hello.py

import sys
from PyQt5.QtWidgets import (
    QApplication,
    QMainWindow,
    QPlainTextEdit,
    QVBoxLayout,
    QWidget
)


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.resize(320, 240)
        self.setWindowTitle('Qute Text Editor')
        self.setCentralWidget(QWidget())
        self.centralWidget().setLayout(QVBoxLayout())
        self.editor = QPlainTextEdit(self.centralWidget())
        self.centralWidget().layout().addWidget(self.editor)


def app_main(args):
    app = QApplication(sys.argv)
    win = MainWindow()
    win.show()
    return app.exec_()


if __name__ == '__main__':
    sys.exit(app_main(sys.argv))