inspect.ismethoddescriptor(): lack of __delete__() is not checked

[zuo]

Bug report

Bug description:

The inspect.ismethoddescriptor() function reports descriptor objects which implement __delete__() but not __set__() as method descriptors, even though they are, in fact, data descriptors:

Actual behavior example:

>>> import inspect
>>> class Descriptor:
...     def __get__(self, *_): pass
...     def __delete__(self, *_): pass  # Note: `__set__()` *not* defined.
...
>>> inspect.ismethoddescriptor(Descriptor())  # Wrong result:
True

Expected result:

>>> inspect.ismethoddescriptor(Descriptor())  # Correct result:
False

See also: https://discuss.python.org/t/inspect-ismethoddescriptor-checks-for-the-lack-of-set-but-ignores-delete-should-it-be-fixed/55039

---

There is an additional question: to which Python versions should the fix be applied?

IMHO, the fix can be safely applied to the branches 3.14 (main) and 3.13 (still in the beta phase). Backporting it to the earlier versions might be considered too disruptive. Obviously, the decision will need to be made by a core developer, not me.

---

CPython versions tested on:

3.8, 3.9, 3.10, 3.11, 3.12, 3.13, CPython main branch

Linked PRs

• gh-120381: Fix inspect.ismethoddescriptor() #120383
• [3.13] gh-120381: Fix inspect.ismethoddescriptor() (GH-120383) #120684

[ncoghlan]

Merged and fixed for the next 3.13 beta. Thanks for the report and PR, @zuo!

[zuo]

Merged and fixed for the next 3.13 beta. Thanks for the report and PR, @zuo!

Thank you too! :)