Python 2 doesn't support Django 2. On a Mac once you've installed Python 3 and Django 2 run the following command from shell to run your app while keeping path:
python3 manage.py runserver
Even if you have upgraded and are on a mac you will, by default, run Python 2 if you're entering the following command:
python manage.py runserver
The version of Django will then be wrong and you will see import errors for path