root/django/branches/sqlalchemy/docs/settings.txt

===============
Django settings
===============

A Django settings file contains all the configuration of your Django
installation. This document explains how settings work and which settings are
available.

The basics
==========

A settings file is just a Python module with module-level variables.

Here are a couple of example settings::

    DEBUG = False
    DEFAULT_FROM_EMAIL = 'webmaster@example.com'
    TEMPLATE_DIRS = ('/home/templates/mike', '/home/templates/john')

Because a settings file is a Python module, the following apply:

    * It doesn't allow for Python syntax errors.
    * It can assign settings dynamically using normal Python syntax.
      For example::

          MY_SETTING = [str(i) for i in range(30)]

    * It can import values from other settings files.

Designating the settings
========================

When you use Django, you have to tell it which settings you're using. Do this
by using an environment variable, ``DJANGO_SETTINGS_MODULE``.

The value of ``DJANGO_SETTINGS_MODULE`` should be in Python path syntax, e.g.
``mysite.settings``. Note that the settings module should be on the
Python `import search path`_.

.. _import search path: http://diveintopython.org/getting_to_know_python/everything_is_an_object.html

The django-admin.py utility
---------------------------

When using `django-admin.py`_, you can either set the environment variable
once, or explicitly pass in the settings module each time you run the utility.

Example (Unix Bash shell)::

    export DJANGO_SETTINGS_MODULE=mysite.settings
    django-admin.py runserver

Example (Windows shell)::

    set DJANGO_SETTINGS_MODULE=mysite.settings
    django-admin.py runserver

Use the ``--settings`` command-line argument to specify the settings manually::

    django-admin.py runserver --settings=mysite.settings

.. _django-admin.py: ../django_admin/

On the server (mod_python)
--------------------------

In your live server environment, you'll need to tell Apache/mod_python which
settings file to use. Do that with ``SetEnv``::

    <Location "/mysite/">
        SetHandler python-program
        PythonHandler django.core.handlers.modpython
        SetEnv DJANGO_SETTINGS_MODULE mysite.settings
    </Location>

Read the `Django mod_python documentation`_ for more information.

.. _Django mod_python documentation: ../modpython/

Default settings
================

A Django settings file doesn't have to define any settings if it doesn't need
to. Each setting has a sensible default value. These defaults live in the file
``django/conf/global_settings.py``.

Here's the algorithm Django uses in compiling settings:

    * Load settings from ``global_settings.py``.
    * Load settings from the specified settings file, overriding the global
      settings as necessary.

Note that a settings file should *not* import from ``global_settings``, because
that's redundant.

Seeing which settings you've changed
------------------------------------

There's an easy way to view which of your settings deviate from the default
settings. The command ``python manage.py diffsettings`` displays differences
between the current settings file and Django's default settings.

For more, see the `diffsettings documentation`_.

.. _diffsettings documentation: ../django_admin/#diffsettings

Using settings in Python code
=============================

In your Django apps, use settings by importing the object
``django.conf.settings``. Example::

    from django.conf import settings

    if settings.DEBUG:
        # Do something

Note that ``django.conf.settings`` isn't a module -- it's an object. So
importing individual settings is not possible::

    from django.conf.settings import DEBUG  # This won't work.

Also note that your code should *not* import from either ``global_settings`` or
your own settings file. ``django.conf.settings`` abstracts the concepts of
default settings and site-specific settings; it presents a single interface.
It also decouples the code that uses settings from the location of your
settings.

Altering settings at runtime
============================

You shouldn't alter settings in your applications at runtime. For example,
don't do this in a view::

    from django.conf import settings

    settings.DEBUG = True   # Don't do this!

The only place you should assign to settings is in a settings file.

Security
========

Because a settings file contains sensitive information, such as the database
password, you should make every attempt to limit access to it. For example,
change its file permissions so that only you and your Web server's user can
read it. This is especially important in a shared-hosting environment.

Available settings
==================

Here's a full list of all available settings, in alphabetical order, and their
default values.

