ImportError when trying to start flask app, but no stack trace printed

[haimat]

I am trying to set up a flask application on my new machine. First I checked out the sources from our server - I am pretty sure the application directory structure is correct, as we are using it exactly like this on other machines.

However, when I try to run the app on my new computer I get the following error:

$ FLASK_ENV="development" FLASK_APP="run.py" flask run
 * Serving Flask app 'run.py' (lazy loading)
 * Environment: development
 * Debug mode: on
Usage: flask run [OPTIONS]
Try 'flask run --help' for help.

Error: While importing 'run', an ImportError was raised.

Problem is: No more output is printed, in particular no stack trace. So I don't know what exactly the problem is. How can I tell flask to print the stack trace?

Environment:

• Python version: 3.8.10
• Flask version: 2.0.2

[davidism]

Duplicate of #4307