code: def start(self):
      if self.subapp is None:
          print(
              "No subcommand specified. Must specify one of: %s"
              % (self.subcommands.keys())
          )
          print()
          self.print_description()
          self.print_subcommands()
          self.exit(1)
      else:
          return self.subapp.start()
  
file_path: catboost/contrib/python/ipython/py2/IPython/core/historyapp.py
imports: from __future__ import print_function
  import os
  import sqlite3
  from traitlets.config.application import Application
  from IPython.core.application import BaseIPythonApplication
  from traitlets import Bool, Int, Dict
  from IPython.utils.io import ask_yes_no
label_desc: Use image node_id 1 for calling the HistoryApp obj's underlying member method code with example usage: obj.start() and returns: self