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Configuration library for Python applications

Project description

Everett is a configuration library.

License:MPL v2


This library tries to do configuration with minimal “fanciness”:

Configuration with Everett:

  • is composeable and flexible
  • makes it easier to provide helpful error messages for users trying to configure your software
  • can pull configuration from a variety of specified sources (environment, ini files, dict, write-your-own)
  • supports parsing values (bool, int, lists, …, write-your-own)
  • supports key namespaces
  • facilitates writing tests that change configuration values
  • supports component architectures with auto-documentation of configuration with a Sphinx autocomponent directive

Everett is inspired by python-decouple and configman.

Why not other libs?

Most other libraries I looked at had one or more of the following issues:

  • were tied to a specific web app framework
  • didn’t allow you to specify configuration sources
  • provided poor error messages when you configure things wrong
  • had a global configuration object
  • made it really hard to override specific configuration when writing tests
  • had no facilities for auto-documenting configuration for components

Quick start

Say you’re writing a web app using some framework that doesn’t provide infrastructure for configuration.

You want to pull configuration from an INI file stored in a place specified by FOO_INI in the environment. You want to pull infrastructure values from the environment. Values from the environment should override values from the INI file.

First, you set up your ConfigManager in your webapp:

from everett.manager import ConfigManager, ConfigOSEnv, ConfigIniEnv

class MyWSGIApp(SomeFrameworkApp):
    def __init__(self):
        self.config = ConfigManager(
            # Specify one or more configuration environments in
            # the order they should be checked
                # Looks in OS environment first

                # Looks in INI files in order specified

            # Make it easy for users to find your configuration
            # docs
            doc='Check for docs'

        # Set ``is_debug`` based on configuration
        self.is_debug = self.config('debug', parser=bool)

def get_app():
    return MyWSGIApp()

Now all configuration for the app can be pulled from the .config property.

Let’s write some tests that verify behavior based on the debug configuration value:

from everett.manager import config_override

def test_debug_true():
    app = get_app()

def test_debug_false():
    app = get_app()

This works with frameworks that do have configuration infrastructure like Django and Flask.

This works with non-web things, too, like command line programs.

Everett supports components, too. Say your app needs to connect to RabbitMQ. With Everett, you can wrap the configuration up with the component:

from everett.component import RequiredConfigMixin, ConfigOptions

class RabbitMQComponent(RequiredConfigMixin):
    required_config = ConfigOptions()
        doc='RabbitMQ host to connect to'
        doc='Port to use',
        doc='Queue to insert things into'

    def __init__(self, config):
        # Bind the configuration to just the configuration this
        # component requires such that this component is
        # self-contained.
        self.config = config.with_options(self) = self.config('host')
        self.port = self.config('port')
        self.queue_name = self.config('queue_name')

Then instantiate a RabbitMQComponent, but with configuration in the rmq namespace:

queue = RabbitMQComponent(config.with_namespace('rmq'))

In your environment, you would provide RMQ_HOST, etc for this component.

You can auto-document the configuration for this component in your Sphinx docs with:

.. autocomponent::

Say your app actually needs to connect to two separate queues–one for regular processing and one for priority processing:

regular_queue = RabbitMQComponent(
priority_queue = RabbitMQComponent(

In your environment, you provide the regular queue configuration with RMQ_REGULAR_HOST, etc and the priority queue configuration with RMQ_PRIORITY_HOST, etc.

Same component code. Two different instances pulling configuration from two different namespaces.

Components support subclassing, mixins and all that, too.


Install from PyPI


$ pip install everett

For hacking


# Clone the repository
$ git clone

# Create a virtualenvironment

# Install Everett and dev requirements
$ pip install -r requirements-dev.txt


0.9 (April 7th, 2017)


  • Rewrite Sphinx extension. The extension is now in the everett.sphinxext module and the directive is now .. autocomponent::. It generates better documentation and it now indexes Everett components and options.

    This is backwards-incompatible. You will need to update your Sphinx configuration and documentation.

  • Changed the HISTORY.rst structure.

  • Changed the repr for everett.NO_VALUE to "NO_VALUE".

  • InvalidValueError and ConfigurationMissingError now have namespace, key, and parser attributes allowing you to build your own messages.


  • Fix an example in the docs where the final key was backwards. Thank you, pjz!

Documentation fixes and updates.

0.8 (January 24th, 2017)


  • Add :namespace: and :case: arguments to autoconfig directive. These make it easier to cater your documentation to your project’s needs.
  • Add support for Python 3.6.

Minor documentation fixes and updates.

0.7 (January 5th, 2017)


  • Feature: You can now include documentation hints and urls for ConfigManager objects and config options. This will make it easier for your users to debug configuration errors they’re having with your software.


  • Fix ListOf so it returns empty lists rather than a list with a single empty string.

Documentation fixes and updates.

0.6 (November 28th, 2016)


  • Add RequiredConfigMixin.get_runtime_config() which returns the runtime configuration for a component or tree of components. This lets you print runtime configuration at startup, generate INI files, etc.
  • Add ConfigObjEnv which lets you use an object for configuration. This works with argparse’s Namespace amongst other things.


  • Change :show-docstring: to take an optional value which is the attribute to pull docstring content from. This means you don’t have to mix programming documentation with user documentation–they can be in different attributes.
  • Improve configuration-related exceptions. With Python 3, configuration errors all derive from ConfigurationError and have helpful error messages that should make it clear what’s wrong with the configuration value. With Python 2, you can get other kinds of Exceptions thrown depending on the parser used, but configuration error messages should still be helpful.

Documentation fixes and updates.

0.5 (November 8th, 2016)


  • Add :show-docstring: flag to autoconfig directive.
  • Add :hide-classname: flag to autoconfig directive.


  • Rewrite ConfigIniEnv to use configobj which allows for nested sections in INI files. This also allows you to specify multiple INI files and have later ones override earlier ones.


  • Fix autoconfig Sphinx directive and add tests–it was all kinds of broken.

Documentation fixes and updates.

0.4 (October 27th, 2016)


  • Add raw_value argument to config calls. This makes it easier to write code that prints configuration.


  • Fix listify(None) to return [].

Documentation fixes and updates.

0.3.1 (October 12th, 2016)


  • Fix alternate_keys with components. Previously it worked for everything but components. Now it works with components, too.

Documentation fixes and updates.

0.3 (October 6th, 2016)


  • Add ConfigManager.from_dict() shorthand for building configuration instances.
  • Add .get_namespace() to ConfigManager and friends for getting the complete namespace for a given config instance as a list of strings.
  • Add alternate_keys to config call. This lets you specify a list of keys in order to try if the primary key doesn’t find a value. This is helpful for deprecating keys that you used to use in a backwards-compatible way.
  • Add root: prefix to keys allowing you to look outside of the current namespace and at the configuration root for configuration values.


  • Make ConfigDictEnv case-insensitive to keys and namespaces.

Documentation fixes and updates.

0.2 (August 16th, 2016)


  • Add ConfigEnvFileEnv for supporting .env files. Thank you, Paul!
  • Add “on” and “off” as valid boolean values. This makes it easier to use config for feature flippers. Thank you, Paul!


  • Change ConfigIniEnv to take a single path or list of paths. Thank you, Paul!
  • Make NO_VALUE falsy.


  • Fix __call__ returning None–it should return NO_VALUE.

Lots of docs updates: finished the section about making your own parsers, added a section on using dj-database-url, added a section on django-cache-url and expanded on existing examples.

0.1 (August 1st, 2016)

Initial writing.

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