// main.py
from PyQt5.QtCore import pyqtSlot, QObject
from PyQt5.QtGui import QGuiApplication
from PyQt5.QtQml import QQmlApplicationEngine
import sys


class Bot(QObject):
    def __init__(self):
        super(Bot, self).__init__()

    @pyqtSlot(str)
    def say(self, what):
        print("Bot say: {}".format(what))


def main():
    """
    #include <QGuiApplication>
    #include <QQmlApplicationEngine>

    int main(int argc, char *argv[])
    {
        QGuiApplication app(argc, argv);

        QQmlApplicationEngine engine;
        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

        return app.exec();
    }
    """
    app = QGuiApplication(sys.argv)
    engine = QQmlApplicationEngine()
    context = engine.rootContext()
    bot = Bot()
    context.setContextProperty('Bot', bot)
    engine.load("Bot.qml")
    return app.exec_()


if __name__ == '__main__':
    sys.exit(main())

// Bot.qml
import QtQuick 2.5
import QtQuick.Controls 1.4


ApplicationWindow {
  id: appWindow

  Text {
    text: "Hello world"
  }

  Component.onCompleted: {
    visible = true
    Bot.say('Hi')
  }
}