Plotly Dash: Use SMTP logging handler when debug is false

Question

In Plotly Dash, I am trying to

1. determine if I am running in debug mode, and
2. change the logging handler to an SMTPHandler, only when the app is not running in Debug mode

What I tried:

import dash

app = dash.Dash(__name__)

if app.server.debug is False:
    print("Not in Debug mode")
    # app.logger.addHandler(mail_handler)

if __name__ == '__main__':
    app.run_server(debug=True, use_reloader=True)
    print(f"app.server.debug is {app.server.debug}")  # This code only executes after the server is shut down

I tried app.server.debug (and app.server.config["DEBUG"]) but both always return False. So I am not able to determine if the app is actually in debug mode or not.

This is my console output:

Not in Debug mode
Dash is running on http://127.0.0.1:8050/

 * Serving Flask app 'example_code' (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
Not in Debug mode

I assume this confusion is because the FLASK_DEBUG environment variable is not set, but even so, it does say * Debug mode: on so how to identify this during runtime?

And finally where do I add this debug mode check and change the handler - the debug is set in app.run_server() but adding any code immediately after that only executes after the server is shut down.

Answer 1

Maybe this approach will work for you? Just set a callback to run only once per program execution. (sorry for using globals, couldn't think of a cleaner way).

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State
import logging

app = dash.Dash(__name__)
app.layout = html.Div([dcc.Store(id='dummy_store')])
logger = logging.getLogger(__name__)
LOGGER_CONFIGURED = False


@app.callback(
    Output('dummy_store', 'data'),
    Input('dummy_store', 'data'),
)
def configure_logger(dummy_store):
    global LOGGER_CONFIGURED
    if LOGGER_CONFIGURED is False:
        print(f'configured logger with debug mode set to {app.server.debug}')
        # do something with the logger here
        LOGGER_CONFIGURED = True


if __name__ == '__main__':
    app.run_server(debug=True, use_reloader=True)