RuntimeError: wrapped C/C++ object of type QLabel has been deleted

[multimeric]

I've been hitting the above error. It seems to happen when we destroy and then create a viewer in quick succession. One such case where this happens is when running pytest.

Here is a minimal example. You will have to run pytest test.py for this to work.

from magicclass import magicclass
from magicgui import magicgui, widgets

@magicclass
class X:
    main_heading = widgets.Label(value="foo")

def test_a(make_napari_viewer):
    viewer = make_napari_viewer()
    widget = X()
    viewer.window.add_dock_widget(widget)

def test_b(make_napari_viewer):
    viewer = make_napari_viewer()
    widget = X()
    viewer.window.add_dock_widget(widget)

Full traceback:

Traceback (most recent call last):
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/runner.py", line 341, in from_call
    result: Optional[TResult] = func()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/runner.py", line 262, in <lambda>
    lambda: ihook(item=item, **kwds), when=when, reraise=reraise
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_hooks.py", line 433, in __call__
    return self._hookexec(self.name, self._hookimpls, kwargs, firstresult)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_manager.py", line 112, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_callers.py", line 155, in _multicall
    return outcome.get_result()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_result.py", line 108, in get_result
    raise exc.with_traceback(exc.__traceback__)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_callers.py", line 80, in _multicall
    res = hook_impl.function(*args)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/runner.py", line 177, in pytest_runtest_call
    raise e
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/runner.py", line 169, in pytest_runtest_call
    item.runtest()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/python.py", line 1788, in runtest
    self.ihook.pytest_pyfunc_call(pyfuncitem=self)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_hooks.py", line 433, in __call__
    return self._hookexec(self.name, self._hookimpls, kwargs, firstresult)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_manager.py", line 112, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_callers.py", line 116, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/pluggy/_callers.py", line 80, in _multicall
    res = hook_impl.function(*args)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/_pytest/python.py", line 194, in pytest_pyfunc_call
    result = testfunction(**testargs)
  File "/Users/milton.m/Programming/napari_lattice/plugin/tests/test_dock_widget.py", line 36, in test_plugin_initialize
    ui = _napari_lattice_widget_wrapper()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/napari_lattice/_dock_widget.py", line 1155, in _napari_lattice_widget_wrapper
    widget = LLSZWidget()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/core.py", line 204, in __init__
    self._convert_attributes_into_widgets()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/class_gui.py", line 289, in _convert_attributes_into_widgets
    format_error(e, _hist, name, attr)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/utils.py", line 84, in format_error
    raise e
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/class_gui.py", line 142, in _convert_attributes_into_widgets
    widget = attr()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/core.py", line 204, in __init__
    self._convert_attributes_into_widgets()
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/class_gui.py", line 289, in _convert_attributes_into_widgets
    format_error(e, _hist, name, attr)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/utils.py", line 90, in format_error
    raise construction_err from None
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/class_gui.py", line 283, in _convert_attributes_into_widgets
    self._fast_insert(n_insert, widget)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/_gui/class_gui.py", line 341, in _fast_insert
    self._widget._mgui_insert_widget(key, _widget)
  File "/opt/anaconda3/envs/napari-env/lib/python3.9/site-packages/magicclass/widgets/containers.py", line 70, in _mgui_insert_widget
    self._splitter.insertWidget(position, widget.native)
magicclass._gui.utils.MagicClassConstructionError: 

                LlszMenu (<class 'magicclass._gui._base._MagicTemplateMeta'>) <--- Error


                main_heading (<class 'magicgui.widgets.Label'>) <--- Error

RuntimeError: wrapped C/C++ object of type QLabel has been deleted

I believe this is another result of the issue discussed here: napari/napari#4377. If I construct the class inside a factory function as follows, the problem goes away, but this is obviously not desirable:

from magicclass import magicclass
from magicgui import magicgui, widgets

def make_x():
    @magicclass
    class X:
        main_heading = widgets.Label(value="foo")
    return X

def test_a(make_napari_viewer):
    viewer = make_napari_viewer()
    widget = make_x()()
    viewer.window.add_dock_widget(widget)

def test_b(make_napari_viewer):
    viewer = make_napari_viewer()
    widget = make_x()()
    viewer.window.add_dock_widget(widget)

[hanjinliu]

Could you try using field?

from magicclass import magicclass, field

@magicclass
class X:
    main_heading = field("foo", widget_type="Label")

It seems like the QLabel widget is destroyed at the end of the first test to me.

[multimeric]

Great, this seems to fix it. Thanks for the quick response!