Basic configuration¶

To configure Django with mod_python, first make sure you have Apache installed, with the mod_python module activated.

Then edit your httpd.conf file and add the following:

<Location "/mysite/">

SetHandler python-program

PythonHandler django.core.handlers.modpython

SetEnv DJANGO_SETTINGS_MODULE mysite.settings

PythonOption django.root /mysite

PythonDebug On

</Location>

...and replace mysite.settings with the Python import path to your Django project's settings file.

This tells Apache: "Use mod_python for any URL at or under '/mysite/', using the Django mod_python handler." It passes the value of DJANGO_SETTINGS_MODULE so mod_python knows which settings to use.

Because mod_python does not know we are serving this site from underneath the /mysite/ prefix, this value needs to be passed through to the mod_python handler in Django, via the PythonOption django.root ... line. The value set on that line (the last item) should match the string given in the <Location ...> directive. The effect of this is that Django will automatically strip the /mysite string from the front of any URLs before matching them against your URLConf patterns. If you later move your site to live under /mysite2, you will not have to change anything except the django.root option in the config file.

When using django.root you should make sure that what's left, after the prefix has been removed, begins with a slash. Your URLConf patterns that are expecting an initial slash will then work correctly. In the above example, since we want to send things like /mysite/admin/ to /admin/, we need to remove the string /mysite from the beginning, so that is the django.root value. It would be an error to use /mysite/ (with a trailing slash) in this case.

Note that we're using the <Location> directive, not the <Directory> directive. The latter is used for pointing at places on your filesystem, whereas <Location> points at places in the URL structure of a Web site. <Directory> would be meaningless here.

Also, if your Django project is not on the default PYTHONPATH for your computer, you'll have to tell mod_python where your project can be found:

<Location "/mysite/">

SetHandler python-program

PythonHandler django.core.handlers.modpython

SetEnv DJANGO_SETTINGS_MODULE mysite.settings

PythonOption django.root /mysite

PythonDebug On

PythonPath "['/path/to/project'] + sys.path"

</Location>

The value you use for PythonPath should include the parent directories of all the modules you are going to import in your application. It should also include the parent directory of the DJANGO_SETTINGS_MODULE location. This is exactly the same situation as setting the Python path for interactive usage. Whenever you try to import something, Python will run through all the directories in sys.path in turn, from first to last, and try to import from each directory until one succeeds.

An example might make this clearer. Suppose you have some applications under /usr/local/django-apps/ (for example, /usr/local/django-apps/weblog/ and so forth), your settings file is at /var/www/mysite/settings.py and you have specified DJANGO_SETTINGS_MODULE as in the above example. In this case, you would need to write your PythonPath directive as:

PythonPath "['/usr/local/django-apps/', '/var/www'] + sys.path"

With this path, import weblog and import mysite.settings will both work. If you had import blogroll in your code somewhere and blogroll lived under the weblog/ directory, you would also need to add /usr/local/django-apps/weblog/ to your PythonPath. Remember: the parent directories of anything you import directly must be on the Python path.

PythonPath "['c:/path/to/project'] + sys.path"

You can also add directives such as PythonAutoReload Off for performance. See the mod_python documentation for a full list of options.

Note that you should set PythonDebug Off on a production server. If you leave PythonDebug On, your users would see ugly (and revealing) Python tracebacks if something goes wrong within mod_python.

Restart Apache, and any request to /mysite/ or below will be served by Django. Note that Django's URLconfs won't trim the "/mysite/" -- they get passed the full URL.

When deploying Django sites on mod_python, you'll need to restart Apache each time you make changes to your Python code.

Multiple Django installations on the same Apache¶

It's entirely possible to run multiple Django installations on the same Apache instance. Just use VirtualHost for that, like so:

NameVirtualHost *



<VirtualHost *>

ServerName www.example.com

# ...

SetEnv DJANGO_SETTINGS_MODULE mysite.settings

</VirtualHost>



<VirtualHost *>

ServerName www2.example.com

# ...

SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings

</VirtualHost>

If you need to put two Django installations within the same VirtualHost (or in different VirtualHost blocks that share the same server name), you'll need to take a special precaution to ensure mod_python's cache doesn't mess things up. Use the PythonInterpreter directive to give different <Location> directives separate interpreters:

<VirtualHost *>

ServerName www.example.com

# ...

<Location "/something">

SetEnv DJANGO_SETTINGS_MODULE mysite.settings

PythonInterpreter mysite

</Location>



<Location "/otherthing">

SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings

PythonInterpreter othersite

</Location>

</VirtualHost>

The values of PythonInterpreter don't really matter, as long as they're different between the two Location blocks.

