3.14a7 regression: Segfault with PyQt6 in _Py_TYPE

[The-Compiler]

Crash report

What happened?

With Python 3.14 Alpha 6, PyQt6 seems to work perfectly fine. On Alpha 7, however, a python3 -c "from PyQt6 import QtCore" immediately segfaults:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff75e765e in _Py_TYPE (ob=0xffffffffffffffff) at /usr/include/python3.14/object.h:270
270	       return ob->ob_type;

in:

#0  0x00007ffff75e765e in _Py_TYPE (ob=0xffffffffffffffff) at /usr/include/python3.14/object.h:270
#1  createClassType (client=client@entry=0x7ffff7537a40 <sipModuleAPI_QtCore>, ctd=0x7ffff7509960 <sipTypeDef_QtCore_PyQtMutexLocker>,
    mod_dict=mod_dict@entry=0x7ffff7675670) at [...]/pyqt6-sip_[...]/sip_core.c:5721
#2  0x00007ffff75ee1d3 in sip_api_init_module (client=0x7ffff7537a40 <sipModuleAPI_QtCore>, mod_dict=0x7ffff7675670)
    at [...]/pyqt6-sip_[...]/sip_core.c:1667
#3  0x00007ffff739e960 in PyInit_QtCore () from [...]/python3.14/site-packages/PyQt6/[QtCore.abi3.so](http://qtcore.abi3.so/)
#4  0x00005555558046db in _PyImport_RunModInitFunc (p0=p0@entry=0x7ffff739e820 <PyInit_QtCore>, info=info@entry=0x7fffffffc2c0,
    p_res=p_res@entry=0x7fffffffc230) at ./Python/importdl.c:430

Full traceback

On the current `main` branch, 9634085:

