Qt for Python crashes accessing QObject::property

daljit97

So I am not sure this is a bug or something but I have spent quite sometime to figure this out but couldn't.
I have subclassed a QAbstractListModel using PySide2, however when I add an item to my model it crashes.
I figured out that the problem is in the following block of code:

    def data(self, index: QtCore.QModelIndex, role: int = ...):
        item = self.at(index.row()) # this should be a QObject
        pCount = item.metaObject().propertyCount() # check how many properties this item has
        # let's print the properties name
        for p in range(0, pCount):
            print(item.metaObject().property(p).name())
        # output was "getName" "getAge"
        roleName = self.m_displayRoleName if role is QtCore.Qt.DisplayRole else self.m_roles[role]
        if len(roleName) > 0:
            roleString = str(roleName, encoding='utf-8')
            if role is not self.baseRole():
                print(roleString) # this prints "getName"
                return item.property(roleString) # the program CRASHES while executing this line
            return item

    def at(self, idx):
        if 0 <= idx < len(self.m_items): # self.m_items is a list 
            return self.m_items[idx]

The function above implements the data method as required by any class which subclasses QAbstractListModel. I have tried to change the line that causes the error to:

return item.property("blablabla")

And now the crash is gone, but obviously the data is not obtained. Otherwise the program always crashes with the following output:

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

daljit97

@denni-0 said in Qt for Python crashes accessing QObject::property:

Okay unless PySide2 is doing some interesting naming conventions this code will not work because MyModelProvider() is not supplied

The provider is not necessary to the example so I deleted it. Anyway, the solution was that I was assigning the properties as QObjects while Python expected strings or int.
So changing @QtCore.Property(QtCore.QObject, constant=True) to @QtCore.Property(str, constant=True) worked.

daljit97

Yes, perhaps I should have done that earlier. The problem can be reproduced with the code below. I have 3 files
main.py:

import sys

from PySide2 import QtCore
from PySide2.QtWidgets import QApplication
from PySide2.QtCore import Qt, QCoreApplication, QObject, Slot
from PySide2.QtQml import QQmlApplicationEngine, QQmlContext



class MyItem(QObject):
    def __init__(self):
        super(MyItem, self).__init__()
        self.name = "John"
        self.age = 22

    @QtCore.Property(QtCore.QObject, constant=True)
    def getName(self):
        return self.name

    @QtCore.Property(QtCore.QObject, constant=True)
    def getAge(self):
        return self.age

if __name__ == '__main__':
    app = QApplication(sys.argv)
    item = MyItem()
    print(item.property("getName")) # the program crashes here
    QApplication.setAttribute(Qt.AA_EnableHighDpiScaling)
    QCoreApplication.setAttribute(Qt.AA_UseHighDpiPixmaps)

    engine = QQmlApplicationEngine()
    engine.load('qml/main.qml')
    sys.exit(app.exec_())

When you run the program it crashes

daljit97

@denni-0 said in Qt for Python crashes accessing QObject::property:

Okay unless PySide2 is doing some interesting naming conventions this code will not work because MyModelProvider() is not supplied

The provider is not necessary to the example so I deleted it. Anyway, the solution was that I was assigning the properties as QObjects while Python expected strings or int.
So changing @QtCore.Property(QtCore.QObject, constant=True) to @QtCore.Property(str, constant=True) worked.