pyqt/basic/dialogs_start.py

import sys

from PyQt5.QtWidgets import QMainWindow, QPushButton, QApplication

from dialogs_2a import CustomDialog


class MainWindow(QMainWindow):

    def __init__(self):
        super().__init__()

        self.setWindowTitle("My First Window")

        button = QPushButton("Press me for a dialog!")
        button.clicked.connect(self.button_clicked)
        self.setCentralWidget(button)

    def button_clicked(self, is_checked):
        print("click", is_checked)

        dlg = CustomDialog(self)
        if dlg.exec_():
            print("Success!")
        else:
            print("Cancel!")


app = QApplication(sys.argv)
window = MainWindow()
window.show()
sys.exit(app.exec_())