Not working Plot.ly Dash example

gistfile1.txt

# -*- coding: utf-8 -*-
import dash
import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Output, Input

app = dash.Dash('')

app.layout = dcc.Dropdown(
        id='my-dropdown',
        options=[
            {'label': 'New York City', 'value': 'NYC'},
            {'label': 'Montreal', 'value': 'MTL'},
            {'label': 'San Francisco', 'value': 'SF'}
        ],
        value="MTL",
        multi=True)

if __name__ == '__main__':
    app.server.run(debug=True)