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Load configuration variables from a file or environment

Project description

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Define configuration variables and load them from environment or JSON/YAML file. Also generates initial configuration files and documentation for your defined configuration.

Installation

pip install goodconf or pip install goodconf[yaml] if parsing/generating YAML files is required.

Usage

Examples:

# define a configuration
import base64
import os

from goodconf import GoodConf, Value

class MyConf(GoodConf):
    "Configuration for My App"
    DEBUG = Value(default=False, help="Toggle debugging.")
    DATABASE_URL = Value(
        default='postgres://localhost:5432/mydb',
        help="Database connection.")
    SECRET_KEY = Value(
        initial=lambda: base64.b64encode(os.urandom(60)).decode(),
        help="Used for cryptographic signing. "
        "https://docs.djangoproject.com/en/2.0/ref/settings/#secret-key")

config = MyConf()

# load a configuration
config.load('myapp.conf')

# access values as attributes on the GoodConf instance
config.DATABASE_URL

# generate an initial config file from the definition
print(MyConf.generate_yaml())

# generate documentation for a configuration
print(MyConf.generate_markdown())

GoodConf

Your subclassed GoodConf object can be initialized with the following keyword args:

  • file_env_var The name of an environment variable which can be used for the name of the configuration file to load.
  • default_files If no file is passed to the load method, try to load a configuration from these files in order.
  • load Trigger the load method during instanciation. Defaults to True.

Use plain-text docstring for use as a header when generating a configuration file.

Value

Declare configuration values by subclassing GoodConf and defining class attributes which are Value instances. They can be initialized with the following keyword args:

  • default Default value if none is provided. If left unset, loading
    a config that fails to provide this value will raise accept RequiredValueMissing exception.
  • initial Initial value to use when generating a config
  • cast_as Python type to cast variable as. Defaults to type of default (if provided) or str.
  • help Plain-text description of the value.

Django Usage

A helper is provided which monkey-patches Django’s management commands to accept a --config argument. Replace your manage.py with the following:

import sys
from goodconf.contrib.django import execute_from_command_line_with_config
# Define your GoodConf in `myproject/__init__.py`
from myproject import config

if __name__ == '__main__':
    execute_from_command_line_with_config(config, sys.argv)

Why?

I took inspiration from logan (used by Sentry) and derpconf (used by Thumbor). Both, however used Python files for configuration. I wanted a safer format and one that was easier to serialize data into from a configuration management system.

Environment Variables

I don’t like working with environment variables. First, there are potential security issues:

  1. Accidental leaks via logging or error reporting services.
  2. Child process inheritance (see ImageTragick for an idea why this could be bad).

Second, in practice on deployment environments, environment variables end up getting written to a number of files (cron, bash profile, service definitions, web server config, etc.). Not only is it cumbersome, but also increases the possibility of leaks via incorrect file permissions.

I prefer a single structured file which is explicitly read by the application. I also want it to be easy to run my applications on services like Heroku where environment variables are the preferred configuration method.

This module let’s me do things the way I prefer in environments I control, but still run them with environment variables on environments I don’t control with minimal fuss.

Project details


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