func:`PyType_FromSpecWithBases`.
The argument form is preferred.

.. warning::

Multiple inheritance does not work well for statically defined types.
If you set ``tp_bases`` to a tuple, Python will not raise an error,
but some slots will only be inherited from the first base.

**Inheritance:**

Expand All @@ -1922,6 +1939,8 @@ and :c:type:`PyType_Type` effectively act as defaults.)
Tuple containing the expanded set of base types, starting with the type itself
and ending with :class:`object`, in Method Resolution Order.

This field should be set to ``NULL`` and treated as read-only.
Python will fill it in when the type is :c:func:`initialized <PyType_Ready>`.

**Inheritance:**

Expand Down