Python 3.12 segfault with mixin classes

[Phil Thompson]

On 15/06/2023 19:03, Florian Bruhin wrote:
> Hey,
> 
>> When trying PyQt 6.5.1 with Python 3.12 Beta 2, something like:
>> 
>>         import sys
>>         from PyQt6.QtWidgets import QWidget, QApplication
>> 
>>         class Mixin: pass
>>         class Command(Mixin, QWidget): pass
>> 
>>         app = QApplication(sys.argv)
>>         cmd = Command()
>>         cmd.show()
>>         app.exec()
>> 
>> segfaults here on the "cmd.Command()" line:
>> 
>>         #0  [...] _PyDict_Next (op=0x0, [...])
>>         [...]
>>         #2  [...]  in trawl_hierarchy([...])
>>            from .../lib/python3.12/site-packages/PyQt6/QtCore.abi3.so
>>         [...]
> 
> Eric Snow commented on the issue:
> 
>     Presumably the crashing code is trying to use the dict returned by
>     sipPyTypeDict() and I'm guessing that that function basically 
> returns
>     pytype->tp_dict and that the pytype in question is a static builtin
>     type. If that's the case then the failure makes sense since tp_dict 
> for
>     static builtin types is now NULL.
> 
> And that indeed seems to be the case: trawl_type does
> "dict = sipPyTypeDict(pytype);", that is an alias to sip's
> api_py_type_dict, and that accesses py_type->tp_dict.
> 
> See:
> https://github.com/python/cpython/issues/105227
> 
> There is now an open PR to add a PyType_GetDict():
> https://github.com/python/cpython/pull/105747

Hopefully fixed in tonight's snapshot - although it needs the next beta 
release of Python v3.12 to build.

Phil