[3.13] gh-120381: Fix inspect.ismethoddescriptor() (GH-120684)

The `inspect.ismethoddescriptor()` function did not check for the lack of
`__delete__()` and, consequently, erroneously returned True when applied
to *data* descriptors with only `__get__()` and `__delete__()` defined.

(cherry picked from commit dacc5ac71a8e546f9ef76805827cb50d4d40cabf)

Co-authored-by: Jan Kaliszewski <zuo@kaliszewski.net>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/Doc/library/inspect.rst b/Doc/library/inspect.rst
index 7130faa..0ec7d7c 100644
--- a/Doc/library/inspect.rst
+++ b/Doc/library/inspect.rst
@@ -504,9 +504,9 @@ attributes (see :ref:`import-mod-attrs` for module attributes):
    are true.
 
    This, for example, is true of ``int.__add__``.  An object passing this test
-   has a :meth:`~object.__get__` method but not a :meth:`~object.__set__`
-   method, but beyond that the set of attributes varies.  A
-   :attr:`~definition.__name__` attribute is usually
+   has a :meth:`~object.__get__` method, but not a :meth:`~object.__set__`
+   method or a :meth:`~object.__delete__` method.  Beyond that, the set of
+   attributes varies.  A :attr:`~definition.__name__` attribute is usually
    sensible, and :attr:`!__doc__` often is.
 
    Methods implemented via descriptors that also pass one of the other tests
@@ -515,6 +515,11 @@ attributes (see :ref:`import-mod-attrs` for module attributes):
    :attr:`~method.__func__` attribute (etc) when an object passes
    :func:`ismethod`.
 
+   .. versionchanged:: 3.13
+      This function no longer incorrectly reports objects with :meth:`~object.__get__`
+      and :meth:`~object.__delete__`, but not :meth:`~object.__set__`, as being method
+      descriptors (such objects are data descriptors, not method descriptors).
+
 
 .. function:: isdatadescriptor(object)