django-configurations/docs/index.rst

.. include:: ../README.rst

Wait, what?
-----------

django-configurations helps you organize the configuration of your Django
project by providing the glue code to bridge between Django's module based
settings system and programming patterns like mixins_, facades_, factories_
and adapters_ that are useful for non-trivial configuration scenarios.

It allows you to use the native abilities of Python inheritance without the
side effects of module level namespaces that often lead to the unfortunate
use of the ``from foo import *`` anti-pattern.

.. _mixins: http://en.wikipedia.org/wiki/Mixin
.. _facades: http://en.wikipedia.org/wiki/Facade_pattern
.. _factories: http://en.wikipedia.org/wiki/Factory_method_pattern
.. _adapters: http://en.wikipedia.org/wiki/Adapter_pattern

Okay, how does it work?
-----------------------

Any subclass of the ``configurations.Configuration`` class will automatically
use the values of its class and instance attributes (including properties
and methods) to set module level variables of the same module -- that's
how Django will interface to the django-configurations based settings during
startup and also the reason why it requires you to use its own startup
functions.

That means when Django starts up django-configurations will have a look at
the ``DJANGO_CONFIGURATION`` environment variable to figure out which class
in the settings module (as defined by the ``DJANGO_SETTINGS_MODULE``
environment variable) should be used for the process. It then instantiates
the class defined with ``DJANGO_CONFIGURATION`` and copies the uppercase
attributes to the module level variables.

.. versionadded:: 0.2

Alternatively you can use the ``--configuration`` command line option that
django-configurations adds to all Django management commands. Behind the
scenes it will simply set the ``DJANGO_CONFIGURATION`` environement variable
so this is purely optional and just there to compliment the default
``--settings`` option that Django adds if you prefer that instead of setting
environment variables.

But isn't that magic?
---------------------

Yes, it looks like magic, but it's also maintainable and non-intrusive.
No monkey patching is needed to teach Django how to load settings via
django-configurations because it uses Python import hooks (`PEP 302`_)
behind the scenes.

.. _`PEP 302`: http://www.python.org/dev/peps/pep-0302/

Usage patterns
--------------

There are various configuration patterns that can be implemented with
django-configurations. The most common pattern is to have a base class
and various subclasses based on the enviroment they are supposed to be
used in, e.g. in production, staging and development.

Server specific settings
^^^^^^^^^^^^^^^^^^^^^^^^

For example, imagine you have a base setting class in your **settings.py**
file::

    from configurations import Settings

    class Base(Settings):
        TIME_ZONE = 'Europe/Berlin'

    class Dev(Base):
        DEBUG = True
        TEMPLATE_DEBUG = DEBUG

    class Prod(Base):
        TIME_ZONE = 'America/New_York'

You can now set the ``DJANGO_CONFIGURATION`` environment variable to one
of the class names you've defined, e.g. on your production server it
should be ``Prod``. In bash that would be::

    export DJANGO_SETTINGS_MODULE=mysite.settings
    export DJANGO_CONFIGURATION=Prod
    python manage.py runserver

Alternatively you can use the ``--configuration`` option when using Django
management commands along the lines of Django's default ``--settings``
command line option, e.g.::

    python manage.py runserver --settings=mysite.settings --configuration=Prod

Global settings defaults
^^^^^^^^^^^^^^^^^^^^^^^^

Every ``configurations.Settings`` subclass will automatically contain
Django's global settings as class attributes, so you can refer to them when
setting other values, e.g.::

    from configurations import Settings

    class Prod(Settings):
        TEMPLATE_CONTEXT_PROCESSORS = Settings.TEMPLATE_CONTEXT_PROCESSORS + (
                'django.core.context_processors.request',
            )

        @property
        def LANGUAGES(self):
            return Settings.LANGUAGES + (('tlh', 'Klingon'),)

Mixins
^^^^^^

You might want to apply some configuration values for each and every
project you're working on without having to repeat yourself. Just define
a few mixin you re-use multiple times::

    class FullPageCaching(object):
        USE_ETAGS = True

Then import that mixin class in your site settings module and use it with
a Settings class::

    from configurations import Settings

    class Prod(Settings, FullPageCaching):
        DEBUG = False
        # ...

