Error when using multiple output

Dash Python
1

Hi i am getting this error while doing the multiple output to change option and value in dropdown component.

the code:

app.layout = html.Div([
dcc.Input(id=‘device-input’,value=’’),
html.Button(‘Add Device’,id=‘add-device’),

dcc.Dropdown(
id='device-dropdown',
options=[],
value=[],
multi=True,
  )

])

@app.callback(
[Output(‘device-dropdown’, ‘options’), Output(‘device-dropdown’, ‘value’)],
[Input(‘add-device’,‘n_clicks’)],
[State(‘device-input’, ‘value’), State(‘device-dropdown’, ‘options’),State(‘device-dropdown’, ‘value’)])
def callback(n_clicks, input_value, current_options, device_list):

if not input_value:
    return current_options

if input_value not in device_list:
    device_list.append(input_value)
current_options.append({'label': input_value, 'value': input_value})
return (current_options, device_list)

The error:

Traceback (most recent call last):
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 2328, in call
return self.wsgi_app(environ, start_response)
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 2314, in wsgi_app
response = self.handle_exception(e)
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 1760, in handle_exception
reraise(exc_type, exc_value, tb)
File “/usr/local/lib/python3.7/site-packages/flask/_compat.py”, line 36, in reraise
raise value
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 2311, in wsgi_app
response = self.full_dispatch_request()
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 1834, in full_dispatch_request
rv = self.handle_user_exception(e)
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 1737, in handle_user_exception
reraise(exc_type, exc_value, tb)
File “/usr/local/lib/python3.7/site-packages/flask/_compat.py”, line 36, in reraise
raise value
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 1832, in full_dispatch_request
rv = self.dispatch_request()
File “/usr/local/lib/python3.7/site-packages/flask/app.py”, line 1818, in dispatch_request
return self.view_functionsrule.endpoint
File “/usr/local/lib/python3.7/site-packages/dash/dash.py”, line 1152, in dispatch
response.set_data(self.callback_map[output]‘callback’)
File “/usr/local/lib/python3.7/site-packages/dash/dash.py”, line 1055, in add_context
len(output_value)
dash.exceptions.InvalidCallbackReturnValue: Invalid number of output values for …device-dropdown.options…device-dropdown.value…
Expected 2 got 0

2

Try the following code. Edited from your code…

import dash
import dash_core_components as dcc
import dash_html_components as html

from dash.dependencies import Output, Input, State

app = dash.Dash(__name__)

app.layout = html.Div([
		dcc.Input(id='device-input',value=''),
		html.Button('Add Device',id='add-device'),

		dcc.Dropdown(
			id='device-dropdown',
			options=[],
			value=[],
			multi=True,
		  )
	])

@app.callback(
	[Output('device-dropdown', 'options'), Output('device-dropdown', 'value')],
	[Input('add-device','n_clicks')],
	[State('device-input', 'value'), State('device-dropdown', 'options'),State('device-dropdown', 'value')])
def callback(n_clicks, input_value, current_options, device_list):
	
	if not input_value:
	    return current_options, device_list

	else:
		if device_list:
			if input_value not in device_list:
				device_list.append(input_value)
				current_options.append({'label': input_value, 'value': input_value})

		else:
			device_list.append(input_value)
			current_options.append({'label': input_value, 'value': input_value})


		return current_options, device_list


if __name__ == '__main__':
    app.run_server(debug=True, port=1234)

hop that is what you want…