ABSOLUTE_URL_OVERRIDES
----------------------

Default: ``{}`` (Empty dictionary)

A dictionary mapping ``"app_label.model_name"`` strings to functions that take
a model object and return its URL. This is a way of overriding
``get_absolute_url()`` methods on a per-installation basis. Example::

    ABSOLUTE_URL_OVERRIDES = {
        'blogs.Weblog': lambda o: "/blogs/%s/" % o.slug,
        'news.Story': lambda o: "/stories/%s/%s/" % (o.pub_year, o.slug),
    }

ADMIN_FOR
---------

Default: ``()`` (Empty list)

Used for admin-site settings modules, this should be a tuple of settings
modules (in the format ``'foo.bar.baz'``) for which this site is an admin.

The admin site uses this in its automatically-introspected documentation of
models, views and template tags.

ADMIN_MEDIA_PREFIX
------------------

Default: ``'/media/'``

The URL prefix for admin media -- CSS, JavaScript and images. Make sure to use
a trailing slash.

ADMINS
------

Default: ``()`` (Empty tuple)

A tuple that lists people who get code error notifications. When
``DEBUG=False`` and a view raises an exception, Django will e-mail these people
with the full exception information. Each member of the tuple should be a tuple
of (Full name, e-mail address). Example::

    (('John', 'john@example.com'), ('Mary', 'mary@example.com'))

ALLOWED_INCLUDE_ROOTS
---------------------

Default: ``()`` (Empty tuple)

A tuple of strings representing allowed prefixes for the ``{% ssi %}`` template
tag. This is a security measure, so that template authors can't access files
that they shouldn't be accessing.

For example, if ``ALLOWED_INCLUDE_ROOTS`` is ``('/home/html', '/var/www')``,
then ``{% ssi /home/html/foo.txt %}`` would work, but ``{% ssi /etc/passwd %}``
wouldn't.

APPEND_SLASH
------------

Default: ``True``

Whether to append trailing slashes to URLs. This is only used if
``CommonMiddleware`` is installed (see the `middleware docs`_). See also
``PREPEND_WWW``.

CACHE_BACKEND
-------------

Default: ``'simple://'``

The cache backend to use. See the `cache docs`_.

CACHE_MIDDLEWARE_KEY_PREFIX

Default: ``''`` (Empty string)

The cache key prefix that the cache middleware should use. See the
`cache docs`_.

DATABASE_ENGINE
---------------

Default: ``'postgresql'``

Which database backend to use. Either ``'postgresql'``, ``'mysql'``,
``'sqlite3'`` or ``'ado_mssql'``.

DATABASE_HOST
-------------

Default: ``''`` (Empty string)

Which host to use when connecting to the database. An empty string means
localhost. Not used with SQLite.

If this value starts with a forward slash (``'/'``) and you're using MySQL,
MySQL will connect via a Unix socket to the specified socket. For example::

    DATABASE_HOST = '/var/run/mysql'

If you're using MySQL and this value *doesn't* start with a forward slash, then
this value is assumed to be the host.

DATABASE_NAME
-------------

Default: ``''`` (Empty string)

The name of the database to use. For SQLite, it's the full path to the database
file.

DATABASE_OPTIONS
----------------

Default: ``{}`` (Empty dictionary)

Extra parameters to use when connecting to the database. Consult backend
module's document for available keywords.

DATABASE_PASSWORD
-----------------

Default: ``''`` (Empty string)

The password to use when connecting to the database. Not used with SQLite.

DATABASE_PORT
-------------

Default: ``''`` (Empty string)

The port to use when connecting to the database. An empty string means the
default port. Not used with SQLite.

DATABASE_USER
-------------

Default: ``''`` (Empty string)

The username to use when connecting to the database. Not used with SQLite.

DATE_FORMAT
-----------

Default: ``'N j, Y'`` (e.g. ``Feb. 4, 2003``)

The default formatting to use for date fields on Django admin change-list
pages -- and, possibly, by other parts of the system. See
`allowed date format strings`_.

