How to turn off "interval" event?

Dash Python
1

I’m running a subprocess with its stdout piped, reading it using an interval timer, and displaying the output. I’d like to turn off the timer when the subprocess completes.

I tried creating a callback with Output(interval_id, ‘interval’) that detects if the subprocess has exited, and returns a value to reset the interval timer to something that effectively turns it off. I’ve tried values of 0, -1, and None but the timer keeps on ticking. How do I disable it? Do I have to remove it from the Div?

Thanks!

1 Like
2

Hi @plevin

I don’t think there is a way to disable the interval at the moment, but I’ve added this functionality to the component library and created a pull request: https://github.com/plotly/dash-core-components/pull/66

I tried setting the timer to an insanely large number but that doesn’t seem to work either so I don’t have much advice to give you in the meantime until we get that addition merged and released.

Sorry for the inconvenience.

3

I am simply setting the interval to 60*60*1000 for an 1 hour interval when output ends, and when output end is not found, I am returning the default interval value. That works fine.

@app.callback(Output('refreshing-output', 'value'),
              events=[Event('interval-element', 'interval')])
def refresh_output():
    # refresh (...)
    return new_value

@app.callback(Output('interval-element', 'interval'),
              [Input('refreshing-output', 'value')])
def disable_interval(content: str):
    if finished(content):
        return 60*60*1000
    else:
        return 1 * 5000
2 Likes
4

This should work and it looks like @radekwlsk was able to make this work with 1 hour. From SO, it looks like the maximum value for interval is 2,147,483,647 (2^31-1)) so perhaps this was being set to a number larger than that.

5

Hi guys,

I had this same issue… I couldn’t solve it in an extremely elegant way, however I didn’t like the idea of leaving a process running in the background.

I did this:

@app.callback(Output('tab-output', 'children'), [Input('tabs', 'value')], events=[Event("interval-component","interval")])
def display_content(value ):
# refresh (...)
return 

@app.callback(Output("interval-start", "children"), [Input("start-timer", "n_clicks"), Input("stop-timer", "n_clicks")])
def start_interval(n_clicks, stop_clicks):
    if n_clicks - stop_clicks > 1:
        n_clicks = stop_clicks + 1
    if n_clicks > 0 and stop_clicks == None :
        return dcc.Interval(id="interval-component", interval=1 * 1000)
    if stop_clicks > 0:
        return "No timer"
    else:
        return "Not yet started"

Maybe instead of using the click logic I needed you can include the completion of your subprocess.
Interested in your thoughts @chriddyp

6

I’m not sure what you mean by “subprocess” or “process running in the background”. Interval doesn’t start a new process, it just fires your callbacks. In either case, the solution that you provided looks good. You could also even just update the interval property of the interval-component if it was displayed in the app.layout.

7

This only worked, when I’ve added:

events=[Event('interval-data', 'interval')]

to the second callback, that switches off the interval. Basically it is listening to its own events.

8

Has there been any change in the Interval functionality since the last message above?
I’d like to be able to stop and start the Interval at will.

I have a live updating chart that I would like to have the option of suspending if the user wants to.

Thanks.

9

This was fixed a few months ago and has been available in dash-core-components since version 0.43.0. You can now write a callback that targets the disabled prop of your Interval.

10

Thanks for your reply,
Is there an example available that shows how to do this?
Thanks

11

@vidapura Something like this:

import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output, State

app = dash.Dash()

app.layout = html.Div(
    [
        dcc.Interval(id="interval"),
        html.P(id="output"),
        html.Button("toggle interval", id="button"),
    ]
)


@app.callback(
    Output("interval", "disabled"),
    [Input("button", "n_clicks")],
    [State("interval", "disabled")],
)
def toggle_interval(n, disabled):
    if n:
        return not disabled
    return disabled


@app.callback(Output("output", "children"), [Input("interval", "n_intervals")])
def display_count(n):
    return f"Interval has fired {n} times"


if __name__ == "__main__":
    app.run_server(debug=True)
12

Hi Tom,
Thank you very much for taking the time to create this example for me.
I really appreciate it.

Thanks again

1 Like
14

Note - As per the dcc.Interval documentation, there are two properties that can be used to turn off dcc.Interval:
disabled ( boolean ; optional): If True, the counter will no longer update

max_intervals ( number ; default -1 ): Number of times the interval will be fired. If -1, then the interval has no limit (the default) and if 0 then the interval stops running.