customDialog.py

class MainUI(QtWidgets.QMainWindow):
    def __init__(self, parent=getMainWindow()):
        super(MainUI, self).__init__(parent)

        list = ['apple', 'banana', 'pear']
        dialog = CustomDialog()
        dialog.setNamespaceCBox(list)
        
        # only when self.accept() is returned
        # need close event to return self.close()
        if dialog.exec_():
            print('accepted')
        else:
            print('not accepted')
            
        text = dialog.getText()
        option = dialog.getCombo()

        print text, option
        

class CustomDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super(CustomDialog, self).__init__(parent)

        # Create widgets
        self.namespaceCBox = QtWidgets.QComboBox()
        self.namespaceEdit = QtWidgets.QLineEdit()
        self.acceptButton = QtWidgets.QPushButton("Confirm")

        # Create layout and add widgets
        layout = QtWidgets.QGridLayout()
        layout.addWidget(self.namespaceCBox, 0, 0)
        layout.addWidget(self.namespaceEdit, 0, 1)
        layout.addWidget(self.acceptButton, 1, 1)

        # Set dialog layout
        self.setLayout(layout)
        self.acceptButton.clicked.connect(self.onClickAccept)

    def closeEvent(self):
        self.close()
    
    def onClickAccept(self):
        self.accept()

    def getNamespaceEdit(self):
        return self.namespaceEdit.text()

    def getNamespaceCBox(self):
        return self.namespaceCBox.currentText()

    def setNamespaceCBox(self, items):
        self.namespaceCBox.addItems(items)