App Callback for dropdown value when button is clicked

Dash Python
1

I’ve a dropdown options which populate the 1st value in the list when Dash is populated.

I created a Button such that when I click “Previous”, it will populate the (current value - 1) value in the dropdown value but I’m getting an error “TypeError Traceback (most recent call last)
TypeError: button_date_value() missing 2 required positional arguments: ‘available_options’ and ‘current’’”.

I’ve attached my code below. Please do let me know if I’m missing out something. Thank you!

app.layout = html.Div([
    dcc.Dropdown(
        id='dropdown',
        options=options, value = options[0]["value"], style ={'width':'80%','display': 'inline-block'}
        ),
        dcc.Dropdown(id = "dates",style ={'width':'80%','display': 'inline-block'}),
    html.Button("Previous", id = "Previous", n_clicks = 0), html.Button("Next", id = "Next", n_clicks = 0),
    dcc.Dropdown(id = "models", style ={'width':'80%','display': 'inline-block'}),
    html.Hr(), 
    
    dcc.Graph(id="graph", style={"height": 800}),    
    html.Hr()
])

@app.callback(
    dash.dependencies.Output("dates", "options"),
    [dash.dependencies.Input("dropdown", "value")])
def set_dates_options(selected_node):
    dates_model = [*models_changed[selected_node].keys()]
    to_return = [{"label": i, "value": i} for i in dates_model]
    return to_return

@app.callback(
    dash.dependencies.Output("dates", "value"),
    [dash.dependencies.Input("dates", "options")])
def set_dates_value(available_options):
    return available_options[0]["value"]

@app.callback(
    dash.dependencies.Output("dates", "value"),
    [dash.dependencies.Input("Previous", "n_clicks"),
     dash.dependencies.State("dates", "options"),
     dash.dependencies.State("dates", "value")])
def button_date_value(clicks, available_options, current):
    if clicks > 1:
        return available_options[current - 1]["value"]
2

in your code you have passed the Input and two State inside the same list.
your function can’t find those parameters as they are in a single list, just remove the list brackets or put the Inputs and State in different lists

@app.callback(
    dash.dependencies.Output("dates", "value"),
    dash.dependencies.Input("Previous", "n_clicks"),
    dash.dependencies.State("dates", "options"),
    dash.dependencies.State("dates", "value")
)
def button_date_value(clicks, available_options, current):
    if clicks > 1:
        return available_options[current - 1]["value"]
3

@atharvakatre thanks but I’m still getting the same error after removing the list brackets or put the Input and State in different lists

4

Maybe if you could share your entire code I could reproduce the error and check it