#0  0x00007ffff75e765e in _Py_TYPE (ob=0xffffffffffffffff) at /usr/include/python3.14/object.h:270
#1  createClassType (client=client@entry=0x7ffff7537a40 <sipModuleAPI_QtCore>, ctd=0x7ffff7509960 <sipTypeDef_QtCore_PyQtMutexLocker>, mod_dict=mod_dict@entry=0x7ffff7675910) at /tmp/pip-install-t41fe3xw/pyqt6-sip_d2261e560e79460e8c0f8c7429b3599e/sip_core.c:5721
#2  0x00007ffff75ee1d3 in sip_api_init_module (client=0x7ffff7537a40 <sipModuleAPI_QtCore>, mod_dict=0x7ffff7675910) at /tmp/pip-install-t41fe3xw/pyqt6-sip_d2261e560e79460e8c0f8c7429b3599e/sip_core.c:1667
#3  0x00007ffff739e960 in PyInit_QtCore () from /home/florian/proj/cpython/.venv/lib/python3.14/site-packages/PyQt6/QtCore.abi3.so
#4  0x000055555580581b in _PyImport_RunModInitFunc (p0=p0@entry=0x7ffff739e820 <PyInit_QtCore>, info=info@entry=0x7fffffffc2f0, p_res=p_res@entry=0x7fffffffc260) at ./Python/importdl.c:430
#5  0x000055555580237b in import_run_extension (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, p0=p0@entry=0x7ffff739e820 <PyInit_QtCore>, info=info@entry=0x7fffffffc2f0, spec=spec@entry=0x7ffff76062c0, modules=<optimized out>) at Python/import.c:2003
#6  0x0000555555803051 in _imp_create_dynamic_impl (module=module@entry=0x7ffff7c66f30, spec=0x7ffff76062c0, file=<optimized out>) at Python/import.c:4704
#7  0x00005555558030cf in _imp_create_dynamic (module=0x7ffff7c66f30, args=args@entry=0x7ffff77e9a60, nargs=nargs@entry=1) at Python/clinic/import.c.h:488
#8  0x00005555556bd9ed in cfunction_vectorcall_FASTCALL (func=0x7ffff7c858b0, args=0x7ffff77e9a60, nargsf=<optimized out>, kwnames=<optimized out>) at Objects/methodobject.c:454
#9  0x000055555566a1bd in _PyVectorcall_Call (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, func=0x5555556bd990 <cfunction_vectorcall_FASTCALL>, callable=callable@entry=0x7ffff7c858b0, tuple=tuple@entry=0x7ffff77e9a40, kwargs=kwargs@entry=0x7ffff77dce90)
    at Objects/call.c:273
#10 0x000055555566a431 in _PyObject_Call (tstate=0x555555b97588 <_PyRuntime+330792>, callable=callable@entry=0x7ffff7c858b0, args=args@entry=0x7ffff77e9a40, kwargs=kwargs@entry=0x7ffff77dce90) at Objects/call.c:348
#11 0x000055555566a469 in PyObject_Call (callable=callable@entry=0x7ffff7c858b0, args=args@entry=0x7ffff77e9a40, kwargs=kwargs@entry=0x7ffff77dce90) at Objects/call.c:373
#12 0x00005555557a15a9 in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=0x7ffff7b5f500, throwflag=0) at Python/generated_cases.c.h:2461
#13 0x00005555557bbc02 in _PyEval_EvalFrame (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, frame=frame@entry=0x7ffff7b5f1e8, throwflag=throwflag@entry=0) at ./Include/internal/pycore_ceval.h:119
#14 0x00005555557bbdc7 in _PyEval_Vector (tstate=0x555555b97588 <_PyRuntime+330792>, func=0x7ffff7c89250, locals=locals@entry=0x0, args=0x7fffffffc8a0, argcount=<optimized out>, kwnames=0x0) at Python/ceval.c:1913
#15 0x0000555555668520 in _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:413
#16 0x000055555566886f in _PyObject_VectorcallTstate (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, callable=callable@entry=0x7ffff7c89250, args=args@entry=0x7fffffffc8a0, nargsf=nargsf@entry=2, kwnames=kwnames@entry=0x0)
    at ./Include/internal/pycore_call.h:169
#17 0x00005555556696d2 in object_vacall (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, base=base@entry=0x0, callable=0x7ffff7c89250, vargs=vargs@entry=0x7fffffffc920) at Objects/call.c:819
#18 0x000055555566980b in PyObject_CallMethodObjArgs (obj=0x0, name=<optimized out>) at Objects/call.c:880
#19 0x000055555580053a in import_find_and_load (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, abs_name=abs_name@entry=0x7ffff77b3b50) at Python/import.c:3692
#20 0x000055555580412a in PyImport_ImportModuleLevelObject (name=name@entry=0x7ffff77b3b50, globals=globals@entry=0x0, locals=locals@entry=0x0, fromlist=fromlist@entry=0x0, level=level@entry=0) at Python/import.c:3774
#21 0x0000555555793422 in builtin___import___impl (module=module@entry=0x7ffff7c64230, name=name@entry=0x7ffff77b3b50, globals=globals@entry=0x0, locals=locals@entry=0x0, fromlist=fromlist@entry=0x0, level=level@entry=0) at Python/bltinmodule.c:285
#22 0x0000555555793572 in builtin___import__ (module=0x7ffff7c64230, args=<optimized out>, args@entry=0x7ffff77b3b30, nargs=nargs@entry=1, kwnames=kwnames@entry=0x0) at Python/clinic/bltinmodule.c.h:110
#23 0x00005555556bd848 in cfunction_vectorcall_FASTCALL_KEYWORDS (func=0x7ffff7c64350, args=0x7ffff77b3b30, nargsf=<optimized out>, kwnames=0x0) at Objects/methodobject.c:470
#24 0x000055555566a1bd in _PyVectorcall_Call (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, func=0x5555556bd7f5 <cfunction_vectorcall_FASTCALL_KEYWORDS>, callable=callable@entry=0x7ffff7c64350, tuple=tuple@entry=0x7ffff77b3b10, 
