How to use Django with Apache and mod_python¶
Support for mod_python has been deprecated, and will be removed in Django 1.5. If you are configuring a new deployment, you are strongly encouraged to consider using mod_wsgi or any of the other supported backends.
mod_python is similar to (and inspired by) mod_perl : It embeds Python within Apache and loads Python code into memory when the server starts. Code stays in memory throughout the life of an Apache process, which leads to significant performance gains over other server arrangements.
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.
Make sure that your Python source files' permissions are set such that the Apache user (usually named apache or httpd on most systems) will have read access to the files.
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.
If you're using Windows, we still recommended that you use forward slashes in the pathnames, even though Windows normally uses the backslash character as its native separator. Apache knows how to convert from the forward slash format to the native format, so this approach is portable and easier to read. (It avoids tricky problems with having to double-escape backslashes.)
This is valid even on a Windows system:
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 output to stdout will not appear in the Apache log and can even cause response errors.
If you have the need to print debugging information in a mod_python setup, you have a few options. You can print to stderr explicitly, like so:
print >> sys.stderr, 'debug text' sys.stderr.flush()
(note that stderr is buffered, so calling flush is necessary if you wish debugging information to be displayed promptly.)
A more compact approach is to use an assertion:
assert False, 'debug text'
Another alternative is to add 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:
If, however, you have no option but to serve media or static 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 and static subdirectories 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> <Location "/static"> SetHandler None </Location> <LocationMatch "\.(jpg|gif|png)$"> SetHandler None </LocationMatch>
Serving the admin files¶
Note that the Django development server automagically serves the static files of the admin app, 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/admin) of the Django distribution.
We strongly recommend using django.contrib.staticfiles to handle the admin files (this means using the collectstatic management command to collect the static files in STATIC_ROOT, and then configuring your webserver to serve STATIC_ROOT at STATIC_URL), but here are two other approaches:
- Create a symbolic link to the admin static files from within your document root.
- Or, copy the admin static 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 Web server 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.
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.
- 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.
- 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.
If you get a UnicodeEncodeError¶
If you're taking advantage of the internationalization features of Django (see Internationalization and localization) and you intend to allow users to upload files, you must ensure that the environment used to start Apache is configured to accept non-ASCII file names. If your environment is not correctly configured, you will trigger UnicodeEncodeError exceptions when calling functions like os.path() on filenames that contain non-ASCII characters.
To avoid these problems, the environment used to start Apache should contain settings analogous to the following:
export LANG='en_US.UTF-8' export LC_ALL='en_US.UTF-8'
Consult the documentation for your operating system for the appropriate syntax and location to put these configuration items; /etc/apache2/envvars is a common location on Unix platforms. Once you have added these statements to your environment, restart Apache.
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