testbed/django__django/docs/topics/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::

    ALLOWED_HOSTS = ["www.example.com"]
    DEBUG = False
    DEFAULT_FROM_EMAIL = "webmaster@example.com"

.. note::

    If you set :setting:`DEBUG` to ``False``, you also need to properly set
    the :setting:`ALLOWED_HOSTS` setting.

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.

.. _django-settings-module:

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

.. envvar:: DJANGO_SETTINGS_MODULE

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

The value of :envvar:`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: https://diveinto.org/python3/your-first-python-program.html#importsearchpath

The ``django-admin`` utility
----------------------------

When using :doc:`django-admin </ref/django-admin>`, 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):

.. code-block:: shell

    export DJANGO_SETTINGS_MODULE=mysite.settings
    django-admin runserver

Example (Windows shell):

.. code-block:: doscon

    set DJANGO_SETTINGS_MODULE=mysite.settings
    django-admin runserver

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

.. code-block:: shell

    django-admin runserver --settings=mysite.settings

.. _django-admin: ../django-admin/

On the server (``mod_wsgi``)
----------------------------

In your live server environment, you'll need to tell your WSGI
application what settings file to use. Do that with ``os.environ``::

    import os

    os.environ["DJANGO_SETTINGS_MODULE"] = "mysite.settings"

Read the :doc:`Django mod_wsgi documentation
</howto/deployment/wsgi/modwsgi>` for more information and other common
elements to a Django WSGI application.

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
module :source:`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
------------------------------------

The command ``python manage.py diffsettings`` displays differences between the
current settings file and Django's default settings.

For more, see the :djadmin:`diffsettings` documentation.

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
==================

For a full list of available settings, see the :doc:`settings reference </ref/settings>`.

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

There's nothing stopping you from creating your own settings, for your own
Django apps, but follow these guidelines:

* Setting names must be all uppercase.
* Don't reinvent an already-existing setting.

For settings that are sequences, Django itself uses lists, but this is only
a convention.

.. _settings-without-django-settings-module:

Using settings without setting :envvar:`DJANGO_SETTINGS_MODULE`
===============================================================

In some cases, you might want to bypass the :envvar:`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:

.. function:: django.conf.settings.configure(default_settings, **settings)

Example::

    from django.conf import settings

    settings.configure(DEBUG=True)

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
documentation of :setting:`TIME_ZONE` 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
:setting:`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 the code you are importing. Check in
``django.conf.settings.global_settings`` for the full list.

Either ``configure()`` or :envvar:`DJANGO_SETTINGS_MODULE` is required
----------------------------------------------------------------------

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

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

If you set :envvar:`DJANGO_SETTINGS_MODULE`, access settings values somehow,
*then* call ``configure()``, Django will raise a ``RuntimeError`` indicating
that settings have already been configured. There is a property for this
purpose:

.. attribute:: django.conf.settings.configured

For example::

    from django.conf import settings

    if not settings.configured:
        settings.configure(myapp_defaults, DEBUG=True)

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
:envvar:`DJANGO_SETTINGS_MODULE`. Not both, and not neither.

Calling ``django.setup()`` is required for "standalone" Django usage
--------------------------------------------------------------------

If you're using components of Django "standalone" -- for example, writing a
Python script which loads some Django templates and renders them, or uses the
ORM to fetch some data -- there's one more step you'll need in addition to
configuring settings.

After you've either set :envvar:`DJANGO_SETTINGS_MODULE` or called
``configure()``, you'll need to call :func:`django.setup()` to load your
settings and populate Django's application registry. For example::

    import django
    from django.conf import settings
    from myapp import myapp_defaults

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

    # Now this script or any imported module can use any part of Django it needs.
    from myapp import models

Note that calling ``django.setup()`` is only necessary if your code is truly
standalone. When invoked by your web server, or through :doc:`django-admin
</ref/django-admin>`, Django will handle this for you.

.. admonition:: ``django.setup()`` may only be called once.

    Therefore, avoid putting reusable application logic in standalone scripts
    so that you have to import from the script elsewhere in your application.
    If you can't avoid that, put the call to ``django.setup()`` inside an
    ``if`` block::

        if __name__ == "__main__":
            import django

            django.setup()

.. seealso::

    :doc:`The Settings Reference </ref/settings>`
        Contains the complete list of core and contrib app settings.