Auto reloading python Flask app upon code changes

In test/development environments

The werkzeug debugger already has an 'auto reload' function available that can be enabled by doing one of the following:

app.run(debug=True)

or

app.debug = True

You can also use a separate configuration file to manage all your setup if you need be. For example I use 'settings.py' with a 'DEBUG = True' option. Importing this file is easy too;

app.config.from_object('application.settings')

However this is not suitable for a production environment.

Production environment

Personally I chose Nginx + uWSGI over Apache + mod_wsgi for a few performance reasons but also the configuration options. The touch-reload option allows you to specify a file/folder that will cause the uWSGI application to reload your newly deployed flask app.

For example, your update script pulls your newest changes down and touches 'reload_me.txt' file. Your uWSGI ini script (which is kept up by Supervisord - obviously) has this line in it somewhere:

touch-reload = '/opt/virtual_environments/application/reload_me.txt'

I hope this helps!

Run the flask run CLI command with debug mode enabled, which will automatically enable the reloader. As of Flask 2.2, you can pass --app and --debug options on the command line.

$ flask --app main.py --debug run

--app can also be set to module:app or module:create_app instead of module.py. See the docs for a full explanation.

More options are available with:

$ flask run --help

Prior to Flask 2.2, you needed to set the FLASK_APP and FLASK_ENV=development environment variables.

$ export FLASK_APP=main.py
$ export FLASK_ENV=development
$ flask run

It is still possible to set FLASK_APP and FLASK_DEBUG=1 in Flask 2.2.

If you are talking about test/dev environments, then just use the debug option. It will auto-reload the flask app when a code change happens.

app.run(debug=True)

Or, from the shell:

$ export FLASK_DEBUG=1
$ flask run

http://flask.palletsprojects.com/quickstart/#debug-mode