PyQt5-Minimal.py

import sys
from PyQt5.QtWidgets import QApplication
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QMainWindow, QDesktopWidget, QWidget, QVBoxLayout, QLabel, QLineEdit, QPushButton


class GUI(QMainWindow):

    def __init__(self):
        QMainWindow.__init__(self, flags=Qt.Window)

        self.setWindowTitle("Rechner")
        self.setFixedSize(300, 300)
        geometry = self.frameGeometry()
        geometry.moveCenter(QDesktopWidget().availableGeometry().center())
        self.move(geometry.topLeft())

        self.main_widget = QWidget()
        self.setCentralWidget(self.main_widget)

        self.main_layout = QVBoxLayout()
        self.main_widget.setLayout(self.main_layout)

        self.input_box_a = QLineEdit("4000")
        self.input_box_a.textChanged.connect(self.on_input_a_changed)
        self.main_layout.addWidget(QLabel("Input A:"))
        self.main_layout.addWidget(self.input_box_a)

        self.main_layout.addSpacing(20)

        self.input_box_b = QLineEdit("12")
        self.input_box_b.textChanged.connect(self.on_input_b_changed)
        self.main_layout.addWidget(QLabel("Input B:"))
        self.main_layout.addWidget(self.input_box_b)

        self.main_layout.addSpacing(20)

        self.result_box = QLineEdit()
        self.result_box.setReadOnly(True)
        self.main_layout.addWidget(QLabel("Ergebnis A · B:"))
        self.main_layout.addWidget(self.result_box)

        self.main_layout.addSpacing(20)

        self.close_button = QPushButton("Schließen")
        self.close_button.clicked.connect(self.on_close_clicked)
        self.main_layout.addWidget(self.close_button)

        self.main_layout.addStretch()

        self.update_result()

    def update_result(self):
        try:
            a = int(self.input_box_a.text())
        except ValueError:
            a = 0

        try:
            b = int(self.input_box_b.text())
        except ValueError:
            b = 0

        x = a * b
        print(f"Neuberechnung: a = {a}, b = {b}, x = {x}\n")

        self.result_box.setText(str(x))

    def on_input_a_changed(self, text):
        print(f"Input A wurde geändert: {text}")
        self.update_result()

    def on_input_b_changed(self, text):
        print(f"Input B wurde geändert: {text}")
        self.update_result()

    def on_close_clicked(self):
        self.close()


def main():
    app = QApplication(sys.argv)

    gui = GUI()
    gui.show()

    rc = app.exec()
    sys.exit(rc)


if __name__ == "__main__":
    main()