QWidget: Must construct a QApplication before a QWidget error in pyqt5 and selenium

Question

I want to run another python file when I press the button in the desktop program. However, when I press the button, I get the "QWidget: Must construct a QApplication before a QWidget" error.

Other python file is selenium library that works with webdriver. Data is collected in user.py.

masaustu.py

 import sys , os
 from PyQt5 import QtWidgets , QtGui
 from PyQt5.QtWidgets import QMainWindow , QApplication , QWidget , 
 QPushButton , QAction , QLineEdit , QMessageBox  
 from subprocess import Popen
 class App(QMainWindow):
    def on_click(self):
        usernameValue = self.username.text()
        passwordValue = self.password.text()
        nicknameValue = self.nickname.text()
        timeValue = self.time.text()
    

        QMessageBox.question(self, 'Message - pythonspot.com', "guduu: " + nicknameValue, QMessageBox.Ok, QMessageBox.Ok)
        Popen('python another.py')
    

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ex = App()
    sys.exit(app.exec_())

user.py

import importlib
from masaustu import App

App()
username = App.usernameValue
password = App.passwordValue
nickname = App.nicknameValue
time = App.timeValue

another.py works perfectly. But I could not connect with the desktop application. How can I do it ?