old_contents: from app import app
  
  if __name__ == '__main__':
      if app.config.HOST:
          app.run(host=app.config.HOST)
      else:
          app.run()
  
new_contents: from app import app
  
  if __name__ == '__main__':
      if app.config['HOST']:
          app.run(host=app.config.HOST)
      else:
          app.run()
  
subject: Access correct host value