configurenv

Utilities for simplifying application configuration

Description

This package provides two functions: envsubst and load_config_from_file.

envsubst was created to allow runtime substitution of environment variables into otherwise static configuration files.

load_config_from_file was created to extend Flask app configuration by reading configuration values from files specified by keys of the shape {NAME}_FILE. After passing those configuration values though envsubst (using the existing configuration as the context environment), it updates the {NAME} key of the original configuration.

Dependencies

• Python 3.10+
• PyYAML

Installation

pip install configurenv

Usage

envsubst

With this environment:

SERVER_NAME=test.example.com

Running this Python code:

from configurenv import envsubst

url = envsubst('http://${SERVER_NAME}/endpoint')

Results in url having the value 'http://test.example.com/endpoint'.

load_config_from_file

Typical usage is in the setup phase of a Flask app, after loading the initial config from somewhere else (often from environment variables).

With this environment:

MYAPP_USERNAME=jdoe
MYAPP_COLORMAP_FILE=colors.yml

And this colors.yml file:

danger: red
warning: yellow
alert: orange
info: blue

Running this Python code:

from flask import Flask
from configurenv import load_config_from_files

app = Flask(__name__)
app.config.from_prefixed_env('MYAPP')

load_config_from_files(app.config)

Will result in app.config containing these keys and values:

{
    'USERNAME': 'jdoe',
    'COLORMAP_FILE': 'colors.yml',
    'COLORMAP': {
        'danger': 'red',
        'warning': 'yellow',
        'alert': 'orange',
        'info': 'blue',
    },
}

The colors.yml could also refer to other configuration values.

With this environment:

MYAPP_USERNAME=jdoe
MYAPP_DANGER_COLOR=hotpink
MYAPP_COLORMAP_FILE=colors.yml

And this colors.yml file:

danger: ${DANGER_COLOR}
warning: yellow
alert: orange
info: blue

Running the same Python code as above will result in app.config containing these keys and values:

{
    'USERNAME': 'jdoe',
    'DANGER_COLOR': 'hotpink',
    'COLORMAP_FILE': 'colors.yml',
    'COLORMAP': {
        'danger': 'hotpink',
        'warning': 'yellow',
        'alert': 'orange',
        'info': 'blue',
    },
}

Development Setup

git clone git@github.com:umd-lib/configurenv.git
cd configurenv
pyenv install $(cat .python-version) --skip-existing
python -m venv .venv --prompt "$(basename $PWD)-py$(cat .python-version)"
source .venv/bin/activate
pip install -e .[test]

Testing

Using pytest:

pytest

With test coverage information:

pytest --cov-report=term-missing --cov src

Code Style

Using ruff:

ruff check

History

envsubst originated in the Plastron project of the UMD Libraries; see also plastron.utils.envsubst

load_config_from_files originated in Solrizer project of the UMD Libraries; see also solrizer.web.load_config_from_files