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:

http://antenna.readthedocs.io/en/latest/configuration.html#application

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

http://antenna.readthedocs.io/en/latest/genindex.html

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.

Enjoy!

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