dash-tutorial-8.py

import dash
import dash_core_components as dcc
import dash_html_components as html

app = dash.Dash()

all_options = {'America': ['New York City', 'San Francisco', 'Cincinnati'],
               'Canada': ['Montreal', 'Toronto', 'Ottawa']}

app.layout = html.Div([
    dcc.RadioItems(id='countries-dropdown',
                   options = [{'label': i, 'value': i} for i in all_options.keys()],
                   value='America'),

    html.Hr(),

    dcc.RadioItems(id='cities-dropdown'),

    html.Hr(),

    html.Div(id='display-selected-values')
])

@app.callback(
    dash.dependencies.Output('cities-dropdown', 'options'),
    [dash.dependencies.Input('countries-dropdown', 'value')])
def set_cities_option(selected_country):
    return [{'label': i, 'value': i} for i in all_options[selected_country]]

@app.callback(
    dash.dependencies.Output('cities-dropdown', 'value'),
    [dash.dependencies.Input('countries-dropdown', 'value')])
def set_cities_value(selected_country):
    return all_options[selected_country][0]

@app.callback(
    dash.dependencies.Output('display-selected-values', 'children'),
    [dash.dependencies.Input('countries-dropdown', 'value'),
     dash.dependencies.Input('cities-dropdown', 'value')])
def set_display_children(selected_country, selected_city):
    return '{} is a city in {}'.format(selected_city, selected_country)

if __name__ == '__main__':
    app.run_server()