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Override Flask configuration via Cookie at runtime.

Project description


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This extension allows to change the configuration of a Flask application at runtime. This behavior is controlled by cookie and therefore is contained to the session of an unique user; configuration changes are not affecting other users.

A common usage is to quickly change options in staging environment without having to redeploy configuration changes. For example, we use it for an external API location or a feature switch like using minified Javascript files or not.

The configuration options able to be overridden are limited and configurable as well (using CONFIG_OVERRIDE_EXTENDABLE_VARS). This option can NOT be overridden for security reason.

The idea is to replace the configuration object of a Flask application by a proxy object, whom behavior can be controlled/changed upon request while exposing the same interface as a Flask configuration. The extension also provide a blueprint (default base url to /config_override/) to control the cookie via some simple HTTP calls; this is automatically attached to the application.


Via Pypi:

pip install flask-config-override


Once installed, first attach the extension to your Flask application:

from flask import Flask from flask.ext.config_override import ConfigOverride

app = Flask(__name__) app.config[‘FOO’] = ‘bar’

# Enable the override for the DEBUG option (default to false) app.config[‘CONFIG_OVERRIDE_EXTENDABLE_VARS’] = [‘FOO’] config_override = ConfigOverride(app)

# configure your routes and what not…

Launch your app, then open your browser and go to this url to setup the FOO option to another value; here “toto”:


Your session will now run with the settings FOO set to the new value. You can access it normally from app.config[‘FOO’] within the context of a request.

To see the current changes, you can visit this url:


And to remove the changes, you just need to clear your cookie or go there:



  • First install nose for test discovery: pip install nose
  • Then run the tests within a virtual environment: nosetests


Feel free to post issues, pull requests in github or contact me directly on twitter @el_boby.

Immediate TODOs

  • test for cookie_utils
  • test for proxy_config (based on flask one)
  • documentation API (sphinx)


  • Override by Environment variables.
  • Flask Debug Toolbar integration.

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