code: def start(self):
          
          super(JupyterTensorboardApp, self).start()
  
          # The above should have called a subcommand and raised NoStart; if we
          # get here, it didn't, so we should self.log.info a message.
          subcmds = ", ".join(sorted(self.subcommands))
          sys.exit("Please supply at least one subcommand: %s" % subcmds)
docs: Perform the App's actions as configured