    kwargs=kwargs@entry=0x7ffff77dc7d0) at Objects/call.c:273
#25 0x000055555566a431 in _PyObject_Call (tstate=0x555555b97588 <_PyRuntime+330792>, callable=callable@entry=0x7ffff7c64350, args=args@entry=0x7ffff77b3b10, kwargs=kwargs@entry=0x7ffff77dc7d0) at Objects/call.c:348
#26 0x000055555566a469 in PyObject_Call (callable=callable@entry=0x7ffff7c64350, args=args@entry=0x7ffff77b3b10, kwargs=kwargs@entry=0x7ffff77dc7d0) at Objects/call.c:373
#27 0x00005555557a15a9 in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=0x7ffff7b5f158, throwflag=0) at Python/generated_cases.c.h:2461
#28 0x00005555557bbc02 in _PyEval_EvalFrame (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, frame=frame@entry=0x7ffff7b5f080, throwflag=throwflag@entry=0) at ./Include/internal/pycore_ceval.h:119
#29 0x00005555557bbdc7 in _PyEval_Vector (tstate=0x555555b97588 <_PyRuntime+330792>, func=0x7ffff7c893d0, locals=locals@entry=0x0, args=0x7fffffffd080, argcount=<optimized out>, kwnames=0x0) at Python/ceval.c:1913
#30 0x0000555555668520 in _PyFunction_Vectorcall (func=<optimized out>, stack=<optimized out>, nargsf=<optimized out>, kwnames=<optimized out>) at Objects/call.c:413
#31 0x000055555566886f in _PyObject_VectorcallTstate (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, callable=callable@entry=0x7ffff7c893d0, args=args@entry=0x7fffffffd080, nargsf=nargsf@entry=3, kwnames=kwnames@entry=0x0)
    at ./Include/internal/pycore_call.h:169
#32 0x00005555556696d2 in object_vacall (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, base=base@entry=0x0, callable=0x7ffff7c893d0, vargs=vargs@entry=0x7fffffffd100) at Objects/call.c:819
#33 0x000055555566980b in PyObject_CallMethodObjArgs (obj=0x0, name=<optimized out>) at Objects/call.c:880
#34 0x0000555555804322 in PyImport_ImportModuleLevelObject (name=name@entry=0x7ffff77d7ec0, globals=<optimized out>, locals=locals@entry=0x7ffff77a7b30, fromlist=fromlist@entry=0x7ffff7c83fc0, level=level@entry=0) at Python/import.c:3842
#35 0x0000555555799f65 in _PyEval_ImportName (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, frame=frame@entry=0x7ffff7b5f020, name=name@entry=0x7ffff77d7ec0, fromlist=fromlist@entry=0x7ffff7c83fc0, level=level@entry=0x555555b4df18 <_PyRuntime+30136>)
    at Python/ceval.c:2838
#36 0x00005555557ab3aa in _PyEval_EvalFrameDefault (tstate=<optimized out>, frame=0x7ffff7b5f020, throwflag=0) at Python/generated_cases.c.h:6066
#37 0x00005555557bbc02 in _PyEval_EvalFrame (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, frame=frame@entry=0x7ffff7b5f020, throwflag=throwflag@entry=0) at ./Include/internal/pycore_ceval.h:119
#38 0x00005555557bbdc7 in _PyEval_Vector (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, func=func@entry=0x7ffff77e0650, locals=locals@entry=0x7ffff77a7b30, args=args@entry=0x0, argcount=argcount@entry=0, kwnames=kwnames@entry=0x0) at Python/ceval.c:1913
#39 0x00005555557bbebf in PyEval_EvalCode (co=co@entry=0x7ffff7791140, globals=globals@entry=0x7ffff77a7b30, locals=locals@entry=0x7ffff77a7b30) at Python/ceval.c:829
#40 0x0000555555831f4f in run_eval_code_obj (tstate=tstate@entry=0x555555b97588 <_PyRuntime+330792>, co=co@entry=0x7ffff7791140, globals=globals@entry=0x7ffff77a7b30, locals=locals@entry=0x7ffff77a7b30) at Python/pythonrun.c:1365
#41 0x00005555558320f5 in run_mod (mod=mod@entry=0x555555d2ccd0, filename=filename@entry=0x7ffff77b0770, globals=globals@entry=0x7ffff77a7b30, locals=locals@entry=0x7ffff77a7b30, flags=flags@entry=0x7fffffffd840, arena=arena@entry=0x7ffff77a7fa0, 
    interactive_src=0x7ffff77dc9a0, generate_new_source=0) at Python/pythonrun.c:1436
#42 0x0000555555832a3c in _PyRun_StringFlagsWithName (str=str@entry=0x7ffff77dca80 "from PyQt6 import QtCore\n", name=name@entry=0x7ffff77b0770, start=start@entry=257, globals=globals@entry=0x7ffff77a7b30, locals=locals@entry=0x7ffff77a7b30, 
    flags=flags@entry=0x7fffffffd840, generate_new_source=0) at Python/pythonrun.c:1259
#43 0x00005555558344fc in _PyRun_SimpleStringFlagsWithName (command=0x7ffff77dca80 "from PyQt6 import QtCore\n", name=name@entry=0x5555558d156c "<string>", flags=flags@entry=0x7fffffffd840) at Python/pythonrun.c:578
#44 0x000055555585c951 in pymain_run_command (command=<optimized out>) at Modules/main.c:255
#45 0x000055555585d6ec in pymain_run_python (exitcode=exitcode@entry=0x7fffffffd8e4) at Modules/main.c:671
#46 0x000055555585daf9 in Py_RunMain () at Modules/main.c:761
#47 0x000055555585db70 in pymain_main (args=args@entry=0x7fffffffd940) at Modules/main.c:791
#48 0x000055555585dc36 in Py_BytesMain (argc=<optimized out>, argv=<optimized out>) at Modules/main.c:815
#49 0x00005555555d8902 in main (argc=<optimized out>, argv=<optimized out>) at ./Programs/python.c:15

