Asynchronous call from QML to Python with callback 3

application.js

/*
 * This gist registers a custom QObject from Python into QML.
 * The QObject is called from QML, whereby Python performs an
 * expensive operation which, upon completion, emits a signal
 * which is then again handled from QML.
 *
 * See here for an alternative (that doesn't work)
 * https://gist.github.com/mottosso/aee134d71864bc8425e0
*/

"use strict";
/*global print, Service, Qt, appWindow*/


function MockHTTPRequest() {
    return Qt.createQmlObject("import Service 1.0; MockHTTPRequest {}",
                              appWindow, "MockHTTPRequest");
}

function onLoad() {
    var xhr = new MockHTTPRequest();
    xhr.requested.connect(function (reply) {
        print(reply);
    });

    xhr.request("POST", "/endpoint", {"data": "value"});

    print("request() was made");
}

main.py

import sys
import time
import threading

from PyQt5 import QtCore, QtGui, QtQml, QtQuick


class MockHTTPRequest(QtCore.QObject):
    requested = QtCore.pyqtSignal(QtCore.QVariant)

    @QtCore.pyqtSlot(str, str, QtCore.QVariant)
    def request(self, verb, endpoint, data):
        """Expensive call"""
        print verb, endpoint, data

        def thread():
            time.sleep(1)
            self.requested.emit("expensive result")

        threading.Thread(target=thread).start()

app = QtGui.QGuiApplication(sys.argv)
view = QtQuick.QQuickView()
context = view.rootContext()

QtQml.qmlRegisterType(MockHTTPRequest, 'Service', 1, 0, 'MockHTTPRequest')

view.setSource(QtCore.QUrl("main.qml"))
view.show()
app.exec_()

main.qml

import QtQuick 2.0

import "application.js" as App


Rectangle {
    id: appWindow
    width: 200
    height: 200
    Component.onCompleted: App.onLoad()
}