main.py

import os
import sys
from PySide6.QtCore import QObject, QUrl, Slot
from PySide6.QtGui import QGuiApplication
from PySide6.QtQuick import QQuickView

class RotateValue(QObject):
    def __init__(self):
        super(RotateValue,self).__init__()
        self.r = 0

    # If a slot returns a value, the return value type must be explicitly
    # defined in the decorator.
    @Slot(result=int)
    def val(self):
        self.r = self.r + 10
        return self.r

if __name__ == '__main__':
    app = QGuiApplication(sys.argv)
    view = QQuickView()

    rotatevalue = RotateValue()
    context = view.rootContext()
    context.setContextProperty("rotatevalue", rotatevalue)

    qmlFile = os.path.join(os.path.dirname(__file__), 'view.qml')
    view.setSource(QUrl.fromLocalFile(os.path.abspath(qmlFile)))
    if view.status() == QQuickView.Error:
        sys.exit(-1)
    view.show()
    res = app.exec_()
    # Deleting the view before it goes out of scope is required to make sure all child QML instances
    # are destroyed in the correct order.
    del view
    sys.exit(res)

view.qml

import QtQuick 2.0

Rectangle {
    id: page

    width: 500; height: 200
    color: "lightgray"

    Text {
        id: helloText
        text: "Hello world!"
        anchors.horizontalCenter: page.horizontalCenter
        y: 30
        font.pointSize: 24; font.bold: true
    }


    Rectangle {
        id: button
        width: 150; height: 40
        color: "darkgray"
        anchors.horizontalCenter: page.horizontalCenter
        y: 120
        MouseArea {
            id: buttonMouseArea
            objectName: "buttonMouseArea"
            anchors.fill: parent
            onClicked: {
                helloText.rotation = rotatevalue.val()
            }
        }
        Text {
            id: buttonText
            text: "Press me!"
            anchors.horizontalCenter: button.horizontalCenter
            anchors.verticalCenter: button.verticalCenter
            font.pointSize: 16
        }
    }
}