I was under the impression that between calls to beginResetModel() and endResetModel() for a subclass of QAbstractItemModel I could change the model data in whatever way I wanted. However, the behavior described below suggests that either I don't understand how to actually reset a QAbstractItemModel, or there is a bug in PySide6 and PyQt6. Probably the former, so hopefully someone will set me straight.

1. I began with the editable tree model example from https://doc.qt.io/qtforpython-6/examples/example_widgets_itemviews_editabletreemodel.html. All of those files are here with a few edits as described below.
2. I added the function reset_from_data() to TreeModel in treemodel.py. This function calls beginResetModel(), then executes the same model initialization code as in the original {}init function, then calls endResetModel().
3. I added a menu action in mainwindow.py for resetting the model and a slot reset_model() which calls the model's reset_from_data() function.
4. To test this function, run main.py to bring up the tree model view, then select Reset Model from the Actions menu. If you want you can add some new rows first (use the Actions menu) so you can be sure that the model was indeed reset.
5. After the model is reset, clicking on the view often causes the app to crash!

Steps to reproduce behavior:

1. conda create -n test python
2. conda activate test
3. pip install PySide6 <-- Note that I found this same behavior occurs with PyQt6 as well.
4. Downoad the GitHub repo at https://github.com/marcel-goldschen-ohm/PyQt-QAbstractItemModel-ResetModel-Bug/ which has all of the files with my edits (same as the files attached here).
5. Go to the downloaded repo folder and run python main.py
6. This will launch an editable tree view widget which should work as expected.
7. Next select Reset Model from the Actions menu which will call the model's reset_from_data() function that I added (see above).
8. This visually resets the model as expected!
9. However, now clicking on the tree view often causes the app to crash, which otherwise does NOT happen if the model was not reset.

Here is an example of the error log when the app crashes:

 {{2023-07-05 17:38:50.335 python[13570:224418] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndexedSubscript:]: index 10 beyond bounds for empty array'