See also DATETIME_FORMAT, TIME_FORMAT, YEAR_MONTH_FORMAT and MONTH_DAY_FORMAT.

.. _allowed date format strings: ../templates/#now

DATETIME_FORMAT
---------------

Default: ``'N j, Y, P'`` (e.g. ``Feb. 4, 2003, 4 p.m.``)

The default formatting to use for datetime fields on Django admin change-list
pages -- and, possibly, by other parts of the system. See
`allowed date format strings`_.

See also DATE_FORMAT, DATETIME_FORMAT, TIME_FORMAT, YEAR_MONTH_FORMAT and MONTH_DAY_FORMAT.

.. _allowed date format strings: ../templates/#now

DEBUG
-----

Default: ``False``

A boolean that turns on/off debug mode.

DEFAULT_CHARSET
---------------

Default: ``'utf-8'``

Default charset to use for all ``HttpResponse`` objects, if a MIME type isn't
manually specified. Used with ``DEFAULT_CONTENT_TYPE`` to construct the
``Content-Type`` header.

DEFAULT_CONTENT_TYPE
--------------------

Default: ``'text/html'``

Default content type to use for all ``HttpResponse`` objects, if a MIME type
isn't manually specified. Used with ``DEFAULT_CHARSET`` to construct the
``Content-Type`` header.

DEFAULT_FROM_EMAIL
------------------

Default: ``'webmaster@localhost'``

Default e-mail address to use for various automated correspondence from the
site manager(s).

DISALLOWED_USER_AGENTS
----------------------

Default: ``()`` (Empty tuple)

List of compiled regular expression objects representing User-Agent strings
that are not allowed to visit any page, systemwide. Use this for bad
robots/crawlers.  This is only used if ``CommonMiddleware`` is installed (see
the `middleware docs`_).

EMAIL_HOST
----------

Default: ``'localhost'``

The host to use for sending e-mail.

See also ``EMAIL_PORT``.

EMAIL_HOST_PASSWORD
-------------------

Default: ``''`` (Empty string)

Username to use for the SMTP server defined in ``EMAIL_HOST``. If empty,
Django won't attempt authentication.

See also ``EMAIL_HOST_USER``.

EMAIL_HOST_USER
---------------

Default: ``''`` (Empty string)

Username to use for the SMTP server defined in ``EMAIL_HOST``. If empty,
Django won't attempt authentication.

See also ``EMAIL_HOST_PASSWORD``.

EMAIL_PORT
----------

Default: ``25``

Port to use for the SMTP server defined in ``EMAIL_HOST``.

EMAIL_SUBJECT_PREFIX
--------------------

Default: ``'[Django] '``

Subject-line prefix for e-mail messages sent with ``django.core.mail.mail_admins``
or ``django.core.mail.mail_managers``. You'll probably want to include the
trailing space.

IGNORABLE_404_ENDS
------------------

Default: ``('mail.pl', 'mailform.pl', 'mail.cgi', 'mailform.cgi', 'favicon.ico', '.php')``

See also ``IGNORABLE_404_STARTS``.

IGNORABLE_404_STARTS
--------------------

Default: ``('/cgi-bin/', '/_vti_bin', '/_vti_inf')``

A tuple of strings that specify beginnings of URLs that should be ignored by
the 404 e-mailer. See ``SEND_BROKEN_LINK_EMAILS`` and ``IGNORABLE_404_ENDS``.

INSTALLED_APPS
--------------

Default: ``()`` (Empty tuple)

A tuple of strings designating all applications that are enabled in this Django
installation. Each string should be a full Python path to a Python package that
contains a Django application, as created by `django-admin.py startapp`_.

.. _django-admin.py startapp: ../django_admin/#startapp-appname

INTERNAL_IPS
------------

Default: ``()`` (Empty tuple)

A tuple of IP addresses, as strings, that:

    * See debug comments, when ``DEBUG`` is ``True``
    * Receive X headers if the ``XViewMiddleware`` is installed (see the
      `middleware docs`_)

JING_PATH
---------

Default: ``'/usr/bin/jing'``

Path to the "Jing" executable. Jing is a RELAX NG validator, and Django uses it
to validate each ``XMLField`` in your models.
See http://www.thaiopensource.com/relaxng/jing.html .

