[Python 3.12] SystemError and other undesirable behavior

[jaraco]

Consider the following test:

import pytest


class SpecialException(Exception):
    pass


class Base:
    def __getattr__(self, name):
        raise AttributeError(name)


class Propertious(Base):
    @property
    def foo_special(self):
        raise SpecialException


def test_attr():
    p = Propertious()
    with pytest.raises(SpecialException):
        p.foo_special

The test passes on Python 3.11, but on Python 3.12.0a7, fails thus:

 $ py -3.12 -m pip-run pytest -- -m pytest attr.py
============================================================= test session starts ==============================================================
platform darwin -- Python 3.12.0a7, pytest-7.3.1, pluggy-1.0.0
rootdir: /Users/jaraco/draft
plugins: anyio-3.6.2
collected 1 item                                                                                                                               

attr.py F                                                                                                                                [100%]

=================================================================== FAILURES ===================================================================
__________________________________________________________________ test_attr ___________________________________________________________________

self = <attr.Propertious object at 0x101aa9580>

    @property
    def foo_special(self):
>       raise SpecialException
E       attr.SpecialException

attr.py:16: SpecialException

The above exception was the direct cause of the following exception:

    def test_attr():
        p = Propertious()
        with pytest.raises(SpecialException):
>           p.foo_special

attr.py:22: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <attr.Propertious object at 0x101aa9580>, name = 'foo_special'

    def __getattr__(self, name):
>       raise AttributeError(name)
E       SystemError: <class 'AttributeError'> returned a result with an exception set

attr.py:10: SystemError
=========================================================== short test summary info ============================================================
FAILED attr.py::test_attr - SystemError: <class 'AttributeError'> returned a result with an exception set
============================================================== 1 failed in 0.02s ===============================================================

I discovered the issue when troubleshooting a strange failure of jaraco.abode on Python 3.12. In that real-world example, tests fail when tests check for an expected exception during set_status, during which _control_url is accessed, but instead of being handled solely by the property on the class, somehow the superclass' getattr is evoked:

  stream = open(filename)
tests/mock/devices/secure_barrier.py ..
/home/runner/work/jaraco.abode/jaraco.abode/.tox/python/lib/python3.12/site-packages/blib2to3/pgen2/pgen.py:42: EncodingWarning: 'encoding' argument not specified
  stream = open(filename)
tests/mock/devices/siren.py ..
/home/runner/work/jaraco.abode/jaraco.abode/.tox/python/lib/python3.12/site-packages/blib2to3/pgen2/pgen.py:42: EncodingWarning: 'encoding' argument not specified
  stream = open(filename)
tests/mock/devices/status_display.py ..
/home/runner/work/jaraco.abode/jaraco.abode/.tox/python/lib/python3.12/site-packages/blib2to3/pgen2/pgen.py:42: EncodingWarning: 'encoding' argument not specified
  stream = open(filename)
tests/mock/devices/unknown.py ..
/home/runner/work/jaraco.abode/jaraco.abode/.tox/python/lib/python3.12/site-packages/blib2to3/pgen2/pgen.py:42: EncodingWarning: 'encoding' argument not specified
  stream = open(filename)
tests/mock/devices/valve.py ..
/home/runner/work/jaraco.abode/jaraco.abode/.tox/python/lib/python3.12/site-packages/blib2to3/pgen2/pgen.py:42: EncodingWarning: 'encoding' argument not specified
  stream = open(filename)
tests/mock/devices/water_sensor.py ..

=================================== FAILURES ===================================
________________________ TestDevice.test_no_control_url ________________________

self = <jaraco.abode.devices.binary_sensor.Connectivity object at 0x7f4f1a304950>
name = '_control_url'

    def __getattr__(self, name):
        try:
>           return self._state[name]
E           KeyError: '_control_url'

jaraco/abode/state.py:19: KeyError

The above exception was the direct cause of the following exception:

self = <tests.test_device.TestDevice object at 0x7f4f218a35c0>
m = <requests_mock.mocker.Mocker object at 0x7f4f1b7d3a40>

    def test_no_control_url(self, m):
        """Check that devices return false without control url's."""
        # Set up URLs
        m.post(urls.LOGIN, json=LOGIN.post_response_ok())
        m.get(urls.OAUTH_TOKEN, json=OAUTH_CLAIMS.get_response_ok())
        m.post(urls.LOGOUT, json=LOGOUT.post_response_ok())
        m.get(urls.PANEL, json=PANEL.get_response_ok())
    
        m.get(urls.DEVICES, json=GLASS.device(status=STATUS.ONLINE))
    
        # Logout to reset everything
        self.client.logout()
    
        # Get device
        device = self.client.get_device(GLASS.DEVICE_ID)
    
        assert device is not None
        with pytest.raises(jaraco.abode.Exception):
>           device.set_status(1)

tests/test_device.py:254: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
jaraco/abode/devices/base.py:34: in set_status
    path=self._control_url,
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <jaraco.abode.devices.binary_sensor.Connectivity object at 0x7f4f1a304950>
name = '_control_url'

    def __getattr__(self, name):
        try:
            return self._state[name]
        except KeyError as exc:
>           raise AttributeError(name) from exc
E           AttributeError: _control_url

jaraco/abode/state.py:21: AttributeError

The failure mode in the repro isn't precisely the same, but it's close, and I suspect it will trace to the same cause.

[RonnyPfannschmidt]

It's a know cpython bug, is fixed upstream but not yet released

[jaraco]

Glad to hear. I tried to find the CPython bug, but couldn't. If anyone knows which bug it was, I'd be interested in reading up on it. In the meantime, I'll watch for alpha 8 or beta 1 to fix it.

[RonnyPfannschmidt]

python/cpython#103551

noted via #10894 (comment) (which is why i didn't find it in the pytest issues )