PySide2: A Guide for Modern Qt Development

import sys
from PySide2.QtWidgets import QApplication, QLabel, QPushButton, QVBoxLayout, QWidget

class MyWindow(QWidget):
    def __init__(self):
        super().__init__()
        self.initUI()
    
    def initUI(self):
        self.label = QLabel('Clique no botão', self)
        self.button = QPushButton('Clique aqui', self)
        self.button.clicked.connect(self.button_clicked)
        
        layout = QVBoxLayout()
        layout.addWidget(self.label)
        layout.addWidget(self.button)
        self.setLayout(layout)
        
    def button_clicked(self):
        self.label.setText('Botão clicado!')
        
app = QApplication(sys.argv)
window = MyWindow()
window.show()
sys.exit(app.exec_())

from PySide2.QtCore import QUrl
from PySide2.QtQml import QQmlApplicationEngine

class Calculator:
    def __init__(self, parent=None):
        self.result = 0
    
    @Slot(int, int, result=int)
    def add(self, a, b):
        return a + b
    
app = QApplication([])
engine = QQmlApplicationEngine()

calculator = Calculator()
engine.rootContext().setContextProperty('calculator', calculator)
engine.load(QUrl.fromLocalFile('main.qml'))

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