main.py

import sys
from os.path import abspath, dirname, join

from PySide6.QtCore import QObject, Slot
from PySide6.QtGui import QGuiApplication
from PySide6.QtQml import QQmlApplicationEngine
from PySide6.QtQuickControls2 import QQuickStyle


class Bridge(QObject):

    @Slot(str, result=str)
    def getColor(self, s):
        if s.lower() == "red":
            return "#ef9a9a"
        elif s.lower() == "green":
            return "#a5d6a7"
        elif s.lower() == "blue":
            return "#90caf9"
        else:
            return "white"

    @Slot(float, result=int)
    def getSize(self, s):
        size = int(s * 34)
        if size <= 0:
            return 1
        else:
            return size

    @Slot(str, result=bool)
    def getItalic(self, s):
        if s.lower() == "italic":
            return True
        else:
            return False

    @Slot(str, result=bool)
    def getBold(self, s):
        if s.lower() == "bold":
            return True
        else:
            return False

    @Slot(str, result=bool)
    def getUnderline(self, s):
        if s.lower() == "underline":
            return True
        else:
            return False


if __name__ == '__main__':
    app = QGuiApplication(sys.argv)
    QQuickStyle.setStyle("Material")
    engine = QQmlApplicationEngine()

    # Instance of the Python object
    bridge = Bridge()

    # Expose the Python object to QML
    context = engine.rootContext()
    context.setContextProperty("con", bridge)

    # Get the path of the current directory, and then add the name
    # of the QML file, to load it.
    qmlFile = join(dirname(__file__), 'view.qml')
    engine.load(abspath(qmlFile))

    if not engine.rootObjects():
        sys.exit(-1)

    sys.exit(app.exec_())

view.qml

import QtQuick 2.0
import QtQuick.Layouts 1.11
import QtQuick.Controls 2.1
import QtQuick.Window 2.1
import QtQuick.Controls.Material 2.1

ApplicationWindow {
    id: page
    width: 800
    height: 400
    visible: true
    Material.theme: Material.Dark
    Material.accent: Material.Red

    GridLayout {
        id: grid
        columns: 2
        rows: 3

        ColumnLayout {
            spacing: 2
            Layout.columnSpan: 1
            Layout.preferredWidth: 400

            Text {
                id: leftlabel
                Layout.alignment: Qt.AlignHCenter
                color: "white"
                font.pointSize: 16
                text: "Qt for Python"
                Layout.preferredHeight: 100
                Material.accent: Material.Green
            }

            RadioButton {
                id: italic
                Layout.alignment: Qt.AlignLeft
                text: "Italic"
                onToggled: {
                    leftlabel.font.italic = con.getItalic(italic.text)
                    leftlabel.font.bold = con.getBold(italic.text)
                    leftlabel.font.underline = con.getUnderline(italic.text)

                }
            }
            RadioButton {
                id: bold
                Layout.alignment: Qt.AlignLeft
                text: "Bold"
                onToggled: {
                    leftlabel.font.italic = con.getItalic(bold.text)
                    leftlabel.font.bold = con.getBold(bold.text)
                    leftlabel.font.underline = con.getUnderline(bold.text)
                }
            }
            RadioButton {
                id: underline
                Layout.alignment: Qt.AlignLeft
                text: "Underline"
                onToggled: {
                    leftlabel.font.italic = con.getItalic(underline.text)
                    leftlabel.font.bold = con.getBold(underline.text)
                    leftlabel.font.underline = con.getUnderline(underline.text)
                }
            }
            RadioButton {
                id: noneradio
                Layout.alignment: Qt.AlignLeft
                text: "None"
                checked: true
                onToggled: {
                    leftlabel.font.italic = con.getItalic(noneradio.text)
                    leftlabel.font.bold = con.getBold(noneradio.text)
                    leftlabel.font.underline = con.getUnderline(noneradio.text)
                }
            }
        }

        ColumnLayout {
            id: rightcolumn
            spacing: 2
            Layout.columnSpan: 1
            Layout.preferredWidth: 400
            Layout.preferredHeight: 400
            Layout.fillWidth: true

            RowLayout {
                Layout.alignment: Qt.AlignVCenter | Qt.AlignHCenter


                Button {
                    id: red
                    text: "Red"
                    highlighted: true
                    Material.accent: Material.Red
                    onClicked: {
                        leftlabel.color = con.getColor(red.text)
                    }
                }
                Button {
                    id: green
                    text: "Green"
                    highlighted: true
                    Material.accent: Material.Green
                    onClicked: {
                        leftlabel.color = con.getColor(green.text)
                    }
                }
                Button {
                    id: blue
                    text: "Blue"
                    highlighted: true
                    Material.accent: Material.Blue
                    onClicked: {
                        leftlabel.color = con.getColor(blue.text)
                    }
                }
                Button {
                    id: nonebutton
                    text: "None"
                    highlighted: true
                    Material.accent: Material.BlueGrey
                    onClicked: {
                        leftlabel.color = con.getColor(nonebutton.text)
                    }
                }
            }
            RowLayout {
                Layout.fillWidth: true
                Layout.alignment: Qt.AlignVCenter | Qt.AlignHCenter
                Text {
                    id: rightlabel
                    color: "white"
                    Layout.alignment: Qt.AlignLeft
                    text: "Font size"
                    Material.accent: Material.White
                }
                Slider {
                    width: rightcolumn.width*0.6
                    Layout.alignment: Qt.AlignRight
                    id: slider
                    value: 0.5
                    onValueChanged: {
                        leftlabel.font.pointSize = con.getSize(value)
                    }
                }
            }
        }
    }
}