Python 3.14.0a4: TypeError: <class '…'> has no usable non-default attributes

[musicinmybrain]

In Fedora, we’re already testing Python packages with pre-releases of Python 3.14, which will be included in Fedora 43 in late 2025. This report is based on a downstream issue that was filed as part of that testing.

It seems like the regressions in the test suite are all associated with a single type of error, of the form TypeError: <class '…'> has no usable non-default attributes.

A “control” test, showing that everything is fine on Python 3.13:

$ uv venv _e
Using CPython 3.13.1 interpreter at: /usr/bin/python3
Creating virtual environment at: _e
Activate with: source _e/bin/activate
$ . _e/bin/activate
(_e) $ uv pip install tox pdm
[…]
(_e) $ tox -e py313
[…]
============================ 827 passed, 6 skipped, 15 xfailed in 23.58s =============================

Now, after commenting out the orjson extra since we won’t be able to uv pip install it successfully on Python 3.14 yet:

(_e) $ tox -e py314

Ignoring the failures and errors (No module named 'orjson') due to the now-missing orjson dependency:

====================================== short test summary info =======================================
FAILED tests/strategies/test_include_subclasses.py::test_structure_as_union - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
FAILED tests/strategies/test_include_subclasses.py::test_overrides[wo-union-strategy-grandchild-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
FAILED tests/strategies/test_include_subclasses.py::test_structuring_unstructuring_unknown_subclass - TypeError: <class 'tests.strategies.test_include_subclasses.test_structuring_unstructuring_unknow...
FAILED tests/strategies/test_include_subclasses.py::test_overrides[wo-union-strategy-parent-only] - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
FAILED tests/strategies/test_include_subclasses.py::test_overrides[wo-union-strategy-child1-only] - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
FAILED tests/strategies/test_include_subclasses.py::test_overrides[wo-union-strategy-child2-only] - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-parent-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-union-compose-grandchild] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-non-union-compose-child] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-child1-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-child1-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-non-union-compose-parent] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-non-union-compose-grandchild] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-child2-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_circular_reference[with-subclasses] - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-child2-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-union-container] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-non-union-compose-child] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-grandchild-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-grandchild-only] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-non-union-container] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-non-union-compose-grandchild] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-union-compose-parent] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-parent-only] - TypeError: <class 'tests.strategies.test_include_subclasses.GrandChild'> has no usable non-defaul...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-union-compose-parent] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-union-container] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-union-compose-child] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-union-compose-child] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_structuring_with_inheritance[with-subclasses-non-union-container] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-union-compose-grandchild] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...
ERROR tests/strategies/test_include_subclasses.py::test_unstructuring_with_inheritance[with-subclasses-non-union-compose-parent] - TypeError: <class 'tests.strategies.test_include_subclasses.Child1'> has no usable non-default at...

[hroncok]

Could it perhaps be related to https://docs.python.org/3.14/whatsnew/3.14.html#whatsnew314-pep649 similarly to jcrist/msgspec#810 ?