How to stop Django "app not found" error?

When I run python ./manage.py sql grading my django site comes up with:

Error: App with label grading could not be found. Are you sure you INSTALLED_APPS setting is correct?

I have the app grading with __init__.py and everything, and my INSTALLED APPS is:

INSTALLED_APPS = (
    'django.contrib.auth',
    开发者_如何学JAVA'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.admin',
    'teachline.courses',
    'teachline.grading',
)

Why isn't this working?

---

Okay, I found what was going wrong. I ran python manage.py shell and tried to import teachline.grading.models. It turned out I had some problems with importing modules. I fixed those and now python manage.py sql grading works fine.

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Do you have a directory which contains teachline in your PYTHONPATH environment variable? It may be necessary to export PYTHONPATH="." to make things work.

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Does the file teachline/grading/__init__.py file exist in the pythonpath.

---

INSTALLED_APPS = (
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.sites',
    'django.contrib.admin',
    'teachline.courses',
    'teachline.grading',
)

Try to add just 'grading'

INSTALLED_APPS = (
        'django.contrib.auth',
        'django.contrib.contenttypes',
        'django.contrib.sessions',
        'django.contrib.sites',
        'django.contrib.admin',
        'courses',
        'grading',
    )