Fix PySide6 compatibility issues causing segfaults in test suite

- Use `object` instead of C++ type strings in Signal declarations
  (PySide6 segfaults with "QMouseEvent", "QEvent", "QPointF" strings)
- Check QObject validity via `is_qobject_valid()` before accessing
  widgets in __del__, closeEvent, and panel close operations
- Restructure BaseSyncPlot.__init__ to defer widget operations until
  after Qt __init__ completes (PySide6 requirement)
- Replace deprecated `exec_()` calls with `exec()`

Author: PierreRaybaut

plotpy/events.py

@@ -727,7 +727,7 @@ class ClickHandler(QC.QObject):
     """
 
     #: Signal emitted by ClickHandler on mouse click
-    SIG_CLICK_EVENT = QC.Signal(object, "QEvent")
+    SIG_CLICK_EVENT = QC.Signal(object, object)
 
     def __init__(
         self,
@@ -1134,16 +1134,16 @@ class QtDragHandler(DragHandler):
     """Class to handle drag events using Qt signals."""
 
     #: Signal emitted by QtDragHandler when starting tracking
-    SIG_START_TRACKING = QC.Signal(object, "QMouseEvent")
+    SIG_START_TRACKING = QC.Signal(object, object)
 
     #: Signal emitted by QtDragHandler when stopping tracking and not moving
-    SIG_STOP_NOT_MOVING = QC.Signal(object, "QMouseEvent")
+    SIG_STOP_NOT_MOVING = QC.Signal(object, object)
 
     #: Signal emitted by QtDragHandler when stopping tracking and moving
-    SIG_STOP_MOVING = QC.Signal(object, "QMouseEvent")
+    SIG_STOP_MOVING = QC.Signal(object, object)
 
     #: Signal emitted by QtDragHandler when moving
-    SIG_MOVE = QC.Signal(object, "QMouseEvent")
+    SIG_MOVE = QC.Signal(object, object)
 
     def start_tracking(self, filter: StatefulEventFilter, event: QMouseEvent) -> None:
         """Starts tracking the drag event.
@@ -1636,7 +1636,7 @@ class RectangularSelectionHandler(DragHandler):
     """
 
     #: Signal emitted by RectangularSelectionHandler when ending selection
-    SIG_END_RECT = QC.Signal(object, "QPointF", "QPointF")
+    SIG_END_RECT = QC.Signal(object, object, object)
 
     def __init__(
         self,

plotpy/plot/base.py

@@ -27,6 +27,7 @@
 import numpy as np
 import qwt
 from guidata.configtools import get_font
+from guidata.qthelpers import is_qobject_valid
 from qtpy import QtCore as QC
 from qtpy import QtGui as QG
 from qtpy import QtWidgets as QW
@@ -447,18 +448,16 @@ def __del__(self):
         # Sometimes, an obscure exception happens when we quit an application
         # because if we don't remove the eventFilter it can still be called
         # after the filter object has been destroyed by Python.
+        # Note: PySide6 segfaults instead of raising RuntimeError when accessing
+        # a deleted C++ object, so we must check validity before calling methods.
+        if not is_qobject_valid(self):
+            return
         canvas: qwt.QwtPlotCanvas = self.canvas()
-        if canvas:
+        if canvas and is_qobject_valid(canvas) and is_qobject_valid(self.filter):
             try:
                 canvas.removeEventFilter(self.filter)
-            except RuntimeError as exc:
-                # Depending on which widget owns the plot,
-                # Qt may have already deleted the canvas when
-                # the plot is deleted.
-                if "C++ object" not in str(exc):
-                    raise
-            except ValueError:
-                # This happens when object has already been deleted
+            except (RuntimeError, ValueError):
+                # Widget/filter may have already been deleted
                 pass
 
     def update_color_mode(self) -> None:

plotpy/plot/interactive.py

@@ -19,7 +19,7 @@
 import numpy as np
 from guidata.configtools import get_icon
 from guidata.env import execenv
-from guidata.qthelpers import win32_fix_title_bar_background
+from guidata.qthelpers import is_qobject_valid, win32_fix_title_bar_background
 from qtpy import QtCore as QC
 from qtpy import QtGui as QG
 from qtpy import QtWidgets as QW
@@ -94,10 +94,9 @@ def closeEvent(self, event):
         if _figures.pop(figure_title) == _current_fig:
             _current_fig = None
             _current_axes = None
-        self.itemlist.close()
-        self.contrast.close()
-        self.xcsw.close()
-        self.ycsw.close()
+        for panel in (self.itemlist, self.contrast, self.xcsw, self.ycsw):
+            if is_qobject_valid(panel):
+                panel.close()
         event.accept()
 
