Hi, is it possible to define an app callback without an output? Best

This is an old post, but it’s still popular, so I wanted to make sure anyone who finds it through a search gets the current answer. Callbacks with no outputs have been supported since Dash 2.17: Callbacks with No Outputs - Advanced Callbacks | Dash for Python Documentation |... In thi…

Callbacks now handle PreventUpdate() exception rising by ignoring the callback output. So the callback can have output set to anything (like some dummy div or even body for kicks) and then just raise PreventUpdate() instead of returning a value.

without getting any input can we display the output to the div?

This would be useful if I just want to print and see what the Input looks like, helps learn how to use the Input. Problem is, only one callback allowed per output, so for every such variable I want to inspect I have to create a new output. Or, input all Inputs in the same callback and and check the …

you can prevent the output via raising a exception. import dash @app.callback( dash.dependencies.Output('button', 'style'), [ dash.dependencies.Input('button', 'n_clicks'), ] ) def update(n_clicks): if n_clicks == 0: raise dash.exceptions.PreventUpdate("cancel the…

I would like to bump up the topic of callbacks without outputs again because I discovered this to be a common use-case if you use Dash to communicate with other processes. One example that comes directly into my mind is if you communicate with a Redis server and want to write some values depending …

[image] mega Multiple outputs in Dash - Now Available! Dash Python mega Announcing multi output! Update multiple component props from a single callback! Try now: $ pip install dash==0.39.0 See more features in Dash 0.39.0 release notes: megaphone Dash 0.39.0…

@trav Thanks for the link but I can not see how this addresses the issue at hand :confused:

Necessity of creating a dummy div seems weird. What if I want to do something on timer and don’t need to return anything immediately?

Typically, you would poll updates using an interval component.

[image] Emil: Typically, you would poll updates using an interval component. You still need an Output e.g. a dummy div for this to work which is not a nice solution if you want to pass information to the Backend (e.g. Redis server).

App callback without an output

Dash Python

trav July 15, 2020, 2:42pm 23

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App callback without an output

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