PyQt QWebkitWidgets not displaying web page when called from command line or object constructor

Question

from PyQt5 import QtCore, QtGui, QtWidgets
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *
from PyQt5.QtWebKit import *
from PyQt5.QtWebKitWidgets import *
from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow
import sys
import os

class Navigation(QWidget):
    def __init__(self):
        super().__init__()
        self.web = QWebView()
        self.web.settings().setAttribute(QWebSettings.
             JavascriptEnabled,True)
        #self.web.settings().setAttribute(QWebSettings.
        #    JavascriptCanOpenWindows, True)
        self.web.settings().setAttribute(QWebSettings.
            JSAC, True)

        #self.web.settings().setAttribute(QWebSettings.
        #DeveloperExtrasEnabled, True)
        filepath = os.path.join(
            os.path.dirname(__file__), 'MapSite.html')
        self.web.show()
        self.web.load(QUrl.fromLocalFile(filepath))

app = QApplication(sys.argv)
ex= Navigation()
app.exec_()

This PyQt program display a webpage only when run from IDLE for python3. When I run this program fom command line or make a Navigation class object by importing in other files, the webpage not displayed, just white screen

EDIT

pi@raspberrypi:~/RaspiCallSystem4 $ python3 navigation.py 
libEGL warning: DRI2: failed to authenticate
qt5ct: using qt5ct plugin
qt5ct: D-Bus system tray: no

when I execute from command line It give above output, web window starts but with white page only, running from IDLE executes smoothly

Answer 1

As the following answer indicates in some cases the command os.path.dirname(__file__) can return an empty string, and that's the case of the terminal, so there are 2 possible solutions:

filepath = os.path.join(os.path.dirname(os.path.abspath(__file__)), 'MapSite.html')

Or:

filepath = QDir.current().absoluteFilePath('MapSite.html')