How to log/display app name, host and port upon startup?

In my simple Flask app, I've created the following .flaskenv file:

FLASK_APP=simpleflask.app
FLASK_RUN_HOST=127.0.0.1
FLASK_RUN_PORT=60210

Now, I would like my app to log the following message upon startup:

Running my.flask.app on http://127.0.0.1:60210 ...

The message should be logged just once, not per each request.

Preferably, I would like to avoid parsing .flaskenv on my own, but rather use some internal Flask objects and obtain this information dynamically.

Any idea how to achieve this?

Answer

You can use os.environ.get('<VAR_NAME>') to get values of envvars imported by flask run command from .flaskenv file at runtime.

You can print info you want with the following block before the app.run is executed:

flaskApp = os.environ.get('FLASK_APP')
flaskRunHost = os.environ.get('FLASK_RUN_HOST')
flaskRunPort = os.environ.get('FLASK_RUN_PORT')

print(f"Running {flaskApp} on http://{flaskRunHost}:{flaskRunPort} ...")

(replace print with preferred logging method)