gistfile1.txt

#!/usr/bin/env python

import sys

from PySide2.QtWidgets import QApplication, QWidget, QLabel, QVBoxLayout
from PySide2.QtGui import Qt

class HelloApplication(QApplication):
    def __init__(self, args):
        QApplication.__init__(self, args)
        self.remplir()
        self.exec_()

    def remplir(self):
        # Premiere fenetre
        self.win1 = QWidget()
        self.win1.resize(500, 250)
        self.win1.move(300, 50)
        self.win1.setWindowTitle("Premiere fenetre")

        self.label = QLabel()
        self.label.setText("Hello world")
        self.label.setAlignment(Qt.AlignCenter)

        # on prépare le contenu de win1
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.label)
        self.win1.setLayout(self.layout)

        self.label.show()
        self.win1.show()

if __name__ == "__main__":
    HelloApplication(sys.argv)