LANGUAGE_CODE
-------------

Default: ``'en-us'``

A string representing the language code for this installation. This should be
in standard language format. For example, U.S. English is ``"en-us"``. See the
`internationalization docs`_.

.. _internationalization docs: ../i18n/

LANGUAGES
---------

Default: A tuple of all available languages. Currently, this is::

    LANGUAGES = (
        ('ar', _('Arabic')),
        ('bn', _('Bengali')),
        ('cs', _('Czech')),
        ('cy', _('Welsh')),
        ('da', _('Danish')),
        ('de', _('German')),
        ('el', _('Greek')),
        ('en', _('English')),
        ('es', _('Spanish')),
        ('es_AR', _('Argentinean Spanish')),
        ('fr', _('French')),
        ('gl', _('Galician')),
        ('hu', _('Hungarian')),
        ('he', _('Hebrew')),
        ('is', _('Icelandic')),
        ('it', _('Italian')),
        ('ja', _('Japanese')),
        ('nl', _('Dutch')),
        ('no', _('Norwegian')),
        ('pt-br', _('Brazilian')),
        ('ro', _('Romanian')),
        ('ru', _('Russian')),
        ('sk', _('Slovak')),
        ('sl', _('Slovenian')),
        ('sr', _('Serbian')),
        ('sv', _('Swedish')),
        ('ta', _('Tamil')),
        ('uk', _('Ukrainian')),
        ('zh-cn', _('Simplified Chinese')),
        ('zh-tw', _('Traditional Chinese')),
    )

A tuple of two-tuples in the format (language code, language name). This
specifies which languages are available for language selection. See the
`internationalization docs`_ for details.

Generally, the default value should suffice. Only set this setting if you want
to restrict language selection to a subset of the Django-provided languages.

If you define a custom ``LANGUAGES`` setting, it's OK to mark the languages as
translation strings (as in the default value displayed above) -- but use a
"dummy" ``gettext()`` function, not the one in ``django.utils.translation``.
You should *never* import ``django.utils.translation`` from within your
settings file, because that module in itself depends on the settings, and that
would cause a circular import.

The solution is to use a "dummy" ``gettext()`` function. Here's a sample
settings file::

    gettext = lambda s: s

    LANGUAGES = (
        ('de', gettext('German')),
        ('en', gettext('English')),
    )

With this arrangement, ``make-messages.py`` will still find and mark these
strings for translation, but the translation won't happen at runtime -- so
you'll have to remember to wrap the languages in the *real* ``gettext()`` in
any code that uses ``LANGUAGES`` at runtime.

MANAGERS
--------

Default: ``()`` (Empty tuple)

A tuple in the same format as ``ADMINS`` that specifies who should get
broken-link notifications when ``SEND_BROKEN_LINK_EMAILS=True``.

MEDIA_ROOT
----------

Default: ``''`` (Empty string)

Absolute path to the directory that holds media for this installation.
Example: ``"/home/media/media.lawrence.com/"`` See also ``MEDIA_URL``.

MEDIA_URL
---------

Default: ``''`` (Empty string)

URL that handles the media served from ``MEDIA_ROOT``.
Example: ``"http://media.lawrence.com"``

Note that this should have a trailing slash if it has a path component.

Good: ``"http://www.example.com/static/"``
Bad: ``"http://www.example.com/static"``

MIDDLEWARE_CLASSES
------------------

Default::

    ("django.contrib.sessions.middleware.SessionMiddleware",
     "django.contrib.auth.middleware.AuthenticationMiddleware",
     "django.middleware.common.CommonMiddleware",
     "django.middleware.doc.XViewMiddleware")

A tuple of middleware classes to use. See the `middleware docs`_.

