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Configures Flask applications in a canonical way. Also auto-configures Heroku. Aims to standardize configuration.

Project description

Allows you to configure an application using pre-set methods.

from flask_appconfig import AppConfig

def create_app(configfile=None):
    app = Flask('myapp')
    AppConfig(app, configfile)
    return app

The application returned by create_app will, in order:

  1. Load default settings from a module called myapp.default_config, if it exists. (method described in )

  2. Load settings from a configuration file whose name is given in the environment variable MYAPP_CONFIG (see link from 1.).

  3. Load json or string values directly from environment variables that start with a prefix of MYAPP_, i.e. setting MYAPP_SQLALCHEMY_ECHO=true will cause the setting of SQLALCHEMY_ECHO to be True.

Any of these behaviors can be altered or disabled by passing the appropriate options to the constructor or init_app().

Heroku support

Flask-AppConfig supports configuring a number of services through HerokuConfig:

from flask_appconfig import HerokuConfig

def create_app(configfile=None):
    app = Flask('myapp')
    HerokuConfig(app, configfile)
    return app

Works like the example above, but environment variables set by various Heroku addons will be parsed as json and converted to configuration variables accordingly. Forexample, when enabling Mailgun, the configuration of Flask-Mail will be automatically be set correctly.

Using “ENV-only”

If you only want to use the environment-parsing functions of Flask-AppConfig, the appropriate functions are exposed:

from flask_appconfig.heroku import from_heroku_envvars
from flask_appconfig.env import from_envvars

# from environment variables. note that you need to set the prefix, as
# no auto-detection can be done without an app object
from_envvars(app.config, + '_')

# also possible: parse heroku configuration values
# any dict-like object will do as the first parameter


Via PyPI:

$ pip install flask-appconfig

Requires Python 2.7.

flask utility

If you want to get started quickly without thinking a lot about writing a run script, the flask utility supports the create_app/factory pattern:

$ flask --app=myapp dev

This will import a module myapp, and call

Other options can come in handy as well:

$ flask --app=myapp dev -S -p 8000

Runs the app on port 8080, with SSL enabled. You can also set the FLASK_APP environment variable or set FLASK_APP inside .env and omit the --app parameter.

Note that the flask utility is subject to change, as it will conflict with the CLI functionality of Flask 1.0. The API is currently kept close, but it will see changes once Flask 1.0 is released.

Flask-Debug and Flask-DebugToolbar support

flask automatically activates Flask-Debug and Flask-DebugToolbar on your application; this allows to have it installed locally while not having to install any debug code in production. You can suppress this behavior with the -E/--no-flask-debug flag.

Note that these features are only enabled if you install either of these extensions manually; they are not dependencies of Flask-Appconfig.

Thoughts on Configuration

There is a lot of ways to configure a Flask application and often times, less-than-optimal ones are chosen in a hurry.

This extension aims to do three things:

  1. Set a “standard” of doing configuration that is flexible and in-line with the official docs and (what I consider) good practices.

  2. Make it as convenient as possible to provide these configuration methods in an application.

  3. Auto-configure on Heroku as much as possible without sacrificing 1. and 2. seems to capture a good amount of good thoughts on the issue and Flask-Appconfig should aid you in writing an application that follows the principles laid out there.

Providing defaults

Defaults should be included and overridable, without altering the file containing the defaults.

Separate code and configuration

It should be possible to install the app to a read-only (possibly system-wide) location, without having to store configuration files (or, even worse, configuration modules) inside its folders.

Environment variables and instance folders make this possible. As an added benefit, configuration does not need to be stored alongside the code in version control.

No code necessary for most deployments using the factory-method pattern

When deploying with gunicorn, passing myapp:create_app() suffices to create an app instance, no boilerplate code to create the WSGI app should be necessary.

Multiple instances

Running multiple apps inside the same interpreter should also be possible. While this is slightly more complicated and may occasionally violate the “no-code” guideline above, it’s still straightforward by using configuration file parameters.


Flask-AppConfig is under “conceptional development”. The API or semantics may change in the future.

Send pull requests for more Heroku-apps to be supported. Send feedback via mail.


Backwards-incompatible changes, as they were introduced:


  • The flaskdev tool has been replaced with flask.

  • Using the new flask tool auto-reloading will also change by default. If a syntax error is introduced to the code, the app will try to restart after two seconds by default, instead of crashing. This can be suppressed with the ‘–extended-reload 0’ flag.

  • If the app import fails, flask will add . to sys.path and try to to import once again.

  • Experimental commands serve and db have been added.


  • Environment variables are no longer prefixed with FLASK_ by default, but rather use APPNAME_ (with APPNAME being the applications name in uppercase).

  • MYAPP_SETTINGS became MYAPP_CONFIG, default_settings became default_config.

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