Python application configuration
Python application configuration
What is Bison?
Bison is a configuration solution for Python applications that aims to be simple and intuitive. It supports:
- reading from YAML config files
- reading from environment variables
- setting explicit values
- setting defaults
- configuration validation
- configuration access/manipulation with dot notation
Instead of implementing custom configuration reading and parsing, you can use Bison to handle it for you.
Bison uses the following precedence order. Each item in the list takes precedence over the item below it.
- override (e.g. calling
- config file
Bison can be installed with
pip install bison
pipenv install bison
Creating a configuration Scheme
A configuration scheme is not required by Bison, but having one allows you to set default values for configuration fields as well as do configuration validation. It is pretty easy to create a new Scheme:
scheme = bison.Scheme()
A Scheme is really just a container for configuration options, so without any options, a Scheme is somewhat useless.
There are currently three types of configuration options:
Their intended functionality should be mostly obvious from their names. An
a singular value in a configuration. A
DictOption represents a dictionary or mapping of values
in a configuration. A
ListOption represents a list of values in a configuration.
See the documentation for more on how options can be configured.
Any number of options can be added to a Scheme, but as a simple example we can define a Scheme which expects a key "log", and a key "count".
scheme = bison.Scheme( bison.Option('log'), bison.Option('count'), )
Validation operates based on the constraints set on the options. Above, there are no constraints (other than the need for those keys to exist), so any value for "log" and "count" will pass validation.
An option can be constrained in different ways by using its keyword arguments. For example, to ensure the value for "count" is an integer,
Or, to restrict the values to a set of choices
bison.Option('log', choices=['debug', 'info', 'warn', 'error'])
The documentation goes into more detail about other validation settings.
If a default value is not set on an option, it is considered required. In these cases, if the key specified by that value is not present in the parse configuration, it will cause a validation failure.
If a default value is set, then the absence of that field in the configuration will not cause a validation failure.
Once you have a Scheme to use (if you'd like to), it will need to be passed to a Bison object to manage the config building.
scheme = bison.Scheme() config = bison.Bison(scheme)
There are a few options that can be set on the Bison object to change how it searches for and builds the unified configuration.
For reading configuration files
config.config_name = 'config' # name of the config file (no extension) config.add_config_paths( # paths to look in for the config file '.', '/tmp/app' ) config.config_format = bison.YAML # the config format to use
For reading environment variables
config.env_prefix = "MY_APP" # the prefix to use for environment variables config.auto_env = True # automatically bind all options to env variables based on their key
Building the unified config
Once the scheme has been set (if using) and Bison has been configured, the only thing left to do is to read in all the config sources and parse them into a unified config. This is done simply with
Below is a complete example for parsing a hypothetical application configuration which is described by the following YAML config.
log: debug port: 5000 settings: requests: timeout: 3 backends: - host: 10.1.2.3 port: 5001 - host: 10.1.2.4 port: 5013 - host: 10.1.2.5 port: 5044
import bison # the scheme for the configuration. this allows us to set defaults # and validate configuration data config_scheme = bison.Scheme( bison.Option('log', default='info', choices=['debug', 'info', 'warn', 'error']), bison.Option('port', field_type=int), bison.DictOption('settings', scheme=bison.Scheme( bison.DictOption('requests', scheme=bison.Scheme( bison.Option('timeout', field_type=int) )) )), bison.ListOption('backends', member_scheme=bison.Scheme( bison.Option('host', field_type=str), bison.Option('port', field_type=int) )) ) # create a new Bison instance to store and manage configuration data config = bison.Bison(scheme=config_scheme) # set the config file name to 'app' (default is 'config') and set the # search paths to '.' and '/tmp/app/config' config.config_name = 'app' config.add_config_paths('.', '/tmp/app/config') # set the environment variable prefix and enable auto-env config.env_prefix = 'MY_APP' config.auto_env = True # finally, parse the config sources to build the unified configuration config.parse()
See the example directory for this example along with demonstrations of how to access configuration data.
There is more that can be done to improve Bison and expand its functionality. If you wish to contribute, open a pull request. If you have questions or feature requests, open an issue. Below are some high level ideas for future improvements:
- Support additional configuration formats (JSON, TOML, ...)
- Versioned configurations
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