I have built an app with multiple dropdowns and a button, the output being a chart which depends on the dropdown values.

spline_rc_app = dash.Dash(__name__, external_stylesheets=[dbc.themes.LITERA])
spline_rc_app.layout =  html.Div([

              dcc.Dropdown(id = 'country'....)
              dbc.Button("Run",id='run_spline'...)
              html.Div(id='output', children =[])

])
@spline_rc_app.callback(Output('output', 'children', allow_duplicate=True), 
                        Input('run_spline', 'n_clicks'),
                        State('country', 'value'),
                        State('output', 'children'), 
                        prevent_initial_call=True
)
def add_chart(n_clicks, children, country): 
    if not n_clicks: 
        raise PreventUpdate

    data_cmt_country = eur_cmt_curves[country] ## this is giving an error on country, but if I replace by 'belgium', it is working well... 

....

Any idea how to access the dropdown value to filter a dataframe in the callback function..?

Thanks