     def add_plot(self, i, j, plot):

plotpy/plot/plotwidget.py

@@ -8,7 +8,7 @@
 from typing import TYPE_CHECKING, Any
 
 from guidata.configtools import get_icon
-from guidata.qthelpers import win32_fix_title_bar_background
+from guidata.qthelpers import is_qobject_valid, win32_fix_title_bar_background
 from qtpy import QtCore as QC
 from qtpy import QtGui as QG
 from qtpy import QtWidgets as QW
@@ -827,7 +827,9 @@ def closeEvent(self, event) -> None:
         # parent widget: otherwise, this panel will stay open after the main
         # window has been closed which is not the expected behavior)
         for panel in self.manager.panels:
-            self.manager.get_panel(panel).close()
+            panel_widget = self.manager.get_panel(panel)
+            if is_qobject_valid(panel_widget):
+                panel_widget.close()
         QW.QMainWindow.closeEvent(self, event)
 
 
@@ -903,16 +905,30 @@ def __init__(
     ) -> None:
         self.manager = PlotManager(None)
         self.manager.set_main(self)
-        self.subplotwidget = SubplotWidget(self.manager, parent=self, options=options)
+        # Note: parent is not set here and widget operations on `self` are
+        # deferred to _finalize_init() because PySide6 requires the subclass's
+        # __init__ to have fully completed before widget methods can be called.
+        self.subplotwidget = SubplotWidget(self.manager, parent=None, options=options)
+        self._toolbar_visible = toolbar
+        self.auto_tools = auto_tools
+        self._rescale_timer: QC.QTimer | None = None
+        self._init_title = title
+        self._init_icon = icon
+        self._init_size = size
+
+    def _finalize_init(self) -> None:
+        """Finalize initialization after Qt widget __init__ has completed.
+
+        This is called by subclasses in their __init__ after calling both
+        QMainWindow/QDialog.__init__ and BaseSyncPlot.__init__.
+        """
         self.toolbar = QW.QToolBar(_("Tools"), self)
-        self.toolbar.setVisible(toolbar)
+        self.toolbar.setVisible(self._toolbar_visible)
         self.manager.add_toolbar(self.toolbar, "default")
         self.toolbar.setMovable(True)
         self.toolbar.setFloatable(True)
-        self.auto_tools = auto_tools
-        self._rescale_timer: QC.QTimer | None = None
-        set_widget_title_icon(self, title, icon, size)
-        # Note: setup_layout() is called by subclasses after Qt widget initialization
+        set_widget_title_icon(self, self._init_title, self._init_icon, self._init_size)
+        # Note: setup_layout() is called by subclasses after _finalize_init()
 
     def setup_layout(self) -> None:
         """Setup the layout - to be implemented by subclasses"""
@@ -1048,8 +1064,9 @@ def __init__(
     ) -> None:
         self.subplotwidget: SubplotWidget
         self.toolbar: QW.QToolBar
-        QW.QMainWindow.__init__(self, parent)
         BaseSyncPlot.__init__(self, toolbar, options, auto_tools, title, icon, size)
+        QW.QMainWindow.__init__(self, parent)
+        self._finalize_init()
         self.setup_layout()
 
     def showEvent(self, event):  # pylint: disable=C0103
@@ -1107,8 +1124,9 @@ def __init__(
     ) -> None:
         self.subplotwidget: SubplotWidget
         self.toolbar: QW.QToolBar
-        QW.QDialog.__init__(self, parent)
         BaseSyncPlot.__init__(self, toolbar, options, auto_tools, title, icon, size)
+        QW.QDialog.__init__(self, parent)
+        self._finalize_init()
         self.setup_layout()
         self.setWindowFlags(QC.Qt.Window)
 

plotpy/tests/widgets/test_plot_timecurve.py

@@ -416,4 +416,4 @@ def update_all_curves(self, force=True):
     #    win.showMaximized()
     win.resize(800, 400)
     win.show()
-    app.exec_()
+    app.exec()

plotpy/tools/curve.py

@@ -1266,7 +1266,7 @@ def edit_curve_data(item: CurveItem) -> None:
 
     dialog = ArrayEditor(item.plot())
     dialog.setup_and_check(data)
-    if dialog.exec_():
+    if dialog.exec():
         if data.shape[1] > 2:
             if data.shape[1] == 3:
                 x, y, tmp = data.T

plotpy/tools/image.py

@@ -1372,4 +1372,4 @@ def edit_image_data(item) -> None:
     """Edit image item data in array editor"""
     dialog = ArrayEditor(item.plot())
     dialog.setup_and_check(item.data)
-    dialog.exec_()
+    dialog.exec()