Help: Just Creating a Button in code calls its callback, even when it's not clicked


I have 100 dynamically created buttons, each linked to its own callback via n_clicks_timestamp (also dynamically created). However the callbacks get called just on button creation even though they are not pressed yet. How can I avoid this?

This results in 100 callbacks one after the other, really slowing everything down.


Hey, Didn’t tried it but it should work:

from dash.exceptions import PreventUpdate

def button_click(n_clicks_timestamp)
    if n_click_timestamps is None:  # maybe if n_click_timestamp == 0:
        raise PreventUpdate
    Your stuff


This works but doesn’t avoid the Callback. I am talking about avoiding the callback entirely.

If this can’t be done, then I think this is a bug in Dash. If the click property hasn’t changed, there is no reason to alert the callback.

Why this matters: For an app hosted on a remote server, it introduces a lot of request/response activity from client to server, and adds a ton of unneeded latency if you have 100+ buttons. This can be easily seen in Chrome Developer Tools Network tab.


All callbacks are fired once when the app loads. This is the current default behaviour of the Dash renderer to ensure that the app starts from a valid state.

I can see why this is undesirable for a remotely hosted app with a large number of callbacks. It’s possible this may change in the future to avoid this performance hit, but I’m not aware of any specific plans.


There’s a pretty good explanation on github. Discussion around a possible breaking change in dash 1.x / 2.x

I’m personally most interested in the use case with localStorage