I was able to bisect this to 8614f86:

• gh-131525: Cache the result of tuple_hash #131529

cc @mdboom

I don't have a minimal reproducer unfortunately as I've never used the C API before; but according to the PyQt author:

Just by visual inspection of the code, I think the sequence of calls is...

static PyTypeObject BaseType {
     ...
};

PyType_Ready(&BaseType);
PyObject *base_tup = PyTuple_Pack(1, (PyObject *)&BaseType);
PyObject *base_ref = PyTuple_GET_ITEM(base_tup, 0);
Py_TYPE(base_ref);  // Crashes here (because base_ref is -1?)

...so I don't think I'm doing anything bad.

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.14.0a7 (tags/v3.14.0a7:29af6cee02f, Apr 12 2025, 21:45:20) [GCC 14.2.1 20250207]

[ZeroIntensity]

At a glance, there's probably some incorrect inheritance. #131529 added a hash field, and from the looks of it, that hash isn't being accounted for in the subtype structure, so the reference count is being treated as the hash (thus the -1 value). It would be nice to see the actual source here; where is PyQt6 hosted?

[The-Compiler]

The easiest way to get the canonical sources is from PyPI, I believe the interesting parts (sip_api_init_module and createClassType) are all in sip_core.c which is part of PyQt6-sip.

The same file also seems to be hosted here: https://github.com/Python-SIP/sip/blob/350f56b80fe8a4d027ad6b301be607cc8c921a19/sipbuild/module/source/13/10/sip_core.c#L5721

[neonene]

FYI, I could not confirm the crash on Windows, trying alpha7 with PyPI's PyQt5&6 binaries (PyTuple_GET_ITEM(bases, 0) did not show -1 in sip_core.c).

[The-Compiler]

The PyQt maintainer mentioned:

The sip module does not use the limited ABI and so must be built against the appropriate Python version.
[...]
The bug is what you would get if you were using the PyTuple_GET_ITEM macro from a pre-alpha7 header file against an alpha7 installation.

However, the pip install logs point at the correct headers:

gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_core.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_core.o

