# settings.py


INSTALLED_APPS = (
    'longerusername',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.admin',
    # ...
)


def _enable_conditional(application):
    global INSTALLED_APPS
    try:
        __import__(application)
        INSTALLED_APPS += (application,)
    except ImportError:
        pass

_enable_conditional('django_extensions')
_enable_conditional('debug_toolbar')