• • • First throw call stack:
      (
      0 CoreFoundation 0x000000019ded43e8 __exceptionPreprocess + 176
      1 libobjc.A.dylib 0x000000019da1eea8 objc_exception_throw + 60
      2 CoreFoundation 0x000000019dfb9c94 -[__NSCFString characterAtIndex:].cold.1 + 0
      3 CoreFoundation 0x000000019de45f98 -[__NSArrayM objectAtIndexedSubscript:] + 188
      4 libqcocoa.dylib 0x000000011e174124 _ZN20QCocoaSystemTrayIcon13emitActivatedEv + 269336
      5 libqcocoa.dylib 0x000000011e1741a8 _ZN20QCocoaSystemTrayIcon13emitActivatedEv + 269468
      6 libqcocoa.dylib 0x000000011e17277c _ZN20QCocoaSystemTrayIcon13emitActivatedEv + 262768
      7 QtWidgets 0x000000011c5810b0 ZN9QTreeView14currentChangedERK11QModelIndexS2 + 452
      8 QtCore 0x000000011e299788 _ZN11QMetaObject8activateEP7QObjectPKS_iPPv + 3780
      9 QtCore 0x000000011e45e18c _ZN19QItemSelectionModel15setCurrentIndexERK11QModelIndex6QFlagsINS_13SelectionFlagEE + 324
      10 QtWidgets 0x000000011c50a31c _ZN17QAbstractItemView15mousePressEventEP11QMouseEvent + 880
      11 QtWidgets 0x000000011c579f7c _ZN9QTreeView15mousePressEventEP11QMouseEvent + 260
      12 QtWidgets 0x000000011c2de330 _ZN7QWidget5eventEP6QEvent + 132
      13 QtWidgets 0x000000011c362060 _ZN6QFrame5eventEP6QEvent + 56
      14 QtWidgets 0x000000011c509f3c _ZN17QAbstractItemView13viewportEventEP6QEvent + 988
      15 QtWidgets 0x000000011c57737c _ZN9QTreeView13viewportEventEP6QEvent + 328
      16 QtCore 0x000000011e25025c _ZN23QCoreApplicationPrivate29sendThroughObjectEventFiltersEP7QObjectP6QEvent + 244
      17 QtWidgets 0x000000011c294fcc _ZN19QApplicationPrivate13notify_helperEP7QObjectP6QEvent + 240
      18 QtWidgets 0x000000011c29703c _ZN12QApplication6notifyEP7QObjectP6QEvent + 5100
      19 QtCore 0x000000011e24ff88 _ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent + 292
      20 QtWidgets 0x000000011c29558c _ZN19QApplicationPrivate14sendMouseEventEP7QWidgetP11QMouseEventS1_S1_PS1_R8QPointerIS0_Ebb + 808
      21 QtWidgets 0x000000011c2f29b0 _ZNK21QWidgetRepaintManager3rhiEv + 9912
      22 QtWidgets 0x000000011c2f1c68 _ZNK21QWidgetRepaintManager3rhiEv + 6512
      23 QtWidgets 0x000000011c294fec _ZN19QApplicationPrivate13notify_helperEP7QObjectP6QEvent + 272
      24 QtWidgets 0x000000011c295e50 _ZN12QApplication6notifyEP7QObjectP6QEvent + 512
      25 QtCore 0x000000011e24ff88 _ZN16QCoreApplication15notifyInternal2EP7QObjectP6QEvent + 292
      26 QtGui 0x000000011b746794 _ZN22QGuiApplicationPrivate17processMouseEventEPN29QWindowSystemInterfacePrivate10MouseEventE + 1748
      27 QtGui 0x000000011b79daa4 _ZN22QWindowSystemInterface22sendWindowSystemEventsE6QFlagsIN10QEventLoop17ProcessEventsFlagEE + 396
      28 libqcocoa.dylib 0x000000011e117d40 qt_plugin_instance + 54740
      29 CoreFoundation 0x000000019de59a08 {}CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION{} + 28
      30 CoreFoundation 0x000000019de5999c __CFRunLoopDoSource0 + 176
      31 CoreFoundation 0x000000019de5970c __CFRunLoopDoSources0 + 244
      32 CoreFoundation 0x000000019de58310 __CFRunLoopRun + 836
      33 CoreFoundation 0x000000019de57878 CFRunLoopRunSpecific + 612
      34 HIToolbox 0x00000001a7537fa0 RunCurrentEventLoopInMode + 292
      35 HIToolbox 0x00000001a7537c30 ReceiveNextEventCommon + 236
      36 HIToolbox 0x00000001a7537b2c _BlockUntilNextEventMatchingListInModeWithFilter + 72
      37 AppKit 0x00000001a10dd84c _DPSNextEvent + 632
      38 AppKit 0x00000001a10dc9dc -[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:] + 728
      39 AppKit 0x00000001a10d0e0c -[NSApplication run] + 464
      40 libqcocoa.dylib 0x000000011e116644 qt_plugin_instance + 48856
      41 QtCore 0x000000011e2598fc _ZN10QEventLoop4execE6QFlagsINS_17ProcessEventsFlagEE + 532
      42 QtCore 0x000000011e250614 _ZN16QCoreApplication4execEv + 112
      43 QtWidgets.abi3.so 0x000000011d1771a4 _ZL25Sbk_QApplicationFunc_execP7_object + 52
      44 python3.11 0x0000000102873e48 cfunction_vectorcall_NOARGS + 296
      45 python3.11 0x000000010281cb04 PyObject_Vectorcall + 76
      46 python3.11 0x000000010291ca58 _PyEval_EvalFrameDefault + 47160
      47 python3.11 0x000000010291029c PyEval_EvalCode + 220
      48 python3.11 0x000000010297601c run_mod + 144
      49 python3.11 0x0000000102975a7c _PyRun_SimpleFileObject + 1264
      50 python3.11 0x0000000102974b38 _PyRun_AnyFileObject + 240
      51 python3.11 0x000000010299b304 Py_RunMain + 3128
      52 python3.11 0x000000010299c198 pymain_main + 1312
      53 python3.11 0x00000001027c0074 main + 56
      54 dyld 0x000000019da4fe50 start + 2544
      )
      libc++abi: terminating with uncaught exception of type NSException}}
       

Either this is a bug in PySide6 and PyQt6, or I don't understand how to use beginResetModel() ... endResetModel().

Any ideas?

OS specific?

Note that I am on a Mac with an M1 Max processor. This may be relevant?