PyObjC contains some functionality that needs to walk the entire MRO of classes and access thetp_dict slot. As of Python 3.12 beta 1 this code crashes due to the slot beingNULL on static builtin types.

The code in PyObjC walks the MRO to implementtp_getattro for the proxy of Objective-C classes to replicatePyObject_GenericGetAttr with some customisations, as wel as in the implementation of an alternative tosuper (again with customisations in the attribute resolution path). All code paths only need read-only access to thetp_dict of static builtin types, although some code needs to be able to update thetp_dict of classes created by PyObjC.

There is currently no documented alternative for directly accessingtp_dict, and because of this I've changed PyObjC to use the private API_PyType_GetDict.

Some alternatives I've looked into:

• UsePyObject_GetAttrString(someType, "__dict__"): This increases the complexity of the PyObjC code bases and requires changes to long stable code:

  • Needs to introduce a different code path for accessing the__dict__ slot of non-PyObjC subclasses

  • Needs to switch to the abstract Mapping API instead of the PyDict API, which likely has a performance impact

  • Changes to reference counting invariants in the code

• Use_PyType_GetDict on Python 3.12 or later: This works, but introduces a reliance on a private CPython API that might disappear at any moment (even micro releases), for example by no longer exporting the function from shared libraries.

Proposal: Rename_PyType_GetDict to eitherPyUnstable_Type_GetDict orPyType_GetDict, while keeping the current interface (e.g. returning a borrowed reference and never raising an exception).

This is a follow-up from#105020

@ericsnowcurrently

Linked PRs

• gh-105227: Add PyType_GetDict() #105747
• [3.12] gh-105227: Add PyType_GetDict() (GH-105747) #106600