Running a development server with mod_python¶

If you use mod_python for your development server, you can avoid the hassle of having to restart the server each time you make code changes. Just set MaxRequestsPerChild 1 in your httpd.conf file to force Apache to reload everything for each request. But don't do that on a production server, or we'll revoke your Django privileges.

If you're the type of programmer who debugs using scattered print statements, note that print statements have no effect in mod_python; they don't appear in the Apache log, as one might expect. If you have the need to print debugging information in a mod_python setup, either do this:

assert False, the_value_i_want_to_see

Or add the debugging information to the template of your page.

Serving media files¶

Django doesn't serve media files itself; it leaves that job to whichever Web server you choose.

We recommend using a separate Web server -- i.e., one that's not also running Django -- for serving media. Here are some good choices:

• lighttpd
• TUX
• A stripped-down version of Apache

If, however, you have no option but to serve media files on the same Apache VirtualHost as Django, here's how you can turn off mod_python for a particular part of the site:

<Location "/media">

SetHandler None

</Location>

Just change Location to the root URL of your media files. You can also use <LocationMatch> to match a regular expression.

This example sets up Django at the site root but explicitly disables Django for the media subdirectory and any URL that ends with .jpg, .gif or .png:

<Location "/">

SetHandler python-program

PythonHandler django.core.handlers.modpython

SetEnv DJANGO_SETTINGS_MODULE mysite.settings

</Location>



<Location "/media">

SetHandler None

</Location>



<LocationMatch "".(jpg|gif|png)$">

SetHandler None

</LocationMatch>

Serving the admin files¶

Note that the Django development server automagically serves admin media files, but this is not the case when you use any other server arrangement. You're responsible for setting up Apache, or whichever media server you're using, to serve the admin files.

The admin files live in (django/contrib/admin/media) of the Django distribution.

Here are two recommended approaches:

1. Create a symbolic link to the admin media files from within your document root. This way, all of your Django-related files -- code and templates -- stay in one place, and you'll still be able to svn update your code to get the latest admin templates, if they change.
2. Or, copy the admin media files so that they live within your Apache document root.

Using "eggs" with mod_python¶

If you installed Django from a Python egg or are using eggs in your Django project, some extra configuration is required. Create an extra file in your project (or somewhere else) that contains something like the following:

import os

os.environ['PYTHON_EGG_CACHE'] = '/some/directory'

Here, /some/directory is a directory that the Apache webserver process can write to. It will be used as the location for any unpacking of code the eggs need to do.

Then you have to tell mod_python to import this file before doing anything else. This is done using the PythonImport directive to mod_python. You need to ensure that you have specified the PythonInterpreter directive to mod_python as described above (you need to do this even if you aren't serving multiple installations in this case). Then add the PythonImport line in the main server configuration (i.e., outside the Location or VirtualHost sections). For example:

PythonInterpreter my_django

PythonImport /path/to/my/project/file.py my_django

Note that you can use an absolute path here (or a normal dotted import path), as described in the mod_python manual. We use an absolute path in the above example because if any Python path modifications are required to access your project, they will not have been done at the time the PythonImport line is processed.

Error handling¶

When you use Apache/mod_python, errors will be caught by Django -- in other words, they won't propagate to the Apache level and won't appear in the Apache error_log.

The exception for this is if something is really wonky in your Django setup. In that case, you'll see an "Internal Server Error" page in your browser and the full Python traceback in your Apache error_log file. The error_log traceback is spread over multiple lines. (Yes, this is ugly and rather hard to read, but it's how mod_python does things.)

If you get a segmentation fault¶

If Apache causes a segmentation fault, there are two probable causes, neither of which has to do with Django itself.

1. It may be because your Python code is importing the "pyexpat" module, which may conflict with the version embedded in Apache. For full information, see Expat Causing Apache Crash.
2. It may be because you're running mod_python and mod_php in the same Apache instance, with MySQL as your database backend. In some cases, this causes a known mod_python issue due to version conflicts in PHP and the Python MySQL backend. There's full information in the mod_python FAQ entry.

If you continue to have problems setting up mod_python, a good thing to do is get a barebones mod_python site working, without the Django framework. This is an easy way to isolate mod_python-specific problems. Getting mod_python Working details this procedure.

The next step should be to edit your test code and add an import of any Django-specific code you're using -- your views, your models, your URLconf, your RSS configuration, etc. Put these imports in your test handler function and access your test URL in a browser. If this causes a crash, you've confirmed it's the importing of Django code that causes the problem. Gradually reduce the set of imports until it stops crashing, so as to find the specific module that causes the problem. Drop down further into modules and look into their imports, as necessary.

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