Live Updating Components

The dccInterval Component

Components in Dash usually update through user interaction like
selecting a dropdown, dragging a slider, or hovering over points.

If you’re building an application for monitoring, you may want to update
components in your application every few seconds or minutes.

The dccInterval element allows you to update components
on a predefined interval. The n_intervals property is an integer that is
automatically incremented every time interval milliseconds pass.
You can listen to this variable inside your app’s callback to fire
the callback on a predefined interval.

This example pulls data from live satellite feeds and updates the graph
and the text every second.

Updates on Page Load

By default, Dash apps store the app.layout in memory. This ensures that the
layout is only computed once, when the app starts.

If you set app.layout to a function, then you can serve a dynamic layout
on every page load.

For example, if your app.layout looked like this:

then your app would display the time when the app was started.

If you change this to a function, then a new datetime will get computed
everytime you refresh the page. Give it a try:

Heads up! You need to write app.layout = serve_layout not app.layout = serve_layout().
That is, define app.layout to the actual function instance.

You can combine this with time-expiring caching
and serve a unique layout every hour or every day and serve the computed layout
from memory in between.