code: def start(self):
      if self.subapp is None:
          print(
              "No subcommand specified. Must specify one of: %s"
              % list(self.subcommands)
          )
          print()
          self.print_description()
          self.print_subcommands()
          self.exit(1)
      else:
          return self.subapp.start()
  
imports: from __future__ import print_function
  import errno
  import os.path
  import sys
  import json
  from traitlets.config.application import Application
  from jupyter_core.application import JupyterApp, base_flags, base_aliases
  from traitlets import Instance, Dict, Unicode, Bool, List
  from .None import __version__
  from .kernelspec import KernelSpecManager
label_desc: Use image node_id 1 for calling the KernelSpecApp obj's underlying member method code with example usage: obj.start() and returns: self