app.py

import sys
from PyQt5.QtWidgets import QApplication, QWidget, QLabel, QVBoxLayout

class HelloWindow(QWidget):
   def __init__(self):
      super().__init__()
      self.setWindowTitle("Hello PyQt5")
      self.setGeometry(100, 100, 300, 100)

      layout = QVBoxLayout()
      label = QLabel("Hello from PyQt5!")
      layout.addWidget(label)
      self.setLayout(layout)


if __name__ == "__main__":
   app = QApplication(sys.argv)
   window = HelloWindow()
   window.show()
   sys.exit(app.exec_())