Description

brianschubert

opened on Apr 6, 2025

Issue body actions

Feature or enhancement

Proposal:

ctypes.py_object is generic in typeshed, but is not subscriptable at runtime. This can be troublesome for end users, since type checkers will prompt them to supply a generic type argument, but doing so will produce a TypeError at runtime:

>>> import ctypes
>>> ctypes.py_object[int]
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    ctypes.py_object[int]
    ~~~~~~~~~~~~~~~~^^^^^
TypeError: type 'py_object' is not subscriptable

(albeit this is partially mitigated by deferred annotations in 3.14, but TypeError can still pop up if the annotations are ever evaluated)

py_object's typeshed stubs have been stable for a while, and it seems unlikely to be made non-generic in the future. Therefore I propose that __class_getitem__ be added to ctypes.py_object so that it can be subscripted at runtime.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

python/typeshed#13760

Linked PRs

• gh-132168: Add __class_getitem__ to ctypes.py_object #132169

Reacted by Joren Hammudoglu

Activity

1. brianschubert

   added

   type-featureA feature request or enhancementA feature request or enhancement

   on Apr 6, 2025
2. tomasr8

   added this to Ctypes issueson Apr 6, 2025
3. tomasr8

   added

   extension-modulesC modules in the Modules dirC modules in the Modules dir

   topic-ctypes

   topic-typing

   on Apr 6, 2025
4. picnixz commented on Apr 6, 2025

   

   picnixz

   on Apr 6, 2025

   Member

   More actions

   What's the reason for having ctypes.py_object generic actually? what does ctypes.py_object[int] means? does it mean a PyLongObject?
5. sobolevn commented on Apr 6, 2025

   

   sobolevn

   on Apr 6, 2025

   Member

   More actions

   @picnixz see https://github.com/python/typeshed/blob/2b7019b933ac8339e4ae8f4619a2a746446a8532/stdlib/ctypes/__init__.pyi#L253

   Reacted by Bénédikt Tran
6. brianschubert commented on Apr 6, 2025

   

   brianschubert

   on Apr 6, 2025

   ContributorAuthor

   More actions

   It represents a pointer to an arbitrary Python object. Having it be generic lets you statically track the type of that object. I haven't written enough ctypes code to personally need it, but I imagine it being generic is useful if you need to access py_object.value, or if you need to type-hint a function whose behavior depends on the type of object that py_object is holding. It being generic also seems to be useful to numpy.
7. AA-Turner

   added a commit that references this issue on Apr 6, 2025

   gh-132168: Add `__class_getitem__` to `ctypes.py_object` (#132169)

   e247639
8. picnixz

   closed this as completedon Apr 6, 2025
9. github-project-automation

   moved this to Done in Ctypes issueson Apr 6, 2025

Issue actions