Django-Environ

Startup

manage.py

#!/usr/bin/env python
import os
import sys

if __name__ == "__main__":
    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "project.settings")

    from django.core.management import execute_from_command_line

    execute_from_command_line(sys.argv)

STARTUP

wsgi.py

import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "project.settings")

from django.core.wsgi import get_wsgi_application
application = get_wsgi_application()

DJANGO_SETTINGS_MODULE

Who exports?

Where?

When?

LOCAL settings

project/settings.py

DEBUG = False

SECRET_KEY = 'change-me'

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'mydatabase',
    }
}

try:
    from local_settings import *
except ImportError:
    pass

LOCAL SETTINGS

project/local_settings.py

DEBUG = True

SECRET_KEY = 'my-secret-key'

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': 'mydatabase',
    }
}

LOCAL SETTINGS

out of source control (.gitignore)

managed manually for environment-specific settings

hard to extend the base settings

project/local_settings.py

INSTALLED_APPS += ('debug_toolbar.apps.DebugToolbarConfig', ) # error

MIDDLEWARE_CLASSES += (
    'django.contrib.sessions.middleware.SessionMiddleware',
) # error

LOCAL SETTINGS

ANTI-PATTERN!

Jacob Kaplan-Moss

https://speakerdeck.com/jacobian/the-best-and-worst-of-django?slide=81

THE twelve-factor APP

inspired by Martin Fowler’s books Patterns of Enterprise Application Architecture and Refactoring

Apps sometimes store config as constants in the code.
This is a violation of twelve-factor, which requires strict separation of config from code.
Config varies substantially across deploys, code does not.

declarative formats for setup automation
maximum portability between execution environments
suitable for deployment on modern cloud platforms
minimize divergence between development and production
scale up without significant changes to tooling

THE TWELVE-FACTOR APP

Configuration

config is everything that is likely to vary between deploys
strict separation of config from code
stores config in environment variables

Django settings module is a weird mix of:

application configuration
environment-specific configuration

THE TWELVE-FACTOR APP

Backing Services

no distinction between local and third party services

THE TWELVE-FACTOR APP

Build, release, run

strict separation between the build, release, and run stages

The One True Way

Coined by Jacob Kaplan-Moss

reversing the import flow

import the base settings

from the environment-specific settings

project/settings/local.py

from .base import *

INSTALLED_APPS += ('debug_toolbar.apps.DebugToolbarConfig', )

MIDDLEWARE_CLASSES += (
    'debug_toolbar.middleware.DebugToolbarMiddleware',
)

THE TWO-SCOOPS WAY

book written by Daniel Greenfeld and Audrey Roy

Best Practices for Django projects

using Virtualenvs
environment-related requirements and settings
...

In practice

Multiple settings modules and

Multiple requirements files

for each environment.

manage.py

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "project.settings.development)

wsgi.py

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "project.settings.production")

run tests

python manage.py tests --settings=project.settings.tests

Read environment

The raw way

# project/settings/base.py

import os

DEBUG = bool(os.environ.get('DEBUG', False)) 

SECRET_KEY = os.environ['SECRET_KEY']

ALLOWED_HOSTS = os.environ['ALLOWED_HOSTS'].split()

Read environment

The semi-raw way

# project/settings/base.py
import os
from django.core.exceptions import ImproperlyConfigured

NOTSET = object()
def get_env_setting(setting, default=NOTSET):
  try:
    return os.environ[setting]
  except KeyError:
    if default is NOTSET:
      raise ImproperlyConfigured("Set the %s env variable" % setting)
    return default

DEBUG = bool(get_env_setting('DEBUG', Fals)) 
SECRET_KEY = get_env_setting('SECRET_KEY')
ALLOWED_HOSTS = get_env_setting('ALLOWED_HOSTS').split()

Read environment

Defaults

Casting

Validations

Errors Handling

Overrides

DJANGO-ENVIRON

defaults

import environ

env = environ.Env() 

DEBUG = env.bool('DEBUG', default=False)

# or

env = environ.Env(DEBUG=(bool, False),) 

DEBUG = env('DEBUG')

DJANGO-ENVIRON

VALIDATIONS & ERRORS HANDLING

import environ

env = environ.Env() 

# Raises ImproperlyConfigured exception if SITE_ID is not defined in os.environ or if os.environ['SITE_ID'] contains not valid int.
SITE_ID = env.int('SITE_ID')

# Raises ImproperlyConfigured exception if SECRET_KEY not in os.environ
SECRET_KEY = env('SECRET_KEY')

DJANGO-ENVIRON

Casting

import environ

env = environ.Env() 

DATABASES = {
    # Raises ImproperlyConfigured if DATABASE_URL not in os.environ
    'default': env.db(default='sqlite:////tmp/my-tmp-sqlite.db'),
}

dj-database-url
dj-search-url

django-cache-url

....

LOAD ENVIRONMENT

virtualenv postactivate/postdeactivate

export DEBUG=1
export SECRET_KEY=secure

supervisord

[program:my-project]
environment=DEBUG="1",SECRET_KEY="secure"

uwsgi

[uwsgi]
env=DEBUG=1
env=SECRET_KEY=secure

LOAD ENVIRONMENT

From files

joke2k/django-environ

jacobian/django-dotenv

jezdez/envdir

LOAD ENVIRONMENT

where?

manage.py / wsgi.py

settings/base.py

LINKS

django-stop-writing-settings-files

djangoproject wiki SplitSettings

easier-12-factor-django
django-environ docs