docs: def interactive():
      """Interactive classifier."""
      global n
      if request.method == 'GET' and request.args.get('heartbeat', '') != "":
          return request.args.get('heartbeat', '')
      if request.method == 'POST':
          logging.warning('POST to /interactive is deprecated. '
                          'Use /worker instead')
      else:
          # Page where the user can enter a recording
          return render_template('canvas.html')