[Django]-How to run python script inside django project?

Django does not know this command since it is not listed anywhere. When you want to run a command with manage.py, use Django’s Admin Command.

EDIT Or if you really want to use django_extensions for some reason, use their GitHub docs as reference. There it states you need to add this app to INSTALLED_APPS:

INSTALLED_APPS = (
    ...
    'django_extensions',
    ...
)