dropdown_broken_example.py

import dash
import dash_html_components as html
import dash_core_components as dcc
from dash.dependencies import Input, Output, State, Event

app = dash.Dash()

app.config.supress_callback_exceptions=True

app.layout = html.Div([
    dcc.Location(id='url', refresh=False),
    dcc.Link('Go to Cities', href='/cities'), 
    html.Br(),
    dcc.Link('Go To Oceans', href='/oceans'),
    html.Br(),html.Br(),
    html.Div(id='page-content')])

@app.callback(Output('page-content', 'children'),[Input('url', 'pathname')])
def generate_layout(url):
    if url == '/cities':
        return html.Div([
            html.Label('Multi-Select Dropdown - Cities'),
            dcc.Dropdown(
                options=[
                    {'label': 'New York City', 'value': 'NYC'},
                    {'label': u'Montréal', 'value': 'MTL'},
                    {'label': 'San Francisco', 'value': 'SF'}
                ],
                multi=True,
                id='input_cities'
            ),
            html.Div(id='output_cities')
        ])
    elif url == '/oceans':
        return html.Div([
            html.Label('Multi-Select Dropdown - Oceans'),
            html.Div(children=[dcc.Dropdown(
                options=[
                    {'label': 'Pacific Ocean', 'value': 'pacific'},
                    {'label': 'Atlantic Ocean', 'value': 'atlantic'},
                    {'label': 'Indian Ocean', 'value': 'indian'}
                ],
                multi=True,
                id='input_oceans'
            )]),
            html.Div(id='output_oceans')
        ])
    else:
        return "404"


@app.callback(Output('output_cities', 'children'), [Input('input_cities', 'value')])
def display_output(value):
    return 'You have selected the city "{}"'.format(value)


@app.callback(Output('output_oceans', 'children'), [Input('input_oceans', 'value')])
def display_output(value):
    return 'You have selected the ocean "{}"'.format(value)


if __name__ == '__main__':
    app.run_server(debug=True, host='0.0.0.0')