Full build log

$ .venv/bin/pip install --force-reinstall --verbose --no-cache --no-binary pyqt6-sip pyqt6-sip
Using pip 25.0.1 from /home/florian/proj/cpython/.venv/lib/python3.14/site-packages/pip (python 3.14)
Collecting pyqt6-sip
  Downloading pyqt6_sip-13.10.0.tar.gz (92 kB)
  Running command pip subprocess to install build dependencies
  Using pip 25.0.1 from /home/florian/proj/cpython/.venv/lib/python3.14/site-packages/pip (python 3.14)
  Collecting setuptools>=69.5
    Obtaining dependency information for setuptools>=69.5 from https://files.pythonhosted.org/packages/54/21/f43f0a1fa8b06b32812e0975981f4677d28e0f3271601dc88ac5a5b83220/setuptools-78.1.0-py3-none-any.whl.metadata
    Using cached setuptools-78.1.0-py3-none-any.whl.metadata (6.6 kB)
  Using cached setuptools-78.1.0-py3-none-any.whl (1.3 MB)
  Installing collected packages: setuptools
  Successfully installed setuptools-78.1.0
  Installing build dependencies ... done
  Running command Getting requirements to build wheel
  running egg_info
  writing PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to PyQt6_sip.egg-info/top_level.txt
  reading manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  Getting requirements to build wheel ... done
  Running command Preparing metadata (pyproject.toml)
  running dist_info
  creating /tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info
  writing /tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to /tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to /tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/top_level.txt
  writing manifest file '/tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest file '/tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file '/tmp/pip-modern-metadata-l8494dmc/PyQt6_sip.egg-info/SOURCES.txt'
  creating '/tmp/pip-modern-metadata-l8494dmc/pyqt6_sip-13.10.0.dist-info'
  Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: pyqt6-sip
  Running command Building wheel for pyqt6-sip (pyproject.toml)
  running bdist_wheel
  running build
  running build_ext
  building 'PyQt6.sip' extension
  creating build/temp.linux-x86_64-cpython-314-pydebug
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_array.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_array.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_core.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_core.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_descriptors.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_descriptors.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_enum.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_enum.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_int_convertors.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_int_convertors.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_object_map.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_object_map.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_threads.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_threads.o
  gcc -fsanitize=undefined -fsanitize=address -fno-omit-frame-pointer -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/proj/cpython/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_voidptr.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_voidptr.o
  creating build/lib.linux-x86_64-cpython-314-pydebug/PyQt6
  gcc -shared -fsanitize=undefined -fsanitize=address build/temp.linux-x86_64-cpython-314-pydebug/sip_array.o build/temp.linux-x86_64-cpython-314-pydebug/sip_core.o build/temp.linux-x86_64-cpython-314-pydebug/sip_descriptors.o build/temp.linux-x86_64-cpython-314-pydebug/sip_enum.o build/temp.linux-x86_64-cpython-314-pydebug/sip_int_convertors.o build/temp.linux-x86_64-cpython-314-pydebug/sip_object_map.o build/temp.linux-x86_64-cpython-314-pydebug/sip_threads.o build/temp.linux-x86_64-cpython-314-pydebug/sip_voidptr.o -o build/lib.linux-x86_64-cpython-314-pydebug/PyQt6/sip.cpython-314d-x86_64-linux-gnu.so
  installing to build/bdist.linux-x86_64/wheel
  running install
  running install_lib
  creating build/bdist.linux-x86_64/wheel
  creating build/bdist.linux-x86_64/wheel/PyQt6
  copying build/lib.linux-x86_64-cpython-314-pydebug/PyQt6/sip.cpython-314d-x86_64-linux-gnu.so -> build/bdist.linux-x86_64/wheel/./PyQt6
  running install_egg_info
  running egg_info
  writing PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to PyQt6_sip.egg-info/top_level.txt
  reading manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  Copying PyQt6_sip.egg-info to build/bdist.linux-x86_64/wheel/./PyQt6_sip-13.10.0-py3.14.egg-info
  running install_scripts
  creating build/bdist.linux-x86_64/wheel/pyqt6_sip-13.10.0.dist-info/WHEEL
  creating '/tmp/pip-wheel-6c083x41/.tmp-ibj91ot9/pyqt6_sip-13.10.0-cp314-cp314d-linux_x86_64.whl' and adding 'build/bdist.linux-x86_64/wheel' to it
  adding 'PyQt6/sip.cpython-314d-x86_64-linux-gnu.so'
  adding 'pyqt6_sip-13.10.0.dist-info/licenses/LICENSE'
  adding 'pyqt6_sip-13.10.0.dist-info/METADATA'
  adding 'pyqt6_sip-13.10.0.dist-info/WHEEL'
  adding 'pyqt6_sip-13.10.0.dist-info/top_level.txt'
  adding 'pyqt6_sip-13.10.0.dist-info/RECORD'
  removing build/bdist.linux-x86_64/wheel
  Building wheel for pyqt6-sip (pyproject.toml) ... done
  Created wheel for pyqt6-sip: filename=pyqt6_sip-13.10.0-cp314-cp314d-linux_x86_64.whl size=485291 sha256=fdc1488d5283a7b0b1d6b27b010d2d2741a045927b2fbf7b2067aa622e2ec09f
  Stored in directory: /tmp/pip-ephem-wheel-cache-gnvni3jb/wheels/a3/55/e6/a5e1824027bf660af13b0d226ab1e9b56803ba4f3331b25cca
Successfully built pyqt6-sip
Installing collected packages: pyqt6-sip
  Attempting uninstall: pyqt6-sip
    Found existing installation: PyQt6_sip 13.10.0
    Uninstalling PyQt6_sip-13.10.0:
      Removing file or directory /home/florian/proj/cpython/.venv/lib/python3.14/site-packages/PyQt6/sip.cpython-314d-x86_64-linux-gnu.so
      Removing file or directory /home/florian/proj/cpython/.venv/lib/python3.14/site-packages/pyqt6_sip-13.10.0.dist-info/
      Successfully uninstalled PyQt6_sip-13.10.0
Successfully installed pyqt6-sip-13.10.0

So I don't think that's the actual issue here?