MONTH_DAY_FORMAT
----------------

Default: ``'F j'``

The default formatting to use for date fields on Django admin change-list
pages -- and, possibly, by other parts of the system -- in cases when only the
month and day are displayed.

For example, when a Django admin change-list page is being filtered by a date
drilldown, the header for a given day displays the day and month. Different
locales have different formats. For example, U.S. English would say
"January 1," whereas Spanish might say "1 Enero."

See `allowed date format strings`_. See also DATE_FORMAT, DATETIME_FORMAT,
TIME_FORMAT and YEAR_MONTH_FORMAT.

PREPEND_WWW
-----------

Default: ``False``

Whether to prepend the "www." subdomain to URLs that don't have it. This is
only used if ``CommonMiddleware`` is installed (see the `middleware docs`_).
See also ``APPEND_SLASH``.

PROFANITIES_LIST
----------------

A tuple of profanities, as strings, that will trigger a validation error when
the ``hasNoProfanities`` validator is called.

We don't list the default values here, because that would be profane. To see
the default values, see the file ``django/conf/global_settings.py``.

ROOT_URLCONF
------------

Default: Not defined

A string representing the full Python import path to your root URLconf. For example:
``"mydjangoapps.urls"``. See `How Django processes a request`_.

.. _How Django processes a request: ../url_dispatch/#how-django-processes-a-request

SECRET_KEY
----------

Default: ``''`` (Empty string)

A secret key for this particular Django installation. Used to provide a seed in
secret-key hashing algorithms. Set this to a random string -- the longer, the
better. ``django-admin.py startproject`` creates one automatically.

SEND_BROKEN_LINK_EMAILS
-----------------------

Default: ``False``

Whether to send an e-mail to the ``MANAGERS`` each time somebody visits a
Django-powered page that is 404ed with a non-empty referer (i.e., a broken
link). This is only used if ``CommonMiddleware`` is installed (see the
`middleware docs`_). See also ``IGNORABLE_404_STARTS`` and
``IGNORABLE_404_ENDS``.

SERVER_EMAIL
------------

Default: ``'root@localhost'``

The e-mail address that error messages come from, such as those sent to
``ADMINS`` and ``MANAGERS``.

SESSION_COOKIE_AGE
------------------

Default: ``1209600`` (2 weeks, in seconds)

The age of session cookies, in seconds. See the `session docs`_.

SESSION_COOKIE_DOMAIN
---------------------

Default: ``None``

The domain to use for session cookies. Set this to a string such as
``".lawrence.com"`` for cross-domain cookies, or use ``None`` for a standard
domain cookie. See the `session docs`_.

SESSION_COOKIE_NAME
-------------------

Default: ``'sessionid'``

The name of the cookie to use for sessions. This can be whatever you want.
See the `session docs`_.

SESSION_COOKIE_SECURE
---------------------

**New in Django development version**

Default: ``False``

Whether to use a secure cookie for the session cookie. If this is set to
``True``, the cookie will be marked as "secure," which means browsers may
ensure that the cookie is only sent under an HTTPS connection.
See the `session docs`_.

SESSION_EXPIRE_AT_BROWSER_CLOSE
-------------------------------

Default: ``False``

Whether to expire the session when the user closes his or her browser.
See the `session docs`_.

SESSION_SAVE_EVERY_REQUEST
--------------------------

Default: ``False``

Whether to save the session data on every request. See the `session docs`_.

SITE_ID
-------

Default: Not defined

The ID, as an integer, of the current site in the ``django_site`` database
table. This is used so that application data can hook into specific site(s)
and a single database can manage content for multiple sites.

See the `site framework docs`_.

.. _site framework docs: ../sites/

TEMPLATE_CONTEXT_PROCESSORS
---------------------------

Default::

    ("django.core.context_processors.auth",
    "django.core.context_processors.debug",
    "django.core.context_processors.i18n")

A tuple of callables that are used to populate the context in ``RequestContext``.
These callables take a request object as their argument and return a dictionary
of items to be merged into the context.

