How does it work, the naming convention for Django INSTALLED_APPS?

That is the Application Configuration feature, new to Django 1.7.

Basically, now you can list in INSTALLED_APPS either the module that contains the application or a class that derives from django.apps.AppConfig and defines the behavior of the application.

This feature provides several advantages:

• Apps can be configured more easily, and even subclassed for customization.
• You can have several apps in the same module.

Application modules can define the special module variable default_app_config to specify the name of their AppConfig, so that they can use the new features without having to specify the full name of that class in INSTALLED_APPS. But this is a backwards compatibility feature and new applications are recommended to write the full AppConfig name.

Anyway, most django/contrib apps use that default_app_config, for compatibility with old configurations. See for example the file django/contrib/messages/__init__.py is just:

from django.contrib.messages.api import *
from django.contrib.messages.constants import *

default_app_config = 'django.contrib.messages.apps.MessagesConfig'

So, adding it up, per OP request:

• If you add in INSTALLED_APPS the typename foo.apps.FooConfig, then that class will be used to setup the foo app, 1.7 style (recommended).

• If you add in INSTALLED_APPS the plain name foo, then:

  • if there is a variable foo.default_app_config this class will be used to setup the foo app, 1.7 style. Most (all?) the standard Django apps have this variable, so that you don’t need to change your INSTALLED_APPS when you upgrade from Django-1.6 to Django-1.7.
  • if there is not such a variable, then the 1.6 style application will be used, with default values for the advanced configuration options.