Everett is a Python configuration library for your app.
| Code: | https://github.com/willkg/everett |
|---|---|
| Issues: | https://github.com/willkg/everett/issues |
| License: | MPL v2 |
| Documentation: | https://everett.readthedocs.io/ |
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
- supports auto-documentation of configuration with a Sphinx
autocomponentdirective - 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.
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 users configure things wrong
- had a global configuration object
- made it really hard to override specific configuration when writing tests
- had no facilities for auto-generating configuration documentation
You have an app and want it to look for configuration in an .env file then
the environment. You can do this:
from everett.manager import ConfigManager config = ConfigManager.basic_config()
Then you can use it like this:
debug_mode = config('debug', parser=bool)
When you outgrow that or need different variations of it, you can change
that to creating a ConfigManager from scratch.
We have an app and want to pull configuration from an INI file stored in
a place specified by MYAPP_INI in the environment, ~/.myapp.ini,
or /etc/myapp.ini in that order.
We want to pull infrastructure values from the environment.
Values from the environment should override values from the INI file.
First, we set up our ConfigManager:
import os
import sys
from everett.manager import ConfigManager, ConfigOSEnv, ConfigIniEnv
def get_config():
return 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.'
)
Then we use it:
def is_debug(config):
return config('debug', parser=bool,
doc='Switch debug mode on and off.')
def main(args):
config = get_config()
if is_debug(config):
print('DEBUG MODE ON!')
if __name__ == '__main__':
sys.exit(main(sys.argv[1:]))
Let's write some tests that verify behavior based on the debug
configuration value:
from myapp import get_config, is_debug
from everett.manager import config_override
@config_override(DEBUG='true')
def test_debug_true():
assert is_debug(get_config()) is True
@config_override(DEBUG='false')
def test_debug_false():
assert is_debug(get_config()) is False
If the user sets DEBUG wrong, they get a helpful error message with
the documentation for the configuration option and the ConfigManager:
$ DEBUG=foo python myprogram.py <traceback> namespace=None key=debug requires a value parseable by bool Switch debug mode on and off. Check https://example.com/configuration for docs.
Everett works with frameworks that have configuration infrastructure like Django and Flask.
Everett works with non-web things like scripts and servers and other things.
Everett supports components. 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-generate configuration documentation for this component in your
Sphinx docs by including the everett.sphinxext Sphinx extension and
using the autocomponent directive:
.. autocomponent:: 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.
Run:
$ pip install everett
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