Log application loaded event

Hi,

I’d like to log to a database that user has started my application. What’s the best way?

I thought to put it inside function that creates app.layout, but that triggers:

Attempting to assign a callback to the application but
the `layout` property has not been assigned.
Assign the `layout` property before assigning callbacks.
Alternatively, suppress this warning by setting
`app.config['suppress_callback_exceptions']=True`

I could do that, but prefer not to. I like these exceptions :).