Feature request: optional callback

[davnat]

Would you consider adding an optional callback to st_autorefresh?

In my idea, the component should only refresh if the callback is None or if it returns True

[frankhuurman]

This would be a nice way to prevent unnecessary reruns! In my case I'm waiting for altered information from an external API, in case it's different than the previous value I'd like a widget to be refreshed.

Another cool feature would be to tie the refresh functionality to a specific widget so that it only triggers a refresh of that widget instead of the entire 'page' or app. That would be neat for st.metric widgets for example.

[kmcgrady]

Interesting @davnat ! Can you describe a use case here? I wonder whether conditionally including the auto refresh would solve it.

if callback():
  st_autorefresh(...)

This component specifically would force a rerun of the entire script until Streamlit offers a built-in functionality to implement callbacks (a la session state). Same with updating a single widget @frankhuurman. Something interesting for Streamlit to evolve into.

[davnat]

Thanks for commenting on this.

My use case is:

• poll an API and check if something changed
• if something changed, trigger a rerun

The problem with the solution you propose is that once the callback returns False the poll is stopped, and there's no way to restart it without a user action.

[kmcgrady]

Gotcha @davnat that's an interesting problem because the rerun trigger is essentially done from the frontend, which wouldn't be able to execute your function.

I think we might need to have an update to Streamlit Custom Components to enable such a feature. :-/ I'll be sure to send the feedback to them!