Выполнение всех процессов при отмеченных QCheckBox

Как сделать так, чтобы выполнялись процессы отмеченных checkBox?
У меня код, который выводит в lineEdit номера соответствующих checkBox, по отдельности работает, но когда отмечаю несколько, то выводит меньший номер среди отмеченных, как сделать так, чтобы выводились все отмеченные значения?

Код формы окна:

from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(152, 237)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.verticalLayout = QtWidgets.QVBoxLayout(self.centralwidget)
        self.verticalLayout.setObjectName("verticalLayout")
        self.checkBox = QtWidgets.QCheckBox(self.centralwidget)
        self.checkBox.setObjectName("checkBox")
        self.verticalLayout.addWidget(self.checkBox)
        self.checkBox_2 = QtWidgets.QCheckBox(self.centralwidget)
        self.checkBox_2.setObjectName("checkBox_2")
        self.verticalLayout.addWidget(self.checkBox_2)
        self.checkBox_3 = QtWidgets.QCheckBox(self.centralwidget)
        self.checkBox_3.setObjectName("checkBox_3")
        self.verticalLayout.addWidget(self.checkBox_3)
        self.checkBox_4 = QtWidgets.QCheckBox(self.centralwidget)
        self.checkBox_4.setObjectName("checkBox_4")
        self.verticalLayout.addWidget(self.checkBox_4)
        self.pushButton = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton.setObjectName("pushButton")
        self.verticalLayout.addWidget(self.pushButton)
        self.lineEdit = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit.setObjectName("lineEdit")
        self.verticalLayout.addWidget(self.lineEdit)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 152, 21))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.checkBox.setText(_translate("MainWindow", "A"))
        self.checkBox_2.setText(_translate("MainWindow", "B"))
        self.checkBox_3.setText(_translate("MainWindow", "C"))
        self.checkBox_4.setText(_translate("MainWindow", "D"))
        self.pushButton.setText(_translate("MainWindow", "PushButton"))
        

if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

Код:

from PyQt5 import QtWidgets
from PyQt5.QtWidgets import *
import untitled_ui
from untitled_ui import Ui_MainWindow


class Test(QtWidgets.QMainWindow, untitled_ui.Ui_MainWindow):
    def __init__(self, parent=None):
        super(Test, self).__init__(parent)

        self.setupUi(self)
        self.pushButton.clicked.connect(self.action)

    def action(self):
        # QMessageBox.information(self, 'test', 'test')
        first = []
        second  = []
        third = []
        fourth = []
        if self.checkBox.isChecked():
            first.append('1')
        elif self.checkBox_2.isChecked():
            second.append('2')

        elif self.checkBox_3.isChecked():
            third.append('3')
        elif self.checkBox_4.isChecked():
            fourth.append('4')
        else:
            self.lineEdit.setText('NoNe')
        self.lineEdit.setText(f'{first},{second},{third},{fourth}')


if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    MainWindow = QtWidgets.QMainWindow()
    ui = Test()
    ui.show()
    sys.exit(app.exec_())