From 219696abb240607d3f807853c4c180825e60716e Mon Sep 17 00:00:00 2001
From: Petr Viktorin <encukou@gmail.com>
Date: Mon, 28 Nov 2022 09:22:08 +0100
Subject: [PATCH] gh-99249: Clarify "read-only" slots tp_bases & tp_mro
(GH-99342)
These slots are marked "should be treated as read-only" in the
table at the start of the document. That doesn't say anything about
setting them in the static struct.
`tp_bases` docs did say that it should be ``NULL`` (TIL!). If you
ignore that, seemingly nothing bad happens. However, some slots
may not be inherited, depending on which sub-slot structs are present.
(FWIW, NumPy sets tp_bases and is affected by the quirk -- though to
be fair, its DUAL_INHERIT code probably predates tp_bases docs, and
also the result happens to be benign.)
This patch makes things explicit.
It also makes the summary table legend easier to scan.
Co-authored-by: Kumar Aditya <59607654+kumaraditya303@users.noreply.github.com>
---
Doc/c-api/typeobj.rst | 31 +++++++++++++++++++++++++------
1 file changed, 25 insertions(+), 6 deletions(-)
diff --git a/Doc/c-api/typeobj.rst b/Doc/c-api/typeobj.rst
index 4c462f46056..8f8869ec668 100644
--- a/Doc/c-api/typeobj.rst
+++ b/Doc/c-api/typeobj.rst
@@ -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`
@@ -1923,8 +1929,19 @@ 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:**
@@ -1936,6 +1953,8 @@ 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:**
--
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