Everett v0.9 released and why you should use Everett

What is it?

Everett is a Python configuration library.

Configuration with Everett:

  • is composeable and flexible

  • makes it easier to provide helpful error messages for users trying to configure your software

  • supports auto-documentation of configuration with a Sphinx autocomponent directive

  • supports easy testing with configuration override

  • can pull configuration from a variety of specified sources (environment, ini files, dict, write-your-own)

  • supports parsing values (bool, int, lists of things, classes, write-your-own)

  • supports key namespaces

  • supports component architectures

  • works with whatever you're writing--command line tools, web sites, system daemons, etc

Everett is inspired by python-decouple and configman.

v0.9 released!

This release focused on overhauling the Sphinx extension. It now:

  • has an Everett domain

  • supports roles

  • indexes Everett components and options

  • looks a lot better

This was the last big thing I wanted to do before doing a 1.0 release. I consider Everett 0.9 to be a solid beta. Next release will be a 1.0.

Why you should take a look at Everett

At Mozilla, I'm using Everett 0.9 for Antenna which is running in our -stage environment and will go to -prod very soon. Antenna is the edge of the crash ingestion pipeline for Mozilla Firefox.

When writing Antenna, I started out with python-decouple, but I didn't like the way python-decouple dealt with configuration errors (it's pretty hands-off) and I really wanted to automatically generate documentation from my configuration code. Why write the same stuff twice especially where it's a critical part of setting Antenna up and the part everyone will trip over first?

Here's the configuration documentation for Antenna:


Here's the index which makes it easy to find things by component or by option (in this case, environment variables):


When you configure Antenna incorrectly, it spits out an error message like this:

1  <traceback omitted, but it'd be here>
2  everett.InvalidValueError: ValueError: invalid literal for int() with base 10: 'foo'
3  namespace=None key=statsd_port requires a value parseable by int
4  Port for the statsd server
5  For configuration help, see https://antenna.readthedocs.io/en/latest/configuration.html

So what's here?:

  • Block 1 is the traceback so you can trace the code if you need to.

  • Line 2 is the exception type and message

  • Line 3 tells you the namespace, key, and parser used

  • Line 4 is the documentation for that specific configuration option

  • Line 5 is the "see also" documentation for the component with that configuration option

Is it beautiful? No. 1 But it gives you enough information to know what the problem is and where to go for more information.

Further, in Python 3, Everett will always raise a subclass of ConfigurationError so if you don't like the output, you can tailor it to your project's needs. 2

First-class docs. First-class configuration error help. First-class testing. This is why I created Everett.

If this sounds useful to you, take it for a spin. It's almost a drop-in replacement for python-decouple 3 and os.environ.get('CONFIGVAR', 'default_value') style of configuration.



I would love some help here--making that information easier to parse would be great for a 1.0 release.


Python 2 doesn't support exception chaining and I didn't want to stomp on the original exception thrown, so in Python 2, Everett doesn't wrap exceptions.


python-decouple is a great project and does a good job at what it was built to do. I don't mean to demean it in any way. I have additional requirements that python-decouple doesn't do well and that's where I'm coming from.

Where to go for more

For more specifics on this release, see here: http://everett.readthedocs.io/en/latest/history.html#april-7th-2017

Documentation and quickstart here: https://everett.readthedocs.org/en/v0.9/

Source code and issue tracker here: https://github.com/willkg/everett

Want to comment? Send an email to willkg at bluesock dot org. Include the url for the blog entry in your comment so I have some context as to what you're talking about.