[Django]-How to troubleshoot – ImportError: Could not import settings 'mysite.settings' when deploying django?

Ok, I figured out the problem myself, so I’ll answer my own question.
I find that there is no apache log or any other source of information to figure out what exactly is causing the Import Error. So I share my method below, as a more “rational” approach, in the hope that I can save somebody a few frustrating hours of randomly changing stuff.

For the record, here is the apache configuration that I used.

<Location "/mysite/">
    SetHandler python-program
    PythonHandler django.core.handlers.modpython
    SetEnv DJANGO_SETTINGS_MODULE mysite_django.settings
    PythonOption django.root /mysite
    PythonDebug On
    PythonPath "['/home/mysite/prg/mysite/mysite_django', '/home/mysite/prg/mysite'] + sys.path"
</Location>

I created a user “mysite” on the server, and the django settings.py is located in the (somewhat redundantly named) location /home/mysite/prg/mysite/mysite_django/settings.py.
I open an ssh channel to the server. In this case I use the very useful screen utility to switch quickly between users (but a second ssh channel would work just as well)

screen

Press Ctrl-A, Ctrl-C to create a new screen.
Now it’s important to see the permissions exactly as apache does, so I switch to the user that runs apache, which is www-data on debian systems:

sudo -i -u www-data

I’m going to try to import settings.py myself from the python environment:

python

>>> import os, sys
>>> print sys.path
... result omitted ...

This obviously should give you the standard sys.path without any of the “mysite” directories, because we’re running plain python. So I modified sys.path as follows. I copy-pasted directly from the apache configuration, to avoid typos:

>>> sys.path = ['/home/mysite/prg/mysite/mysite_django', '/home/mysite/prg/mysite'] + sys.path
>>> import mysite_django.settings
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named mysite_django.settings

As expected, I get the same error I already saw when loading my site in a browser. So I can replicate the problem within the python environment, that is a good thing. Clearly, the build path should be formed from the sys path entry ‘/home/mysite/prg/mysite’ plus the requested import path ‘mysite_django/settings.py’. So why is it not importing? Let’s make sure the given sys path entry actually exists

>>> os.path.exists (sys.path[0])
False

It doesn’t exist? Strange.

>>> os.path.exists ('/home')
True
>>> os.path.exists ('/home/mysite')
True
>>> os.path.exists ('/home/mysite/prg/')
True
>>> os.path.exists ('/home/mysite/prg/mysite')
True
>>> os.path.exists ('/home/mysite/prg/mysite/mysite_django')
False

Here I realize that there is something wrong with the permissions of mysite_django. Probably a left-over from all the random changes that I made. But actually, the problem is in the directory above, mysite, because that is where it tries to read the directory listing from. I switch to the superuser screen with Ctrl-A, Ctrl-N, and I use chmod to set the permissions of mysite so that they are the same as the last directory that succeeded:

$ ls -la /home/mysite/prg
total 12
drwxr-xr-x 3 mysite mysite 4096 2011-11-08 11:24 .
drwxr-xr-x 7 mysite mysite 4096 2011-11-08 14:56 ..
drwxr-xr-- 6 mysite mysite 4096 2011-11-08 11:35 mysite
$ chmod o+x /home/mysite/prg/mysite/
$ ls -la /home/mysite/prg
total 12
drwxr-xr-x 3 mysite mysite 4096 2011-11-08 11:24 .
drwxr-xr-x 7 mysite mysite 4096 2011-11-08 14:56 ..
drwxr-xr-x 6 mysite mysite 4096 2011-11-08 11:35 mysite

Switching back to the www-data screen with Ctrl-A, Ctrl-N:

>>> os.path.exists ('/home/mysite/prg/mysite/mysite_django')
True
>>> os.path.exists ('/home/mysite/prg/mysite/mysite_django/settings.py')
True

Now for the final test

>>> import mysite_django.settings
>>>

Yay! Success
We can even go further and test that django can load

>>> from django.core.management import setup_environ
>>> setup_environ(mysite_django.settings)
'/home/mysite/prg/mysite/mysite_django'

At this point the site was working again in my browser.

By following these steps, you can at least ensure that:

• there are no permission problems for settings.py for user www-data
• there are no mistakes in the PythonPath setting of your apache configuration
• there are no runtime errors when importing settings.py