whats the use of setting mysite.settings to DJANGO_SETTINGS_MODULE?

[Utpal Brahma]

under manage.py

////

#!/usr/bin/env python
import os
import sys

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings")
    try:
        from django.core.management import execute_from_command_line
    except ImportError:
        # The above import may fail for some other reason. Ensure that the
        # issue is really that Django is missing to avoid masking other
        # exceptions on Python 2.
        try:
            import django
        except ImportError:
            raise ImportError(
                "Couldn't import Django. Are you sure it's installed and "
                "available on your PYTHONPATH environment variable? Did you "
                "forget to activate a virtual environment?"
            )
        raise
    execute_from_command_line(sys.argv)

[Daniel Germano Travieso]

This is done so that when you run the script manage.py (that runs django commands) the module django imported by the script knows which project settings to use.

If you do not provide this, django will not recognize the apps you are developing, and will just recognize the default apps it comes bundled with.

https://docs.djangoproject.com/en/1.11/topics/settings/#envvar-DJANGO_SETTINGS_MODULE