Q:

Configuration celery with django: app.config_from_object('django.conf:settings') doesn't work

First of all, I am using Python 2.7, Django 1.9.12 and Celery 4.0.2 in my project. 
I am following "First steps with Django" Celery tutorial. 
This is my celeryapp.py:
from __future__ import absolute_import, unicode_literals
import os
from celery import Celery
import sys

sys.path.append('vagrant/nested_tree/nested_tree_project')

# set the default Django settings module for the 'celery' program. 
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'nested_tree_project.settings')

app = Celery('nested_tree_project', broker='amqp://localhost//')

# Using a string here means the worker don'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:global_settings', namespace='CELERY')

# Load task modules from all registered Django app configs. 
app.autodiscover_tasks()

I can make it work only this way, with global settings
app.config_from_object('django.conf:global_settings', namespace='CELERY')

And I actually cannot access my project settings.  If I use
'django.conf:settings'

I get an error when I start a celery worker
Traceback (most recent call last):
  File "/vagrant/nested_tree/venv/bin/celery", line 11, in <module>
    sys.exit(main())
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/__main__.py", line 14, in main
    _main()
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/celery.py", line 326, in main
    cmd.execute_from_commandline(argv)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/celery.py", line 488, in execute_from_com
mandline
    super(CeleryCommand, self).execute_from_commandline(argv)))
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/base.py", line 281, in execute_from_comma
ndline
    return self.handle_argv(self.prog_name, argv[1:])
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/celery.py", line 480, in handle_argv
    return self.execute(command, argv)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/celery.py", line 412, in execute
    ).run_from_argv(self.prog_name, argv[1:], command=argv[0])
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/worker.py", line 221, in run_from_argv
    return self(*args, **options)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/base.py", line 244, in __call__
    ret = self.run(*args, **kwargs)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/bin/worker.py", line 255, in run
    **kwargs)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/worker/worker.py", line 94, in __init__
    self.app.loader.init_worker()
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/loaders/base.py", line 116, in init_worker
    self.import_default_modules()
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/loaders/base.py", line 111, in import_default
_modules
    return [self.import_task_module(m) for m in self.default_modules]
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/loaders/base.py", line 97, in import_task_mod
ule
    return self.import_from_cwd(module)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/loaders/base.py", line 106, in import_from_cw
d
    package=package,
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/utils/imports.py", line 101, in import_from_c
wd
    return imp(module, package=package)
  File "/vagrant/nested_tree/venv/local/lib/python2.7/site-packages/celery/loaders/base.py", line 100, in import_module
    return importlib.import_module(module, package=package)
  File "/usr/lib/python2.7/importlib/__init__.py", line 32, in import_module
    raise TypeError("relative imports require the 'package' argument")

What am I doing wrong?  I've tried to run python shell from the same directory:
import sys, os, django
sys.path.append('vagrant/nested_tree/nested_tree_project')
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'nested_tree_project.settings')
django.setup()

It works just fine. 
In case it may be useful, this is my project hierarchy:

A:

Maybe Celery has been installed wrong.  I've created new virtual environment and it works now.