python 3.x - Dash Callback function not responding; Error: Duplicate Callback Output

Question

I am trying to create a dashboard consisting of 8 buttons, each of which corresponds to a filtered df and 4 dropdowns. The attempt was to take the filtered df according to the triggered button and use 4 columns of the df for 'options' of 4 different dcc.dropdown. But dash shows this error message:

In the callback for output(s):
MBD.options
Urbanity.options
Outlet.options
Chain.options
Output 1 (Urbanity.options) is already in use.
Any given output can only have one callback that sets it.
To resolve this situation, try combining these into
one callback function, distinguishing the trigger
by using dash.callback_context if necessary.

My callback is:

@app.callback([Output('MBD', 'options'), Output('Urbanity', 'options'), Output('Outlet', 'options'),
           Output('Chain', 'options')],
           [Input('all','id'), Input('fmcg','id'), Input('bev','id'), Input('tob','id'),
           Input('food','id'), Input('drug','id'), Input('liquor','id'), 
           Input('unilever','id')])
def update_dd(all_b, fmcg_b, bev_b, tob_b, food_b, drug_b, liq_b, unil_b):
    ctx = dash.callback_context
    dff = pd.DataFrame()

if not ctx.triggered:
    button_id  = 'all.id'
else:
    button_id = ctx.triggered[0]['prop_id']
if button_id == 'all.id' :
    dff = alloutlet_df.copy()
elif button_id == 'fmcg.id':
    dff = fmcg_df.copy()
elif button_id == 'bev.id':
    dff = bev_df.copy()
elif button_id == 'tob.id':
    dff = tob_df.copy()
elif button_id == 'food.id':
    dff = food_df.copy()
elif button_id == 'drug.id':
    dff = drug_df.copy()
elif button_id == 'liquor.id':
    dff = liquor_df.copy()
elif button_id == 'unilever.id':
    dff = unilever_df.copy()
else:
    dff = df.copy()


mbd_opt = {'label':dff['Region'].unique(), 'value':dff['Region'].unique()} 
urb_opt = {'label':dff['Urbanity'].unique(), 'value': dff['Urbanity'].unique()} 
out_opt = {'label':dff['Outype_panel'].unique(), 'value':dff['Outype_panel'].unique()} 
chain_opt = {'label':dff['CHAIN'].unique(), 'value':dff['CHAIN'].unique()} 
return [mbd_opt, urb_opt, out_opt, chain_opt]

question from:https://stackoverflow.com/questions/65941225/dash-callback-function-not-responding-error-duplicate-callback-output

Answer 1

The error tells you the problem:

Any given output can only have one callback that sets it.

You've only shared one callback here, but there must be another one that's outputting to the same ID and prop combination. You'll have to rework how your callbacks are set up to make sure that doesn't happen.