[The-Compiler]

Huh. I just tried again, with a fresh CPython v3.14.0a7 build and a clean virtualenv and everything, and suddenly things look good now:

$ ~/proj/cpython/python -m venv .venv

$ .venv/bin/pip install --force-reinstall --verbose --no-cache --no-binary pyqt6-sip pyqt6-sip
Using pip 25.0.1 from /home/florian/tmp/132454/.venv/lib/python3.14/site-packages/pip (python 3.14)
Collecting pyqt6-sip
  Downloading pyqt6_sip-13.10.0.tar.gz (92 kB)
  Running command pip subprocess to install build dependencies
  Using pip 25.0.1 from /home/florian/tmp/132454/.venv/lib/python3.14/site-packages/pip (python 3.14)
  Collecting setuptools>=69.5
    Obtaining dependency information for setuptools>=69.5 from https://files.pythonhosted.org/packages/54/21/f43f0a1fa8b06b32812e0975981f4677d28e0f3271601dc88ac5a5b83220/setuptools-78.1.0-py3-none-any.whl.metadata
    Using cached setuptools-78.1.0-py3-none-any.whl.metadata (6.6 kB)
  Using cached setuptools-78.1.0-py3-none-any.whl (1.3 MB)
  Installing collected packages: setuptools
  Successfully installed setuptools-78.1.0
  Installing build dependencies ... done
  Running command Getting requirements to build wheel
  running egg_info
  writing PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to PyQt6_sip.egg-info/top_level.txt
  reading manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  Getting requirements to build wheel ... done
  Running command Preparing metadata (pyproject.toml)
  running dist_info
  creating /tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info
  writing /tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to /tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to /tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/top_level.txt
  writing manifest file '/tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest file '/tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file '/tmp/pip-modern-metadata-eh67bpja/PyQt6_sip.egg-info/SOURCES.txt'
  creating '/tmp/pip-modern-metadata-eh67bpja/pyqt6_sip-13.10.0.dist-info'
  Preparing metadata (pyproject.toml) ... done
Building wheels for collected packages: pyqt6-sip
  Running command Building wheel for pyqt6-sip (pyproject.toml)
  running bdist_wheel
  running build
  running build_ext
  building 'PyQt6.sip' extension
  creating build/temp.linux-x86_64-cpython-314-pydebug
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_array.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_array.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_core.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_core.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_descriptors.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_descriptors.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_enum.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_enum.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_int_convertors.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_int_convertors.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_object_map.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_object_map.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_threads.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_threads.o
  gcc -fno-strict-overflow -Wsign-compare -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -Og -Wall -fPIC -I/home/florian/tmp/132454/.venv/include -I/home/florian/proj/cpython/Include -I/home/florian/proj/cpython -c sip_voidptr.c -o build/temp.linux-x86_64-cpython-314-pydebug/sip_voidptr.o
  creating build/lib.linux-x86_64-cpython-314-pydebug/PyQt6
  gcc -shared build/temp.linux-x86_64-cpython-314-pydebug/sip_array.o build/temp.linux-x86_64-cpython-314-pydebug/sip_core.o build/temp.linux-x86_64-cpython-314-pydebug/sip_descriptors.o build/temp.linux-x86_64-cpython-314-pydebug/sip_enum.o build/temp.linux-x86_64-cpython-314-pydebug/sip_int_convertors.o build/temp.linux-x86_64-cpython-314-pydebug/sip_object_map.o build/temp.linux-x86_64-cpython-314-pydebug/sip_threads.o build/temp.linux-x86_64-cpython-314-pydebug/sip_voidptr.o -o build/lib.linux-x86_64-cpython-314-pydebug/PyQt6/sip.cpython-314d-x86_64-linux-gnu.so
  installing to build/bdist.linux-x86_64/wheel
  running install
  running install_lib
  creating build/bdist.linux-x86_64/wheel
  creating build/bdist.linux-x86_64/wheel/PyQt6
  copying build/lib.linux-x86_64-cpython-314-pydebug/PyQt6/sip.cpython-314d-x86_64-linux-gnu.so -> build/bdist.linux-x86_64/wheel/./PyQt6
  running install_egg_info
  running egg_info
  writing PyQt6_sip.egg-info/PKG-INFO
  writing dependency_links to PyQt6_sip.egg-info/dependency_links.txt
  writing top-level names to PyQt6_sip.egg-info/top_level.txt
  reading manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  reading manifest template 'MANIFEST.in'
  adding license file 'LICENSE'
  writing manifest file 'PyQt6_sip.egg-info/SOURCES.txt'
  Copying PyQt6_sip.egg-info to build/bdist.linux-x86_64/wheel/./PyQt6_sip-13.10.0-py3.14.egg-info
  running install_scripts
  creating build/bdist.linux-x86_64/wheel/pyqt6_sip-13.10.0.dist-info/WHEEL
  creating '/tmp/pip-wheel-l9d_y1gq/.tmp-cny6tsdb/pyqt6_sip-13.10.0-cp314-cp314d-linux_x86_64.whl' and adding 'build/bdist.linux-x86_64/wheel' to it
  adding 'PyQt6/sip.cpython-314d-x86_64-linux-gnu.so'
  adding 'pyqt6_sip-13.10.0.dist-info/licenses/LICENSE'
  adding 'pyqt6_sip-13.10.0.dist-info/METADATA'
  adding 'pyqt6_sip-13.10.0.dist-info/WHEEL'
  adding 'pyqt6_sip-13.10.0.dist-info/top_level.txt'
  adding 'pyqt6_sip-13.10.0.dist-info/RECORD'
  removing build/bdist.linux-x86_64/wheel
  Building wheel for pyqt6-sip (pyproject.toml) ... done
  Created wheel for pyqt6-sip: filename=pyqt6_sip-13.10.0-cp314-cp314d-linux_x86_64.whl size=227829 sha256=34e5b17dbbed4796c8ad78a9f81a4b0cb97bd67b573dd2c632d795d8e5e33e57
  Stored in directory: /tmp/pip-ephem-wheel-cache-8fzo12y4/wheels/a3/55/e6/a5e1824027bf660af13b0d226ab1e9b56803ba4f3331b25cca
Successfully built pyqt6-sip
Installing collected packages: pyqt6-sip
Successfully installed pyqt6-sip-13.10.0
.venv/bin/pip install --force-reinstall --verbose --no-cache --no-binary    4.70s user 0.34s system 95% cpu 5.295 total