TEMPLATE_DEBUG
--------------

Default: ``False``

A boolean that turns on/off template debug mode. If this is ``True``, the fancy
error page will display a detailed report for any ``TemplateSyntaxError``. This
report contains the relevant snippet of the template, with the appropriate line
highlighted.

Note that Django only displays fancy error pages if ``DEBUG`` is ``True``, so
you'll want to set that to take advantage of this setting.

See also DEBUG.

TEMPLATE_DIRS
-------------

Default: ``()`` (Empty tuple)

List of locations of the template source files, in search order. Note that
these paths should use Unix-style forward slashes, even on Windows.

See the `template documentation`_.

TEMPLATE_LOADERS
----------------

Default: ``('django.template.loaders.filesystem.load_template_source',)``

A tuple of callables (as strings) that know how to import templates from
various sources. See the `template documentation`_.

TEMPLATE_STRING_IF_INVALID
--------------------------

Default: ``''`` (Empty string)

Output, as a string, that the template system should use for invalid (e.g.
misspelled) variables. See `How invalid variables are handled`_.

.. _How invalid variables are handled: ../templates_python/#how-invalid-variables-are-handled

TEST_RUNNER
-----------

**New in Django development version**

Default: ``'django.test.simple.run_tests'``

The name of the method to use for starting the test suite. See 
`Testing Django Applications`_.

.. _Testing Django Applications: ../testing/

TEST_DATABASE_NAME
------------------

**New in Django development version**

Default: ``None``

The name of database to use when running the test suite. If a value of 
``None`` is specified, the test database will use the name ``'test_' + settings.DATABASE_NAME``. See `Testing Django Applications`_.

.. _Testing Django Applications: ../testing/

TIME_FORMAT
-----------

Default: ``'P'`` (e.g. ``4 p.m.``)

The default formatting to use for time fields on Django admin change-list
pages -- and, possibly, by other parts of the system. See
`allowed date format strings`_.

See also DATE_FORMAT, DATETIME_FORMAT, TIME_FORMAT, YEAR_MONTH_FORMAT and
MONTH_DAY_FORMAT.

.. _allowed date format strings: ../templates/#now

TIME_ZONE
---------

Default: ``'America/Chicago'``

A string representing the time zone for this installation. `See available choices`_.
(Note that list of available choices lists more than one on the same line;
you'll want to use just one of the choices for a given time zone. For instance,
one line says ``'Europe/London GB GB-Eire'``, but you should use the first bit
of that -- ``'Europe/London'`` -- as your ``TIME_ZONE`` setting.)

Note that this is the time zone to which Django will convert all dates/times --
not necessarily the timezone of the server. For example, one server may serve
multiple Django-powered sites, each with a separate time-zone setting.

Normally, Django sets the ``os.environ['TZ']`` variable to the time zone you
specify in the  ``TIME_ZONE`` setting. Thus, all your views and models will
automatically operate in the correct time zone. However, if you're using the
manual configuration option (see below), Django will *not* touch the ``TZ``
environment variable, and it'll be up to you to ensure your processes are
running in the correct environment.

URL_VALIDATOR_USER_AGENT
------------------------

Default: ``Django/<version> (http://www.djangoproject.com/)``

The string to use as the ``User-Agent`` header when checking to see if URLs
exist (see the ``verify_exists`` option on URLField_).

.. _URLField: ../model_api/#urlfield

USE_ETAGS
---------

Default: ``False``

A boolean that specifies whether to output the "Etag" header. This saves
bandwidth but slows down performance. This is only used if ``CommonMiddleware``
is installed (see the `middleware docs`_).

USE_I18N
--------

Default: ``True``

A boolean that specifies whether Django's internationalization system should be
enabled. This provides an easy way to turn it off, for performance. If this is
set to ``False``, Django will make some optimizations so as not to load the
internationalization machinery.

YEAR_MONTH_FORMAT
-----------------

Default: ``'F Y'``

The default formatting to use for date fields on Django admin change-list
pages -- and, possibly, by other parts of the system -- in cases when only the
year and month are displayed.

