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238 lines
9.0 KiB
Plaintext
238 lines
9.0 KiB
Plaintext
=================================
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How to use Django with mod_python
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=================================
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Apache_ with `mod_python`_ currently is the preferred setup for using Django
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on a production server.
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mod_python is similar to `mod_perl`_ : It embeds Python within Apache and loads
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Python code into memory when the server starts. Code stays in memory throughout
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the life of an Apache process, which leads to significant performance gains over
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other server arrangements.
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Django requires Apache 2.x and mod_python 3.x.
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We recommend you use Apache's `prefork MPM`_, as opposed to the `worker MPM`_.
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.. _Apache: http://httpd.apache.org/
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.. _mod_python: http://www.modpython.org/
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.. _mod_perl: http://perl.apache.org/
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.. _prefork MPM: http://httpd.apache.org/docs/2.2/mod/prefork.html
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.. _worker MPM: http://httpd.apache.org/docs/2.2/mod/worker.html
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Basic configuration
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===================
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To configure Django with mod_python, first make sure you have Apache installed,
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with the mod_python module activated.
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Then edit your ``httpd.conf`` file and add the following::
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<Location "/mysite/">
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SetHandler python-program
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PythonHandler django.core.handlers.modpython
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SetEnv DJANGO_SETTINGS_MODULE mysite.settings
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PythonDebug On
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</Location>
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...and replace ``mysite.settings`` with the Python path to your settings file.
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This tells Apache: "Use mod_python for any URL at or under '/mysite/', using the
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Django mod_python handler." It passes the value of ``DJANGO_SETTINGS_MODULE``
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so mod_python knows which settings to use.
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Also, if you've manually altered your ``PYTHONPATH`` to put your Django project
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on it, you'll need to tell mod_python::
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PythonPath "['/path/to/project'] + sys.path"
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You can also add directives such as ``PythonAutoReload Off`` for performance.
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See the `mod_python documentation`_ for a full list of options.
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Note that you should set ``PythonDebug Off`` on a production server. If you
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leave ``PythonDebug On``, your users would see ugly (and revealing) Python
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tracebacks if something goes wrong within mod_python.
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Restart Apache, and any request to /mysite/ or below will be served by Django.
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Note that Django's URLconfs won't trim the "/mysite/" -- they get passed the
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full URL.
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When deploying Django sites on mod_python, you'll need to restart Apache each
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time you make changes to your Python code.
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Multiple Django installations on the same Apache
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================================================
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It's entirely possible to run multiple Django installations on the same Apache
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instance. Just use ``VirtualHost`` for that, like so::
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NameVirtualHost *
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<VirtualHost *>
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ServerName www.example.com
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# ...
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SetEnv DJANGO_SETTINGS_MODULE mysite.settings
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</VirtualHost>
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<VirtualHost *>
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ServerName www2.example.com
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# ...
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SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings
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</VirtualHost>
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If you need to put two Django installations within the same ``VirtualHost``,
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you'll need to take a special precaution to ensure mod_python's cache doesn't
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mess things up. Use the ``PythonInterpreter`` directive to give different
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``<Location>`` directives separate interpreters::
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<VirtualHost *>
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ServerName www.example.com
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# ...
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<Location "/something">
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SetEnv DJANGO_SETTINGS_MODULE mysite.settings
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PythonInterpreter mysite
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</Location>
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<Location "/otherthing">
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SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings
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PythonInterpreter mysite_other
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</Location>
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</VirtualHost>
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The values of ``PythonInterpreter`` don't really matter, as long as they're
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different between the two ``Location`` blocks.
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Running a development server with mod_python
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============================================
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If you use mod_python for your development server, you can avoid the hassle of
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having to restart the server each time you make code changes. Just set
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``MaxRequestsPerChild 1`` in your ``httpd.conf`` file to force Apache to reload
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everything for each request. But don't do that on a production server, or we'll
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revoke your Django privileges.
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If you're the type of programmer who debugs using scattered ``print``
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statements, note that ``print`` statements have no effect in mod_python; they
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don't appear in the Apache log, as one might expect. If you have the need to
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print debugging information in a mod_python setup, either do this::
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assert False, the_value_i_want_to_see
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Or add the debugging information to the template of your page.
