old_contents: import datetime
  import time
  import random
  
  from dash.react import Dash
  from dash_html_components import Div
  from dash_core_components import Dropdown, Label
  
  dash = Dash(__name__)
  
  dash.layout = Div(id='wrapper', content=[
      Dropdown(id='source', options=[
          { 'value': 'a', 'label': 'Option a' },
          { 'value': 'b', 'label': 'Option b' }
      ]),
      Label(id='target', value='will update')
  ])
  
  
  def update_target(dropdown_data):
      return {
          'value': dropdown_data['props']['value']
      }
  
  
  dash.react('target', ['source'])(update_target)
  
  if __name__ == "__main__":
      dash.run_server(
          port=8050,
          debug=True,
          component_suites=[
              'dash_core_components',
              'dash_html_components'
          ]
      )
new_contents: import datetime
  import time
  import random
  
  from dash.react import Dash
  from dash_html_components import Div, Label
  from dash_core_components import Dropdown
  
  dash = Dash(__name__)
  
  dash.layout = Div(id='wrapper', content=[
      Dropdown(id='source', options=[
          {'value': 'a', 'label': 'Option a'},
          {'value': 'b', 'label': 'Option b'}
      ], value='a'),
      Label(id='target')
  ])
  
  
  def update_target(dropdown_data):
      return {
          'content': dropdown_data['value']
      }
  
  
  dash.react('target', ['source'])(update_target)
  
  dash.css.append_css({
      'external_url': (
          'https://rawgit.com/chriddyp/0247653a7c52feb4c48437e1c1837f75'
          '/raw/d4f178bc09f253251135aeb2141aa077300d1b3f/dash.css'
      )
  })
  
  # dash.scripts.config.serve_locally = True
  # dash.css.config.serve_locally = True
  
  if __name__ == "__main__":
      dash.run_server(
          port=8050,
          debug=True
      )
  
subject: update example