title: Celery + Django error: TypeError: 'Settings' object is not subscriptable
body: <p>I'm running into this issue and I have absolutely no idea where it comes from.</p>
  
  <p>I'm using exactly the same code provided in <a href="http://celery.readthedocs.org/en/latest/django/first-steps-with-django.html" rel="noreferrer">the Celery tutorial</a> except for the fact that I'm using the project directory also as my unique app directory (so, having models.py, views.py and adding 'proj' to INSTALLED_APPS).</p>
  
  <p>The weird part is, while trying this setup on my local machine, the error always appeared with every django command (migrate, shell...). Removing the virtualenv and reinstalling misteriously fixed it. Now, when pushing the app to Heroku I'm having the same issue and can't make it work.</p>
  
  <p>Any hints?
  Thanks!</p>
  
  <p>ps: Python 3.4.2, Django 1.8.4, Celery 3.1.18</p>
  
  <hr>
  
  <p>The error traceback:</p>
  
  <pre><code>Running `celery -A proj worker -l info` attached to terminal... up, run.7187
  Traceback (most recent call last):
    File "/app/.heroku/python/bin/celery", line 9, in &lt;module&gt;
      load_entry_point('celery==3.1.0', 'console_scripts', 'celery')()
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/__main__.py", line 29, in main
      main()
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/celery.py", line 80, in main
      cmd.execute_from_commandline(argv)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/celery.py", line 732, in execute_from_commandline
      super(CeleryCommand, self).execute_from_commandline(argv)))
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/base.py", line 299, in execute_from_commandline
      argv = self.setup_app_from_commandline(argv)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/base.py", line 429, in setup_app_from_commandline
      self.app = self.find_app(app)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/base.py", line 449, in find_app
      sym = self.symbol_by_name(app)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/bin/base.py", line 474, in symbol_by_name
      return symbol_by_name(name, imp=import_from_cwd)
    File "/app/.heroku/python/lib/python3.4/site-packages/kombu/utils/__init__.py", line 92, in symbol_by_name
      module = imp(module_name, package=package, **kwargs)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/utils/imports.py", line 101, in import_from_cwd
      return imp(module, package=package)
    File "/app/.heroku/python/lib/python3.4/importlib/__init__.py", line 109, in import_module
      return _bootstrap._gcd_import(name[level:], package, level)
    File "&lt;frozen importlib._bootstrap&gt;", line 2254, in _gcd_import
    File "&lt;frozen importlib._bootstrap&gt;", line 2237, in _find_and_load
    File "&lt;frozen importlib._bootstrap&gt;", line 2226, in _find_and_load_unlocked
    File "&lt;frozen importlib._bootstrap&gt;", line 1200, in _load_unlocked
    File "&lt;frozen importlib._bootstrap&gt;", line 1129, in _exec
    File "&lt;frozen importlib._bootstrap&gt;", line 1471, in exec_module
    File "&lt;frozen importlib._bootstrap&gt;", line 321, in _call_with_frames_removed
    File "/app/proj/__init__.py", line 5, in &lt;module&gt;
      from .celery import app as celery_app
    File "/app/proj/celery.py", line 17, in &lt;module&gt;
      app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/app/base.py", line 277, in autodiscover_tasks
      if self.conf.CELERY_FORCE_BILLIARD_LOGGING:
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/datastructures.py", line 336, in __getattr__
      return self[k]
    File "/app/.heroku/python/lib/python3.4/site-packages/celery/datastructures.py", line 458, in __getitem__
      return d[key]
    File "/app/.heroku/python/lib/python3.4/site-packages/django/utils/functional.py", line 227, in inner
      return func(self._wrapped, *args)
  TypeError: 'Settings' object is not subscriptable
  </code></pre>