Spliting a dash app into modules

app.py

from page_1 import *
from page_2 import *

server = app.server

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

page_1.py

from server import URL_TO_PAGE, app

URL_TO_PAGE['/page-1'] = html.Div([
    html.H1('Page 1'),
    dcc.Dropdown(
        id='page-1-dropdown',
        options=[{'label': i, 'value': i} for i in ['LA', 'NYC', 'MTL']],
        value='LA'
    ),
    html.Div(id='page-1-content'),
    html.Br(),
    dcc.Link('Go to Page 2', href='/page-2'),
    html.Br(),
    dcc.Link('Go back to home', href='/'),
])

@app.callback(dash.dependencies.Output('page-1-content', 'children'),
              [dash.dependencies.Input('page-1-dropdown', 'value')])
def page_1_dropdown(value):
    return 'You have selected "{}"'.format(value)

page_2.py

from server import URL_TO_PAGE, app

URL_TO_PAGE['/page-2'] = html.Div([
    html.H1('Page 2'),
    dcc.Dropdown(
        id='page-1-dropdown',
        options=[{'label': i, 'value': i} for i in ['LA', 'NYC', 'MTL']],
        value='LA'
    ),
    html.Div(id='page-1-content'),
    html.Br(),
    dcc.Link('Go to Page 2', href='/page-2'),
    html.Br(),
    dcc.Link('Go back to home', href='/'),
])

@app.callback(dash.dependencies.Output('page-2-content', 'children'),
              [dash.dependencies.Input('page-2-dropdown', 'value')])
def page_2_dropdown(value):
    return 'You have selected "{}"'.format(value)

server.py

import dash
import dash_core_components as dcc
import dash_html_components as html
external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
app.layout = html.Div([
    # represents the URL bar, doesn't render anything
    dcc.Location(id='url', refresh=False),
    dcc.Link('Navigate to "/"', href='/'),
    html.Br(),
    dcc.Link('Navigate to "/page-1"', href='/page-1'),
    dcc.Link('Navigate to "/page-2"', href='/page-2'),
    # content will be rendered in this element
    html.Div(id='page-content')
])

URL_TO_PAGE = {}
@app.callback(dash.dependencies.Output('page-content', 'children'),
              [dash.dependencies.Input('url', 'pathname')])
def display_page(url):
    return URL_TO_PAGE[url]