有没有办法在 Dash Plotly Python 中的开关打开时不断更新图形？

Question

I have a function that updates the figure of a graph using an algorithm, and a callback function to return the graph's figure (among many other things). This is the basic idea:

for i in range(0,5):
    time.sleep(0.1)
    randomfunction(i)
    return plot

How can I update the graph without breaking the loop? I've tried using yield instead of return to no avail as the callback does not expect a generator class to be output.

Answer 1

The standard approach in Dash would be to write the figure (or just the data) to a server side cache (eg a file on disk or a Redis cache) from within the loop,

for i in range(0,5):
    time.sleep(0.1)
    randomfunction(i)
    # write data to server side cache

and then use an Interval component to trigger a callback that reads from the cache and updates the graph. Something like,

@app.callback(Output("graph_id", "figure"), Input("interval_id", "n_intervals")):
def update_graph(_):
    data = ... # read data from server side cache
    figure = ...  # generate figure from data
    return figure

Answer 2

While the accepted answer certainly works, there is another way to do it for anyone who may want to do this without external storage.

There is a Dash Core Component called dcc.Interval that you can use to constantly trigger a callback, within which you can update your graph.

For example, set up a layout that has your graph's layout and the following:

import dash_core_components as dcc
dcc.Interval(id="refresh-graph-interval", disabled=False, interval=1000)

Then, in your callback:

from dash.exceptions import PreventUpdate

@app.callback(
    Output("graph", "figure"), 
    [Input("refresh-graph-interval", "n_intervals")]
)
def refresh_graph_interval_callback(n_intervals):
    if n_intervals is not None:
        for i in range(0,5):
            time.sleep(0.1)
            randomfunction(i)
            return plot
    raise PreventUpdate()