Encountered configuration_error when a Flask app was implemented with app.run(..., debug=False)

[rayluo]

There was a report stating that, a configuration_error (sometimes with an error trace) will be encountered when a Flask app.py containing with app.run(..., debug=False) at the end of app.py was started by python app.py.

[rayluo]

It turns out, a Flask app started that way does not automatically load environment variables from .env. I found only non-official article alluding to that (which was written one year after the original issue posted above). Nonetheless, nowadays, the recommended way to start a Flask application is flask run ... for example flask run -h localhost.