Pristine methods
^^^^^^^^^^^^^^^^

.. versionadded:: 0.3

In case one of your settings itself need to be a callable, you need to
tell that django-configurations by using the ``pristinemethod`` decorator,
e.g.::

    from configurations import Settings, pristinemethod

    class Prod(Settings):

        @pristinemethod
        def ACCESS_FUNCTION(user):
            return user.is_staff

Lambdas work, too::

    from configurations import Settings, pristinemethod

    class Prod(Settings):
        ACCESS_FUNCTION = pristinemethod(lambda user: user.is_staff)

Setup methods
^^^^^^^^^^^^^

.. versionadded:: 0.3

If there is something required to be set up before or after the settings
loading happens, please override the ``pre_setup`` or ``post_setup``
class methods like so (don't forget to apply the Python ``@classmethod``
decorator::

    from configurations import Settings

    class Prod(Settings):
        # ...

        @classmethod
        def pre_setup(cls):
            if something.completely.different():
                cls.DEBUG = True

        @classmethod
        def post_setup(cls):
            print("done setting up! \o/")

As you can see above the ``pre_setup`` method can also be used to
programmatically change a class attribute of the settings class and it
will be taken into account when doing the rest of the settings setup.
Of course that won't work for ``post_setup`` since that's when the
settings setup is already done.

In fact you can easily do something unrelated to settings, like
connecting to a database::

    from configurations import Settings

    class Prod(Settings):
        # ...

        @classmethod
        def post_setup(cls):
            import mango
            mango.connect('enterprise')


.. warning::

    You could do the same by overriding the ``__init__`` method of your
    settings class but this may cause hard to debug errors because
    at the time the ``__init__`` method is called (during Django startup)
    the Django setting system isn't fully loaded yet.

    So anything you do in ``__init__`` that may require
    ``django.conf.settings`` or Django models there is a good chance it
    won't work. Use the ``post_setup`` method for that instead.

Alternatives
------------

Many thanks to those project that have previously solved these problems:

- The Pinax_ project for spearheading the efforts to extend the Django
  project metaphor with reusable project templates and a flexible
  configuration environment.

- `django-classbasedsettings`_ by Matthew Tretter for being the immediate
  inspiration for django-configurations.

.. _Pinax: http://pinaxproject.com
.. _`django-classbasedsettings`: https://github.com/matthewwithanm/django-classbasedsettings

Cookbook
--------

Celery
^^^^^^

Given Celery's way to load Django settings in worker processes you should
probably just add the following to the **begin** of your settings module::

    from configurations import importer
    importer.install()

That has the same effect as using the ``manage.py`` or ``wsgi.py`` utilities
mentioned above.

FastCGI
^^^^^^^

In case you use FastCGI for deploying Django (you really shouldn't) and aren't
allowed to us Django's runfcgi_ management command (that would automatically
handle the setup for your if you've followed the quickstart guide above), make
sure to use something like the following script::

    #!/usr/bin/env python

    import os
    import sys
     
    os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'mysite.settings')
    os.environ.setdefault('DJANGO_CONFIGURATION', 'MySiteSettings')

    from configurations.fastcgi import runfastcgi

    runfastcgi(method='threaded', daemonize='true')

As you can see django-configurations provides a helper module
``configurations.fastcgi`` that handles the setup of your configurations.

.. _runfcgi: https://docs.djangoproject.com/en/1.5/howto/deployment/fastcgi/

Bugs and feature requests
-------------------------

As always you mileage may vary, so please don't hesitate to send in feature
requests and bug reports at the usual place:

    https://github.com/jezdez/django-configurations/issues

Thanks!

.. include:: ../CHANGES.rst