QQmlComponent.create() item ownership PyQt bug example

qmlcomponent_obj_ownership.py

import sys
import textwrap

import sip

from PyQt5.QtQml import QQmlEngine, QQmlComponent
from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import QUrl


def main():
    app = QApplication(sys.argv)

    qml_engine = QQmlEngine()

    component = QQmlComponent(qml_engine)
    component.setData(textwrap.dedent("""\
        import QtQuick 2.0

        Rectangle {
            Component.onCompleted: {
                console.log("created");
            }
            Component.onDestruction: {
                console.log("destroyed");
            }
        }
        """), QUrl())

    item = component.create()
    assert item.parent() is None

    # According to sip.dump(), item is owned by C++, but should be owned by
    # Python
    #sip.dump(item)
    # <PyQt5.QtCore.QObject object at 0x7f411e1c69d8>
    #     Reference count: 2
    #     Address of wrapped object: 0x22c0fb0
    #     Created by: C/C++
    #     To be destroyed by: C/C++
    #     Parent wrapper: NULL
    #     Next sibling wrapper: NULL
    #     Previous sibling wrapper: NULL
    #     First child wrapper: NULL

    # Explicit transfer of the ownership to Python fixes issue with not
    # destroyed QML item.
    #sip.transferback(item)

    del item
    # The QML item should be destroyed at this point, but it's not.

    input()

if __name__ == "__main__":
    main()