from PyQt5.QtWidgets import QDialog, QDialogButtonBox, QVBoxLayout, QLabel


class CustomDialog(QDialog):

    def __init__(self, parent=None):
        super().__init__(parent)

        self.setWindowTitle("Hello!")

        buttons = QDialogButtonBox.Ok | QDialogButtonBox.Cancel

        self.buttonBox = QDialogButtonBox(buttons)
        self.buttonBox.accepted.connect(self.accepted)
        self.buttonBox.rejected.connect(self.rejected)

        self.layout = QVBoxLayout()
        message = QLabel("Something happened, is that OK?")
        self.layout.addWidget(message)
        self.layout.addWidget(self.buttonBox)
        self.setLayout(self.layout)