Settings from the Environment

Part of the JSON APIs section of Coddy's Django journey. Lesson 18 of 19.

Once your site is deployed, copied to a server on the internet, three settings must change. DEBUG = True shows your code and every URL pattern to anyone. SECRET_KEY signs sessions, so it cannot sit in code others read. ALLOWED_HOSTS lists the domains the site answers to.

The usual answer: read them from environment variables, values the server gives the program when it starts. os.environ.get(name, default) reads one, and the default is what your own computer gets:

PAGE_SIZE = int(os.environ.get("PAGE_SIZE", "20"))
MAINTENANCE = os.environ.get("MAINTENANCE", "no") == "yes"

A variable is always a string, so turn it into the type you need: int() for a number, a comparison for a real boolean, split(",") for a list. Pick safe defaults: a forgotten variable leaves DEBUG off.

Challenge

Medium

In mysite/settings.py, read from the environment:

SECRET_KEY from DJANGO_SECRET_KEY, default "django-insecure-change-me".
DEBUG: True only when DJANGO_DEBUG is "True".
ALLOWED_HOSTS from DJANGO_ALLOWED_HOSTS, comma-separated, default localhost,127.0.0.1.

Press Run, then open /nope/: with DEBUG off, the 404 page lists no URL patterns.

Try it yourself

from pathlib import Path

BASE_DIR = Path(__file__).resolve().parent.parent

SECRET_KEY = "django-insecure-change-me"
DEBUG = True
ALLOWED_HOSTS = []

INSTALLED_APPS = [
    "django.contrib.admin",
    "django.contrib.auth",
    "django.contrib.contenttypes",
    "django.contrib.sessions",
    "django.contrib.messages",
    "django.contrib.staticfiles",
    "tasks",
]

MIDDLEWARE = [
    "django.middleware.security.SecurityMiddleware",
    "django.contrib.sessions.middleware.SessionMiddleware",
    "django.middleware.common.CommonMiddleware",
    "django.middleware.csrf.CsrfViewMiddleware",
    "django.contrib.auth.middleware.AuthenticationMiddleware",
    "django.contrib.messages.middleware.MessageMiddleware",
    "django.middleware.clickjacking.XFrameOptionsMiddleware",
]

ROOT_URLCONF = "mysite.urls"

TEMPLATES = [
    {
        "BACKEND": "django.template.backends.django.DjangoTemplates",
        "DIRS": [],
        "APP_DIRS": True,
        "OPTIONS": {
            "context_processors": [
                "django.template.context_processors.request",
                "django.contrib.auth.context_processors.auth",
                "django.contrib.messages.context_processors.messages",
            ],
        },
    },
]

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.sqlite3",
        "NAME": BASE_DIR / "db.sqlite3",
    }
}

LANGUAGE_CODE = "en-us"
TIME_ZONE = "UTC"
USE_I18N = True
USE_TZ = True

STATIC_URL = "static/"