Unable to run celery task that depends on Django code - django

Question

I seemingly have a bit of a catch 22 scenario when trying to run a celery task that depends on django code.
Celery code
from __future__ import absolute_import, unicode_literals
import os
from celery import Celery
from django.conf import settings
from celery import shared_task
from celery import task
from letters.send_write_letter_reminders import send_write_letter_reminders
# set the default Django settings module for the 'celery' program.
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'app_name.settings')
app = Celery('app_name')
# Using a string here means the worker doesn't have to serialize
# the configuration object to child processes.
# - namespace='CELERY' means all celery-related configuration keys
# should have a `CELERY_` prefix.
app.config_from_object('django.conf:settings', namespace='CELERY')
app.conf.timezone = 'Europe/London'
# Load task modules from all registered Django app configs.
app.autodiscover_tasks(settings.INSTALLED_APPS)
#app.task(bind=True, name='send_letter_reminders')
def send_letter_reminders(slug=None):
send_write_letter_reminders(slug=slug)
The problem I've run into is that with this line
from letters.send_write_letter_reminders import send_write_letter_reminders
With it I get:
django.core.exceptions.AppRegistryNotReady: Apps aren't loaded yet.
And the app server won't run, but without it I get:
NameError: name 'send_write_letter_reminders' is not defined
Obviously I'm missing something fundamental about how to run Celery and Django together, but I can't see it. Can anyone enlighten me as to what I've done wrong?
Update
I've come up with a hacky workaround for this, which involves moving the import to within the celery task. I realise this isn't best practice. Perhaps it might help explain what's going on though.
#app.task(bind=True, name='send_letter_reminders')
def send_letter_reminders(slug=None):
from letters.send_write_letter_reminders import send_write_letter_reminders
send_write_letter_reminders.send_write_letter_reminders(slug=slug)

Answer 1

Essentially, you can't do any django imports or import anything that relies on django until after you have executed the os.environ.setdefault line. The reason that you don't have to worry about this with anything run from manage.py is because the os.environ.setdefault is the first line of the manage.py. Essentially, just move the django.conf and letter import to below the os.environ.setdefault and things should work better. Depending on which version of django you are on, you may also need to explicitly call django.setup() after setting DJANGO_SETTINGS_MODULE to complete django setup.