byoc — Build Your Own Config

BYOC is a python library for integrating configuration values from any number/kind of sources, e.g. files, command-line arguments, environment variables, remote JSON APIs, etc. The primary goal of BYOC is to give you complete control over your configuration. This means:

  • Complete control over how files, options, etc. are named and organized.

  • Complete control over how values from different config sources are parsed and merged.

  • Support for any kind of file format, argument parsing library, etc.

  • No opinions about anything enforced by BYOC.

To use BYOC, you would create a class with special attributes (called parameters) that know where to look for configuration values. When these parameters are accessed, the desired values are looked up, possibly merged, possibly cached, and returned. Here’s a brief example:

import byoc
from byoc import Key, DocoptConfig, AppDirsConfig

class Greet(byoc.App):
    Say a greeting.

        greet <name> [-g <greeting>]

    # Define which config sources are available to this class.
    __config__ = [

    # Define how to search for each config value.
    name = byoc.param(
            Key(DocoptConfig, '<name>'),
    greeting = byoc.param(
            Key(DocoptConfig, '-g'),
            Key(AppDirsConfig, 'greeting'),

    def main(self):
        print(f"{self.greeting}, {}!")

if __name__ == '__main__':

We can configure this script from the command line:

$ ./greet 'Sir Bedevere'
Hello, Sir Bedevere!
$ ./greet 'Sir Lancelot' -g Goodbye
Goodbye, Sir Lancelot!

…or from its config files:

$ mkdir -p ~/.config/greet
$ echo "greeting: Run away" > ~/.config/greet/conf.yml
$ greet 'Sir Robin'
Run away, Sir Robin!

This example only scratches the surface, but hopefully you can already get a sense for how powerful and flexible these parameters are. For more information, refer to the following examples (in lieu of complete documentation).


For some examples of byoc being used in real scripts, check out the Stepwise — Molecular Biology repository. Almost every script in this repository uses byoc. Below are some particular scripts that might be useful:

Simple scripts:

Long but straight-forward scripts:

Complex scripts:


    This script features parameters that depend on other parameters. Specifically, the user must provide values for any three of volume, conc_high, conc_low, and factor. Whichever one isn’t specified is inferred from the ones that are. This is implemented by making the byoc parameters (which in this case read only from the command-line and not from any config files) private, then adding public properties that are calculated from the private ones.


    This script is actually pretty simple, but it makes used of __bareinit__() to download some data from the internet. As alluded to above, __init__() is not called when App instances are initialized from the command-line, because __init__() might require arbitrary arguments and is therefore considered to be part of the python API. Instead, App instances are initialized by calling __bareinit__() with no arguments.


    This script defines a custom Config class to read from a sequence database. (This example might go out of date, though; I have plans to move that custom Config into a different package.)