How to fix "TypeError................" in QtWidgets.QMessageBox for popup message in PyQT5

Question

I want to show popup info/warning/etc.. message to user, when user is submitting blank or incorrect info as Username and Password in PyQT5-GUI app.

I confused and i don't know where is the root cause of problem.

Windows 10 - 64 bit ___ Python 3.6 and 3.7 - 64 bit ____ PyQT5 - 5.11.3

class Ui_MainWindow(object):
def __init__(self):
  <skipped>
  self.btn_signin.clicked.connect(self.check_userPass) #### User/Pass checking.
  <skipped>

def check_userPass(self):  # an internal method/function from `Ui_MainWindow`.
  username = self.txt_user.text()  #a QlineEdit
  password = self.txt_pass.text()  #a QlineEdit
  if len(username) < 2  and  len(password) < 2:
    QtWidgets.QMessageBox.question(self, "Checkk", "Helllooo", QtWidgets.QMessageBox.Ok, QtWidgets.QMessageBox.Cancel)
    ###error for above line:
    ##Traceback (most recent call last):
    ##  File ".\demo_codes.py", line 215, in check_userPass
    ##    QtWidgets.QMessageBox.question(self, 'List manipulation', "Helllooo", QtWidgets.QMessageBox.Ok, QtWidgets.QMessageBox.Ok)
    ##TypeError: question(QWidget, str, str, buttons: Union[QMessageBox.StandardButtons, QMessageBox.StandardButton] = QMessageBox.StandardButtons(QMessageBox.Yes|QMessageBox.No), defaultButton: QMessageBox.StandardButton = QMessageBox.NoButton): argument 1 has unexpected type 'Ui_MainWindow'

    QtWidgets.QMessageBox.question("Checkk", "Helllooo", QtWidgets.QMessageBox.Ok, QtWidgets.QMessageBox.Cancel)
    ###error for above line:
    ##Traceback (most recent call last):
    ##  File ".\demo_codes.py", line 215, in check_userPass
    ##    QtWidgets.QMessageBox.question('List manipulation', "Helllooo", QtWidgets.QMessageBox.Ok, QtWidgets.QMessageBox.Ok)
    ##TypeError: question(QWidget, str, str, buttons: Union[QMessageBox.StandardButtons, QMessageBox.StandardButton] = QMessageBox.StandardButtons(QMessageBox.Yes|QMessageBox.No), defaultButton: QMessageBox.StandardButton = QMessageBox.NoButton): argument 1 has unexpected type 'str'

if __name__ == "__main__":
  import sys
  app = QtWidgets.QApplication(sys.argv)
  MainWindow = QtWidgets.QMainWindow()
  ui = Ui_MainWindow()
  #ui.setupUi(MainWindow) # i renamed `setupUi` to __init__.
  MainWindow.show()
  sys.exit(app.exec_())

Answer 1

Try it:

from PyQt5 import QtWidgets, QtCore, QtGui

class Ui_MainWindow(object):
#    def __init__(self):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(600, 350)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.txt_user = QtWidgets.QLineEdit(self.centralwidget)
        self.txt_user.setGeometry(QtCore.QRect(320, 130, 113, 20))
        self.txt_pass = QtWidgets.QLineEdit(self.centralwidget)
        self.txt_pass.setGeometry(QtCore.QRect(320, 170, 113, 20))

        self.btn_signin = QtWidgets.QPushButton("btn_signin\n`Fusion` style", self.centralwidget)
        self.btn_signin.setGeometry(QtCore.QRect(320, 200, 113, 50))        
        MainWindow.setCentralWidget(self.centralwidget)    

        # <skipped>
        self.btn_signin.clicked.connect(self.check_userPass) 
        # <skipped>

    def check_userPass(self):  
        username = self.txt_user.text()  #a QlineEdit
        password = self.txt_pass.text()  #a QlineEdit
        if len(username) < 2  and  len(password) < 2:
            """
#            QtWidgets.QMessageBox.question(
            QtWidgets.QMessageBox.information(
                 MainWindow,      # - self , + MainWindow  !!!
                "Checkk", 
                "Helllooo `Ali reza`", 
#                QtWidgets.QMessageBox.Ok, 
#                QtWidgets.QMessageBox.Cancel
                )
            """
# +++
            msg = QtWidgets.QMessageBox()
            msg.setIcon(QtWidgets.QMessageBox.Information)

            msg.setText("لطفا نام کاربری و رمزعبور خود را با دقت وارد نمایید")
            msg.setInformativeText("This is additional information")
            msg.setWindowTitle("MessageBox demo")
            msg.setDetailedText("The details are as follows:")
            msg.setStandardButtons(QtWidgets.QMessageBox.Ok ) #| QtWidgets.QMessageBox.Cancel)
            msg.buttonClicked.connect(self.msgbtn)

            retval = msg.exec_()                    # <<<---- !!!

            print("value of pressed message box button:", retval)
# +++
    def msgbtn(self, i):
        print( "Button pressed is:",i.text() )             


if __name__ == "__main__":
    import sys
    app = QtWidgets.QApplication(sys.argv)
    app.setStyle('Fusion')            # <<<--- convert app to FUSION style in win10

    MainWindow = QtWidgets.QMainWindow()

    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)   

    MainWindow.show()
    sys.exit(app.exec_())