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Accessing environment variables with a magic module.

Project Description

Accessing environment variables with a magic module.

>>> import os
>>> from envcfg.raw.python import CONFIGURE_OPTS
'--enable-shared --enable-universalsdk=/ --with-universal-archs=intel'

It works with many frameworks such as Django and Flask. Then you can store your config in the environment variables instead of framework-specific config files. It is recommended by 12-Factor.


$ pip install python-envcfg

Supported Formats

  • import as config: Import each FOO_* environment variable as string.
  • import as config: Import each FOO_* environment variable as JSON body.
  • import as config: Try to import each FOO_* environment variable as JSON body, if fail then import it as string.

There is an example table:

Environment Variable Python Import Statement Python Variable Value
FOO_NAME=foo 'foo'
FOO_NAME="foo" '"foo"'
FOO_NUM1=42 '42'
FOO_NUM1="42" '"42"'
FOO_NAME=foo ImportError
FOO_NAME="foo" 'foo'
FOO_NUM1=42 42
FOO_NUM1="42" '42'
FOO_NAME=foo 'foo'
FOO_NAME="foo" 'foo'
FOO_NUM1=42 42
FOO_NUM1="42" '42'


Uses with Flask

  1. Defines environment variables with a prefix:

    $ cat .env  # should not checked into VCS
    # values are valid JSON expressions
  2. Creates Flask app and loads config from python-envcfg:

    $ cat
    app = Flask(__name__)
    app.config.from_object('envcfg.json.myapp')  # MYAPP_ -> .myapp
  3. Enters your app with those environment variables:

    $ env $(cat .env | xargs) python

Uses with Django

  1. Creates a django project and moves all sensitive config items into the environment variables:

    $ cat djapp/  # codebase-scope config
    $ cat .env  # environment-scope config, should not checked into VCS
    # values are valid JSON expressions
  2. Adds importing statements in the end of module:

    $ tail -n 2 djapp/
    # importing all config items stored in the environment variables
    from envcfg.json.djapp import *  # noqa
  3. Runs your Django app with environment variables:

    $ env $(cat .env | xargs) python runserver

Uses with Tornado

  1. Defines environment variables with a prefix:

    $ cat .env
    export TORAPP_PORT='8888'
    export TORAPP_MYSQL_HOST='""'
    export TORAPP_MYSQL_DATABASE='"database"'
  2. Creates a Tornado project and loads config:

    $ cat torapp/
    from tornado.web import Application, RequestHandler
    from tornado.ioloop import IOLoop
    from tornado.options import define, options
    from tordb import Connection
    def options_from_object(*args, **kwargs):
        module = __import__(*args, **kwargs)
        for name, value in vars(module).items():
            name = name.lower()
            if name in options._options:
    class IndexHandler(RequestHandler):
        def initialize(self):
            self.db = Connection(options.mysql_host, options.mysql_database)
        def get(self):
            pass  # some database operations with ``self.db``
    application = Application([
        (r'/', IndexHandler),
    define('port', type=int)
    define('mysql_host', type=unicode)
    define('mysql_database', type=unicode)
    options_from_object('envcfg.json.torapp', fromlist=['torapp'])
    if __name__ == '__main__':
  3. Runs your Tornado app:

    $ env $(cat .env | xargs) python

Works on Projects

In development, we can work with per-project environments but no more typing source foo/bar.

I recommend to put your project-specified environment variables in {PROJECT_ROOT}/.env and mark the .env as ignored in your VCS. For example, you can write /.env in .gitignore if you are using Git, and put a .env.example as a copying template for new-cloned projects.

And then, you can use some utility such as honcho or autoenv to apply the .env automatically.

For honcho:

$ echo 'MYPROJECT_DEBUG=true' >> .env
$ echo 'web: python runserver' >> Procfile
$ honcho run python check-debug
$ honcho start web
Starting development server at

For autoenv:

$ echo 'MYPROJECT_DEBUG=true' >> myproject/.env
$ cd myproject
$ python check-debug
$ python runserver
Starting development server at


If you want to report bugs or request features, please create issues on GitHub Issues.

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