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.. _mod_python documentation: http://modpython.org/live/current/doc-html/directives.html
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Serving media files
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===================
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Django doesn't serve media files itself; it leaves that job to whichever Web
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server you choose.
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We recommend using a separate Web server -- i.e., one that's not also running
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Django -- for serving media. Here are some good choices:
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* lighttpd_
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* TUX_
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* A stripped-down version of Apache_
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If, however, you have no option but to serve media files on the same Apache
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``VirtualHost`` as Django, here's how you can turn off mod_python for a
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particular part of the site::
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<Location "/media/">
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SetHandler None
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</Location>
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Just change ``Location`` to the root URL of your media files. You can also use
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``<LocationMatch>`` to match a regular expression.
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This example sets up Django at the site root but explicitly disables Django for
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the ``media`` subdirectory and any URL that ends with ``.jpg``, ``.gif`` or
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``.png``::
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<Location "/">
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SetHandler python-program
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PythonHandler django.core.handlers.modpython
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SetEnv DJANGO_SETTINGS_MODULE mysite.settings
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</Location>
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<Location "media">
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SetHandler None
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</Location>
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<LocationMatch "\.(jpg|gif|png)$">
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SetHandler None
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</LocationMatch>
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.. _lighttpd: http://www.lighttpd.net/
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.. _TUX: http://en.wikipedia.org/wiki/TUX_web_server
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.. _Apache: http://httpd.apache.org/
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Serving the admin files
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=======================
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Note that the Django development server automagically serves admin media files,
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but this is not the case when you use any other server arrangement. You're
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responsible for setting up Apache, or whichever media server you're using, to
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serve the admin files.
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The admin files live in (``django/contrib/admin/media``) of the Django
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distribution.
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Here are two recommended approaches:
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1. Create a symbolic link to the admin media files from within your
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document root. This way, all of your Django-related files -- code
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**and** templates -- stay in one place, and you'll still be able to
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``svn update`` your code to get the latest admin templates, if they
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change.
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2. Or, copy the admin media files so that they live within your Apache
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document root.
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Error handling
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==============
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When you use Apache/mod_python, errors will be caught by Django -- in other
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words, they won't propagate to the Apache level and won't appear in the Apache
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``error_log``.
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The exception for this is if something is really wonky in your Django setup. In
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that case, you'll see an "Internal Server Error" page in your browser and the
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full Python traceback in your Apache ``error_log`` file. The ``error_log``
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traceback is spread over multiple lines. (Yes, this is ugly and rather hard to
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read, but it's how mod_python does things.)
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If you get a segmentation fault
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===============================
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If Apache causes a segmentation fault, there are two probable causes, neither
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of which has to do with Django itself.
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1. It may be because your Python code is importing the "pyexpat" module,
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which may conflict with the version embedded in Apache. For full
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information, see `Expat Causing Apache Crash`_.
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2. It may be because you're running mod_python and mod_php in the same
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Apache instance, with MySQL as your database backend. In some cases,
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this causes a known mod_python issue due to version conflicts in PHP and
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the Python MySQL backend. There's full information in the
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`mod_python FAQ entry`_.
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If you continue to have problems setting up mod_python, a good thing to do is
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get a barebones mod_python site working, without the Django framework. This is
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an easy way to isolate mod_python-specific problems. `Getting mod_python Working`_
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details this procedure.
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The next step should be to edit your test code and add an import of any
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Django-specific code you're using -- your views, your models, your URLconf,
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your RSS configuration, etc. Put these imports in your test handler function
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and access your test URL in a browser. If this causes a crash, you've confirmed
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it's the importing of Django code that causes the problem. Gradually reduce the
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set of imports until it stops crashing, so as to find the specific module that
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causes the problem. Drop down further into modules and look into their imports,
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as necessary.
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.. _Expat Causing Apache Crash: http://www.dscpl.com.au/articles/modpython-006.html
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.. _mod_python FAQ entry: http://modpython.org/FAQ/faqw.py?req=show&file=faq02.013.htp
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.. _Getting mod_python Working: http://www.dscpl.com.au/articles/modpython-001.html
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