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Configuration library for Python applications

Project description

=======
Everett
=======

Everett is a configuration library.

:Code: https://github.com/willkg/everett
:Issues: https://github.com/willkg/everett/issues
:License: MPL v2
:Documentation: https://everett.readthedocs.io/


Goals
=====

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 ``autoconfig`` directive

Everett is inspired by `python-decouple
<https://github.com/henriquebastos/python-decouple>`_ and `configman
<https://configman.readthedocs.io/en/latest/>`_.


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
ConfigOSEnv(),

# Looks in INI files in order specified
ConfigIniEnv([
os.environ.get('MYAPP_INI'),
'~/.myapp.ini',
'/etc/myapp.ini'
]),
],

# Make it easy for users to find your configuration
# docs
doc='Check https://example.com/configuration 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

@config_override(DEBUG='true')
def test_debug_true():
app = get_app()
...

@config_override(DEBUG='false')
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()
required_config.add_option(
'host',
doc='RabbitMQ host to connect to'
)
required_config.add_option(
'port',
default='5672',
doc='Port to use',
parser=int
)
required_config.add_option(
'queue_name',
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.host = 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::

.. autoconfig:: path.to.RabbitMQComponent


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

regular_queue = RabbitMQComponent(
config.with_namespace('regular').with_namespace('rmq')
)
priority_queue = RabbitMQComponent(
config.with_namespace('priority').with_namespace('rmq')
)


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
---------

Run::

$ pip install everett


For hacking
-----------

Run::

# Clone the repository
$ git clone https://github.com/willkg/everett

# Create a virtualenvironment
...

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


History
=======

0.7 (January 5th, 2016)
-----------------------

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.

Bug: 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)
-------------------------

Feature: 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.

Feature: 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.

Feature: Add ``ConfigObjEnv`` which lets you use an object for configuration.
This works with argparse's Namespace amongst other things.

Feature: 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)
------------------------

Feature: Add ``:show-docstring:`` flag to ``autoconfig`` directive.

Feature: Add ``:hide-classname:`` flag to ``autoconfig`` directive.

Feature: 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.

Bug: Fix ``autoconfig`` Sphinx directive and add tests--it was all kinds of
broken.


0.4 (October 27th, 2016)
------------------------

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

Bug: Fix ``listify(None)`` to return ``[]``.

Documentation fixes and updates.


0.3.1 (October 12th, 2016)
--------------------------

Bug: Fix ``alternate_keys`` with components. Previously it worked for everything
but components. Now it works with components, too.


0.3 (October 6th, 2016)
-----------------------

Feature: Add ``ConfigManager.from_dict()`` shorthand for building configuration
instances.

Feature: Add ``.get_namespace()`` to ``ConfigManager`` and friends for getting
the complete namespace for a given config instance as a list of strings.

Feature: Make ``ConfigDictEnv`` case-insensitive to keys and namespaces.

Feature: 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.

Feature: Add ``root:`` prefix to keys allowing you to look outside of the
current namespace and at the configuration root for configuration values.


0.2 (August 16th, 2016)
-----------------------

Feature: Add ``ConfigEnvFileEnv`` for supporting ``.env`` files. Thank you,
Paul!

Feature: Change ``ConfigIniEnv`` to take a single path or list of paths. Thank
you, Paul!

Feature: Add "on" and "off" as valid boolean values. This makes it easier to use
config for feature flippers. Thank you, Paul!

Feature: Make ``NO_VALUE`` falsy.

Bug: 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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