Deleting a parent layout in on_change function (SIGSEGV Error)

Question

I have a QComboBox, cbo_box, nested in a frame, self.ui.frameFilterControls, with: cbo_box.currentTextChanged.connect(self.choice_changed). In self.choice_changed(), I call a function which clears the frames layout, including cbo_box, and then regenerates the layout with appropriate controls (including a new cbo_box):

layout = self.ui.frameFilterControls.layout()
if layout is not None:
    #clear layout
    for i in reversed(range(layout.count())):
        layout.itemAt(i).widget().setParent(None)

The problem I am having is that when self.choice_changed() returns, it throws a SIGSEGV error:

Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

I am guessing because it has no-where to return to, but I am not sure. I am wondering if it is possible to instead of calling the function that deletes and recreates the controls in the on_change of cbo_box if I could schedule it to be evaluated at the next form update, or something along those lines?

---

EDIT:

I have produced a minimal example which reproduces the behavior.

from PySide6 import QtCore, QtWidgets
from PySide6.QtWidgets import (QApplication, QListWidgetItem, QGridLayout, QVBoxLayout, QLineEdit, QComboBox)
import sys

#from output of designer -> simple main form with a frame for a starting point
class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(381, 357)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.frame = QtWidgets.QFrame(self.centralwidget)
        self.frame.setFrameShape(QtWidgets.QFrame.StyledPanel)
        self.frame.setFrameShadow(QtWidgets.QFrame.Raised)
        self.frame.setObjectName("frame")
        self.verticalLayout_2 = QtWidgets.QVBoxLayout(self.frame)
        self.verticalLayout_2.setObjectName("verticalLayout_2")
        self.pushButton = QtWidgets.QPushButton(self.frame)
        self.pushButton.setObjectName("pushButton")
        self.verticalLayout_2.addWidget(self.pushButton)
        self.verticalLayout.addWidget(self.frame)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 381, 22))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))


class MainGUI(QtWidgets.QMainWindow):
    def __init__(self, parent=None):
        super(MainGUI, self).__init__(parent)
        self.ui = Ui_MainWindow()
        self.ui.setupUi(self)
        self.set_frame_controls()

    def set_frame_controls(self):
        layout = self.ui.frame.layout()
        if layout is not None:
            #clear layout
            for i in reversed(range(layout.count())):
                layout.itemAt(i).widget().setParent(None)

        cbo_box = QComboBox()
        cbo_box.addItem("test 1")
        cbo_box.addItem("test 2")
        cbo_box.currentTextChanged.connect(self.choice_changed)
        layout.addWidget(cbo_box)

    def choice_changed(self):
        print("choice_changed")
        cbo_box = self.sender()
        self.set_frame_controls()
        print("end choice changed")

def main():
    app = QApplication(sys.argv)
    form = MainGUI()
    form.show()
    app.exit(app.exec_())

if __name__ == '__main__':
    main()

The console output of the above program when I run it and switch the combo box from "test 1" to "test 2" is as follows:

choice_changed
end choice changed

Process finished with exit code 139 (interrupted by signal 11: SIGSEGV)

The behavior I would like is for the frame to be regenerated entirely, without the error. Thanks!

Answer 1

If you want to remove a widget from a layout it is not enough to set a null parent since this does not remove it from the internal list that the layout has but only removes the c++ object causing the SIGSEGV. Instead you must use deleteLater() which if it ensures the correct elimination of the elements (for example the internal list of the layout).

def set_frame_controls(self):
    layout = self.ui.frame.layout()
    if layout is not None:
        for i in reversed(range(layout.count())):
            widget = layout.itemAt(i).widget()
            if widget is not None:
                widget.deleteLater()

    cbo_box = QComboBox()
    cbo_box.addItem("test 1")
    cbo_box.addItem("test 2")
    cbo_box.currentTextChanged.connect(self.choice_changed)
    layout.addWidget(cbo_box)