[3.8] [3.9] bpo-41688: Document bug in **= dispatching in the language data… (GH...

(cherry picked from commit 46bc21e1780016aaacd34e472f838dc792fb674c)

Co-authored-by: Ammar Askar <ammar@ammaraskar.com>
Automerge-Triggered-By: @brettcannon

diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index c1262cdb9c106025626276813677e8e6f457b99d..3f053858624164bc6d5efcba90272fb2a15f5e41 100644 (file)
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -2404,6 +2404,13 @@ left undefined.
    :ref:`faq-augmented-assignment-tuple-error`), but this behavior is in fact
    part of the data model.
 
+   .. note::
+
+      Due to a bug in the dispatching mechanism for ``**=``, a class that
+      defines :meth:`__ipow__` but returns ``NotImplemented`` would fail to
+      fall back to ``x.__pow__(y)`` and ``y.__rpow__(x)``. This bug is fixed
+      in Python 3.10.
+
 
 .. method:: object.__neg__(self)
             object.__pos__(self)