Python Decouple 2.2: Strict separation of settings from code

Decouple helps you to organize your settings so that you can change parameters without having to redeploy your app.

It also makes easy for you to:

  1. store parameters on ini or .env files;
  2. define comprehensive default values;
  3. properly convert values to the correct data type;
  4. have only one configuration module to rule all your instances.

It was originally designed for Django, but became an independent generic tool for separating settings from code.

Test Status
Code Helth
Latest PyPI version
Number of PyPI downloads

Why?

Web framework’s settings stores many different kinds of parameters:

  • Locale and i18n;
  • Middlewares and Installed Apps;
  • Resource handles to the database, Memcached, and other backing services;
  • Credentials to external services such as Amazon S3 or Twitter;
  • Per-deploy values such as the canonical hostname for the instance.

The first 2 are project settings the last 3 are instance settings.

You should be able to change instance settings without redeploying your app.

Why not just use environment variables?

Envvars works, but since os.environ only returns strings, it’s tricky.

Let’s say you have an envvar DEBUG=False. If you run:

It will print True, because os.environ['DEBUG'] returns the string "False". Since it’s a non-empty string, it will be evaluated as True.

Decouple provides a solution that doesn’t look like a workaround: config('DEBUG', cast=bool).

Install

Usage

On your settings.py.

  1. Import the config object:
  2. Retrieve the configuration parameters:

Where the settings data are stored?

Decouple supports both .ini and .env files.

Ini file

Simply create a settings.ini next to your configuration module in the form:

Note: Since ConfigParser supports string interpolation, to represent the character % you need to escape it as %%.

Env file

Simply create a .env text file on your repository’s root directory in the form:

Example: How do I use it with Django?

Given that I have a .env file at my repository root directory, here is a snippet of my settings.py.

I also recommend using unipath and dj-datatabase-url.

Atention with undefined parameters

On the above example, all configuration parameters except SECRET_KEY = config('SECRET_KEY') have a default value to fallback if it does not exist on the .env file.

If SECRET_KEY is not present on the .env, decouple will raise an UndefinedValueError.

This fail fast policy helps you avoid chasing misbehaviors when you eventually forget a parameter.

How it works?

Decouple is made of 5 classes:

  • Config

    Coordinates all the configuration retrieval.

  • RepositoryIni

    Can read values from ini files.

  • RepositoryEnv

    Can read .env files and when a parameter does not exist there,
    it tries to find it on os.environ.

    This process does not change nor add any environment variables.

  • RepositoryShell

    Can only read values from os.environ.

  • AutoConfig

    Detects which configuration repository you’re using.

    It recursively searches up your configuration module path looking for a
    settings.ini or a .env file.

The config object is an instance of AutoConfig to improve decouple‘s usage.

License

The MIT License (MIT)

Copyright (c) 2013 Henrique Bastos <henrique at bastos dot net>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

  • Tadek Teleżyński

    Great module! I am using it in all of my Django projects.
    Just opened an issue on GH repo with potential extension and started wondering if you still develop this module or has it become frozen?

  • Thanks! This is really awesome and I’m using it on one of my projects. However, you say “it helps you to organize my settings so that you can change parameters without having to redeploy your app” but every time I change parameters, I have to restart my webserver. This is considered a redeploy, right?

    Thanks!

    • Thiago, no. Redeploy involve sending a code to the server, installing dependencies, building the app. Restarting the app is an atomic and simple operation. Since settings are loaded when the process starts, restarting is just a restriction.