pyqtSlot and garbage collector problem examples

main.qml

import QtQuick 2.9
import QtQuick.Controls 2.2

ApplicationWindow {
    id: main_window
    visible: true
    width: 500
    height: 500

    Item {
        id: item1

        Component.onCompleted: {
            var lista = prueba_manager.data_request()
            console.log(lista)
            console.log(lista[0])
            console.log(lista[0]['text'])
        }
    }
}

main1.py

import sys

from PyQt5.QtCore import QObject, pyqtSlot, pyqtProperty
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine, QQmlListProperty


class PruebaObject(QObject):
    def __init__(self, text):
        QObject.__init__(self)
        self._text = text

    @pyqtProperty('QString')
    def text(self):
        return self._text

    @text.setter
    def text(self, text):
        self._text = text


class PruebaManager(QObject):
    def __init__(self):
        QObject.__init__(self)

    @pyqtSlot(result=list)
    def data_request(self):
        aux = [PruebaObject('hi'), PruebaObject('bye')]
        return aux


def main():
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    prueba_manager = PruebaManager()
    engine.rootContext().setContextProperty("prueba_manager", prueba_manager)
    engine.load("main.qml")
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

main1_output.txt

qml: [,]
qml: null
file:.../main1.qml:17: TypeError: Cannot read property 'text' of null

main2.py

import sys

from PyQt5.QtCore import QObject, pyqtSlot, pyqtProperty
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine, QQmlListProperty


class PruebaObject(QObject):
    def __init__(self, text):
        QObject.__init__(self)
        self._text = text

    @pyqtProperty('QString')
    def text(self):
        return self._text

    @text.setter
    def text(self, text):
        self._text = text


class PruebaManager(QObject):
    def __init__(self):
        QObject.__init__(self)

    @pyqtSlot(result=QQmlListProperty)
    def data_request(self):
        aux = [PruebaObject('hi'), PruebaObject('bye')]
        return QQmlListProperty(PruebaObject, self, aux)


def main():
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    prueba_manager = PruebaManager()
    engine.rootContext().setContextProperty("prueba_manager", prueba_manager)
    engine.load("main.qml")
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

main2_output.txt

qml: QVariant(QQmlListProperty<QObject>)
qml: undefined
file:.../main1.qml:17: TypeError: Cannot read property 'text' of undefined

main3.py

import sys

from PyQt5.QtCore import QObject, pyqtSlot, pyqtProperty
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine, QQmlListProperty


class PruebaObject(QObject):
    def __init__(self, text):
        QObject.__init__(self)
        self._text = text

    @pyqtProperty('QString')
    def text(self):
        return self._text

    @text.setter
    def text(self, text):
        self._text = text


class PruebaManager(QObject):
    def __init__(self):
        QObject.__init__(self)

    @pyqtProperty(QQmlListProperty)
    def data_request(self):
        aux = [PruebaObject('hi'), PruebaObject('bye')]
        return QQmlListProperty(PruebaObject, self, aux)


def main():
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    prueba_manager = PruebaManager()
    engine.rootContext().setContextProperty("prueba_manager", prueba_manager)
    engine.load("main3.qml")
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

main3.qml

import QtQuick 2.9
import QtQuick.Controls 2.2

ApplicationWindow {
    id: main_window
    visible: true
    width: 500
    height: 500

    Item {
        id: item1

        Component.onCompleted: {
            var lista = prueba_manager.data_request
            console.log(lista)
            console.log(lista[0])
            console.log(lista[0]['text'])
        }
    }
}

main3_output.txt

qml: [object Object]
qml: PruebaObject(0x2714a50)
qml: hi

main4.py

import sys

from PyQt5.QtCore import QObject, pyqtSlot, pyqtProperty
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine, QQmlListProperty


class PruebaObject(QObject):
    def __init__(self, text):
        QObject.__init__(self)
        self._text = text

    @pyqtProperty('QString')
    def text(self):
        return self._text

    @text.setter
    def text(self, text):
        self._text = text


class PruebaManager(QObject):
    def __init__(self):
        QObject.__init__(self)

    @pyqtSlot(result=list)
    def data_request(self):
        self.aux = [PruebaObject('hi'), PruebaObject('bye')]
        return self.aux


def main():
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    prueba_manager = PruebaManager()
    engine.rootContext().setContextProperty("prueba_manager", prueba_manager)
    engine.load("main.qml")
    engine.quit.connect(app.quit)
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

main4_output.txt

qml: [PruebaObject(0x10dbde0),PruebaObject(0x10dbe90)]
qml: PruebaObject(0x10dbde0)
qml: hi