Upgrading to dash 2.0

Posted on Tue 05 October 2021 in Python • Tagged with Python, Dash

I had some dashboards built in Python with Dash. They were using version 1.13.4 and I updated it to version 2.0.0. In addition to converting the imports, as explained in the migration guide, I also had to change state variables because I was getting the error:

ValueError: The state keyword argument may not be provided without the input keyword argument

I didn't understand the explanation in the migration guide. After reading the new documentation about callbacks, I've found that I had to change my app_callbacks. Previously, I had something like this:

@app.callback(
    Output(component_id='wl-plot', component_property='src'),
    [
        Input(component_id='sol-select', component_property='value'),
        Input(component_id='button-apply', component_property='n_clicks'),
    ],
    state=
    [
        State(component_id='base-dir', component_property='value'),
    ]
)

And I had to change it to this:

@app.callback(
    Output(component_id='wl-plot', component_property='src'),
    Input(component_id='sol-select', component_property='value'),
    Input(component_id='button-apply', component_property='n_clicks'),
    State(component_id='base-dir', component_property='value'),
)

So, basically, now you only have a list of Output, Input and State instances and you don need the state=....