One more post about my experience coding a Django application for Facebook. Let's discuss a little about correctly setting up Apache and mod_python.

Most of the steps are very well described on Django's documentation but you may need a few more details. Let's see.

The importance of PYTHONPATH

According to the official documentation this is what you need on your Apache's site configuration to setup Django:

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

Obviously PythonDebug On should not appear, or should be set to Off, on a production environment.

The lines above assume that your Django project is called mysite and the site is on http://example.com/mysite. And even if the documentation mentions how to handle PYTHONPATH via mod_python I didn't have a clear picture of the whole thing after running my first failed tests.

I decided to setup a site dedicated just to my Django project, you can use name based or IP based virtual hosts on Apache, and I want to access it from the root: http://example.com/. Also, I store all my Python related stuff in /home/alexis/python-work hence the project will be at /home/alexis/python-work/project and its only application below it: /home/alexis/python-work/project/app.

I know there are better ways to organize reusable applications on Django, as James Bennett suggests, but for my project a traditional project/app structure was enough. Anyway, the following ideas can be applied to any setup. Let's see all the lines I use on Apache to setup a Django site:

<VirtualHost 192.168.0.180>
ServerName example.com
ServerAdmin alexis@example.com
<Location "/">
SetHandler python-program
PythonHandler django.core.handlers.modpython
SetEnv DJANGO_SETTINGS_MODULE project.settings
PythonDebug On
PythonPath "['/home/alexis/python-work', '/home/alexis/python-work/project'] + sys.path"
</Location>
</VirtualHost>

The IP on VirtualHost, 192.168.0.180, is the private one I'll be using for this site. I've also added 192.168.0.180 example.com in /etc/hosts to avoid changes on the DNS server, something you should do on production.

project.settings refers to the settings.py file inside the /home/alexis/python-work/project directory.

I've also removed PythonOption django.root /mysite because this site sits on root, Location "/", and there's no need to specify a subdirectory.

And the most important part:

PythonPath "['/home/alexis/python-work', '/home/alexis/python-work/project'] + sys.path"

This is how you add paths to PYTHONPATH via mod_python. Notice we have two paths, one for the parent directory and another for the project, both are needed to get all your imports right. Django's documentation highlights this:

Remember: the parent directories of anything you import directly must be on the Python path.

After adding these changes you should restart Apache, or possibly just reload, and be able to access your Django site at http://example.com/.

And everything else?

I haven't touched yet on how to serve static files on a production environment, something I'm doing with a combination of Lighty, mod_proxy and Apache, or the initial setup of a Linux server, Ubuntu in my case, with Apache and mod_python, so there's a lot more coming about Django applications deployment. Stay tuned.