$ .venv/bin/pip install PyQt6                                                                 
Collecting PyQt6
  Using cached PyQt6-6.9.0-cp39-abi3-manylinux_2_28_x86_64.whl.metadata (2.1 kB)
Requirement already satisfied: PyQt6-sip<14,>=13.8 in ./.venv/lib/python3.14/site-packages (from PyQt6) (13.10.0)
Collecting PyQt6-Qt6<6.10.0,>=6.9.0 (from PyQt6)
  Using cached PyQt6_Qt6-6.9.0-py3-none-manylinux_2_28_x86_64.whl.metadata (534 bytes)
Using cached PyQt6-6.9.0-cp39-abi3-manylinux_2_28_x86_64.whl (8.3 MB)
Using cached PyQt6_Qt6-6.9.0-py3-none-manylinux_2_28_x86_64.whl (81.8 MB)
Installing collected packages: PyQt6-Qt6, PyQt6
Successfully installed PyQt6-6.9.0 PyQt6-Qt6-6.9.0
.venv/bin/pip install PyQt6  2.05s user 0.25s system 92% cpu 2.474 total

$ .venv/bin/python -VV
Python 3.14.0a7 (tags/v3.14.0a7:29af6cee02f, Apr 13 2025, 13:04:42) [GCC 14.2.1 20250207]

$ .venv/bin/python -c "from PyQt6 import QtCore"

Not sure what to make of this. So maybe there isn't any issue after all?

[ZeroIntensity]

Is it possible you used a version built for a prior 3.14 alpha? The ABI changes between alphas, so that would make sense.

[The-Compiler]

Not deliberately! I tried a clean build before and could still reproduce the issue, but there must have been some caching going on somewhere.

Originally I noticed the issue on GitHub Actions, and there it was because I'm caching ~/.cache/pip but didn't have the Python alpha as part of the cache key (and neither did pip, apparently?). After nuking the cache there as well, everything seems to work on CI again, so this probably was it.

Sorry for the noise!