Exposing a Python Signal to QML 

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import sys

from PySide6.QtCore import QObject, Signal, Slot
from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine, QmlElement

# 1. Set the global variables

QML_IMPORT_NAME = 'examples.logger'
QML_IMPORT_MAJOR_VERSION = 1

# 2. Decorate the class with @QmlElement
#     and subclass QObject

@QmlElement
class Logger(QObject):
    
    # 3. Any signal declared here
    #    is available to Qml.
    
    messageLogged = Signal()
    
    @Slot(str)
    def log(self, message):
        print(message)
        self.messageLogged.emit()


if __name__ == '__main__':

    app = QGuiApplication(sys.argv)
    
    engine = QQmlApplicationEngine()
    engine.quit.connect(app.quit)
    engine.load('02_signal.qml')

    result = app.exec()
    del engine
    
    sys.exit(result)

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import QtQuick
import QtQuick.Controls
import QtQuick.Layouts

// 1. Use the QML_IMPORT_NAME value
//    to import the Logger class    

import examples.logger

ApplicationWindow {

    visible: true
    width: 400
    height:200
    title: "Template App"
    
    // 2. Create a Logger object
    
    Logger {
        id: logger
        // 3. the signal name follows a convention:
        //    messageLogged handler name becomes onMessageLogged 
        onMessageLogged: {
            console.log("The messageLogged signal emitted");
        }
    }

    RowLayout {
        
        anchors.fill: parent
            
        Button {
            text: "Click me!"

            Layout.fillWidth: true
            Layout.fillHeight: true
            
            font.pointSize:24
            font.bold: true
            
            onClicked: {
                logger.log("Log message")
            }
        }
    }
}