From ebaf0945f9f630f32755137a54abd0a49f068e9a Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <rhettinger@users.noreply.github.com>
Date: Fri, 6 May 2022 02:57:53 -0500
Subject: [PATCH] GH-89519: Deprecate classmethod descriptor chaining (#92379)
---
Doc/howto/descriptor.rst | 4 +++-
Doc/library/functions.rst | 5 +++++
Doc/whatsnew/3.11.rst | 8 ++++++++
.../2022-05-06-02-29-53.gh-issue-89519.4OfkRE.rst | 4 ++++
4 files changed, 20 insertions(+), 1 deletion(-)
create mode 100644 Misc/NEWS.d/next/Core and Builtins/2022-05-06-02-29-53.gh-issue-89519.4OfkRE.rst
diff --git a/Doc/howto/descriptor.rst b/Doc/howto/descriptor.rst
index 825e9d0347f..5e9b110f0fe 100644
--- a/Doc/howto/descriptor.rst
+++ b/Doc/howto/descriptor.rst
@@ -1349,6 +1349,8 @@ Using the non-data descriptor protocol, a pure Python version of
if cls is None:
cls = type(obj)
if hasattr(type(self.f), '__get__'):
+ # This code path was added in Python 3.9
+ # and was deprecated in Python 3.11.
return self.f.__get__(cls, cls)
return MethodType(self.f, cls)
@@ -1386,7 +1388,7 @@ Using the non-data descriptor protocol, a pure Python version of
The code path for ``hasattr(type(self.f), '__get__')`` was added in
Python 3.9 and makes it possible for :func:`classmethod` to support
chained decorators. For example, a classmethod and property could be
-chained together:
+chained together. In Python 3.11, this functionality was deprecated.
.. testcode::
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index cb862968970..47b4b11cced 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -271,6 +271,11 @@ are always available. They are listed here in alphabetical order.
``__name__``, ``__qualname__``, ``__doc__`` and ``__annotations__``) and
have a new ``__wrapped__`` attribute.
+ .. versionchanged:: 3.11
+ Class methods can no longer wrap other :term:`descriptors <descriptor>` such as
+ :func:`property`.
+
+
.. function:: compile(source, filename, mode, flags=0, dont_inherit=False, optimize=-1)
Compile the *source* into a code or AST object. Code objects can be executed
diff --git a/Doc/whatsnew/3.11.rst b/Doc/whatsnew/3.11.rst
index 822cb8b1f0f..19ac8676ba6 100644
--- a/Doc/whatsnew/3.11.rst
+++ b/Doc/whatsnew/3.11.rst
@@ -1084,6 +1084,14 @@ CPython bytecode changes
Deprecated
==========
+* Chaining :class:`classmethod` descriptors (introduced in :issue:`19072`)
+ is now deprecated. It can no longer be used to wrap other descriptors
+ such as :class:`property`. The core design of this feature was flawed
+ and caused a number of downstream problems. To "pass-through" a
+ :class:`classmethod`, consider using the ``__wrapped__`` attribute
+ that was added in Python 3.10.
+ (Contributed by Raymond Hettinger in :gh:`89519`.)
+
* Octal escapes with value larger than ``0o377`` now produce
a :exc:`DeprecationWarning`.
In a future Python version they will be a :exc:`SyntaxWarning` and
diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-05-06-02-29-53.gh-issue-89519.4OfkRE.rst b/Misc/NEWS.d/next/Core and Builtins/2022-05-06-02-29-53.gh-issue-89519.4OfkRE.rst
new file mode 100644
index 00000000000..1460546d148
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2022-05-06-02-29-53.gh-issue-89519.4OfkRE.rst
@@ -0,0 +1,4 @@
+Chaining classmethod descriptors (introduced in bpo-19072) is deprecated. It
+can no longer be used to wrap other descriptors such as property(). The
+core design of this feature was flawed, and it caused a number of downstream
+problems.
--
GitLab