DecoupleR

Strict separation of settings from code.

DecoupleR is an attempt to port the excellent python-decouple library into R.

As stated by its original author, python-decouple makes it easy to:

• store parameters in ini or .env files;
• define comprehensive default values;
• properly convert values to the correct data type;
• have only one configuration module to rule all your instances.

DecoupleR general behavior have been in order to mimic as much as possible python-decouple, and is tested against python-decouple unit tests.

Priority rules and config files serach

DecoupleR always searches for Options in this order:

1. Environment variables;
2. Repository: ini or .env file;
3. Default argument passed to config.

It has to be noted that environment variables have precedence over config files in order to be unix consistent.

Config file search

The config files are searched for, by default, in the working directory, or in the any other directory provided via the path argument. If no config files, settings.ini or .env is found in the directory, the search will continue in its parent directories.

Example

On-the-fly parameter evaluation

Parameter value can be retrieve anytime by invoking the DecoupleR::get_var function. If the config parameter is not provided, a config file search will be carried out at each function call.

  get_var('R_HOME')

Preload the config file

In order to avoid recurrent config file search at each get_var call, the config file search can be carried out once via the get_config function. A list will be returned, containing the parameters from the config file if any.

Implementated parser

DecoupleR supports both .ini and .env files.

Ini file

DecoupleR can read ini files and provide simple interpolation.

Simply create a `settings.ini in your working directory or in its roots.

  [settings]
  DEBUG=True
  TEMPLATE_DEBUG=%(DEBUG)s
  SECRET_KEY=ARANDOMSECRETKEY
  DATABASE_URL=mysql://myuser:mypassword@myhost/mydatabase
  PERCENTILE=90%%
  #COMMENTED=42

Env file

Simply create a .env text file on your repository’s root directory in the form:

    DEBUG=True
    TEMPLATE_DEBUG=True
    SECRET_KEY=ARANDOMSECRETKEY
    DATABASE_URL=mysql://myuser:mypassword@myhost/mydatabase
    PERCENTILE=90%
    #COMMENTED=42

undefined parameters

On the above example, all configuration parameters except SECRET_KEY = config('SECRET_KEY') have a default value to fallback if it does not exist on the .env file.

If SECRET_KEY is not present in the .env, DecoupleR will raise an error.

This fail fast policy helps you avoid chasing misbehaviors when you eventually forget a parameter.

Casting argument

By default, all values returned by DecoupleR are strings.

To easily specify a returned type, the get_var function accepts a cast argument which receives any callable, that will be used to transform the string value into something else. Some prefedined transformation have also been implementated:

• Integer: int, integer
• Bolean: bool, boolean, logical
• Float: float