For example, when a Django admin change-list page is being filtered by a date
drilldown, the header for a given month displays the month and the year.
Different locales have different formats. For example, U.S. English would say
"January 2006," whereas another locale might say "2006/January."

See `allowed date format strings`_. See also DATE_FORMAT, DATETIME_FORMAT,
TIME_FORMAT and MONTH_DAY_FORMAT.

.. _cache docs: ../cache/
.. _middleware docs: ../middleware/
.. _session docs: ../sessions/
.. _See available choices: http://www.postgresql.org/docs/8.1/static/datetime-keywords.html#DATETIME-TIMEZONE-SET-TABLE
.. _template documentation: ../templates_python/

Creating your own settings
==========================

There's nothing stopping you from creating your own settings, for your own
Django apps. Just follow these conventions:

    * Setting names are in all uppercase.
    * For settings that are sequences, use tuples instead of lists. This is
      purely for performance.
    * Don't reinvent an already-existing setting.

Using settings without setting DJANGO_SETTINGS_MODULE
=====================================================

In some cases, you might want to bypass the ``DJANGO_SETTINGS_MODULE``
environment variable. For example, if you're using the template system by
itself, you likely don't want to have to set up an environment variable
pointing to a settings module.

In these cases, you can configure Django's settings manually. Do this by
calling ``django.conf.settings.configure()``.

Example::

    from django.conf import settings

    settings.configure(DEBUG=True, TEMPLATE_DEBUG=True,
        TEMPLATE_DIRS=('/home/web-apps/myapp', '/home/web-apps/base'))

Pass ``configure()`` as many keyword arguments as you'd like, with each keyword
argument representing a setting and its value. Each argument name should be all
uppercase, with the same name as the settings described above. If a particular
setting is not passed to ``configure()`` and is needed at some later point,
Django will use the default setting value.

Configuring Django in this fashion is mostly necessary -- and, indeed,
recommended -- when you're using a piece of the framework inside a larger
application.

Consequently, when configured via ``settings.configure()``, Django will not
make any modifications to the process environment variables. (See the
explanation of ``TIME_ZONE``, above, for why this would normally occur.) It's
assumed that you're already in full control of your environment in these cases.

Custom default settings
-----------------------

If you'd like default values to come from somewhere other than
``django.conf.global_settings``, you can pass in a module or class that
provides the default settings as the ``default_settings`` argument (or as the
first positional argument) in the call to ``configure()``.

In this example, default settings are taken from ``myapp_defaults``, and the
``DEBUG`` setting is set to ``True``, regardless of its value in
``myapp_defaults``::

    from django.conf import settings
    from myapp import myapp_defaults

    settings.configure(default_settings=myapp_defaults, DEBUG=True)

The following example, which uses ``myapp_defaults`` as a positional argument,
is equivalent::

    settings.configure(myapp_defaults, DEBUG = True)

Normally, you will not need to override the defaults in this fashion. The
Django defaults are sufficiently tame that you can safely use them. Be aware
that if you do pass in a new default module, it entirely *replaces* the Django
defaults, so you must specify a value for every possible setting that might be
used in that code you are importing. Check in
``django.conf.settings.global_settings`` for the full list.

Either configure() or DJANGO_SETTINGS_MODULE is required
--------------------------------------------------------

If you're not setting the ``DJANGO_SETTINGS_MODULE`` environment variable, you
*must* call ``configure()`` at some point before using any code that reads
settings.

If you don't set ``DJANGO_SETTINGS_MODULE`` and don't call ``configure()``,
Django will raise an ``EnvironmentError`` exception the first time a setting
is accessed.

If you set ``DJANGO_SETTINGS_MODULE``, access settings values somehow, *then*
call ``configure()``, Django will raise an ``EnvironmentError`` saying settings
have already been configured.

Also, it's an error to call ``configure()`` more than once, or to call
``configure()`` after any setting has been accessed.

It boils down to this: Use exactly one of either ``configure()`` or
``DJANGO_SETTINGS_MODULE``. Not both, and not neither.