code: def _do_debug(self, cmd, args):
          
          if not args:
              self.stdout.write('on' if self.debug else 'off')
              self.stdout.write('\n')
              return
          if len(args) > 1:
              self.stderr.write('debug: too many arguments: {}\n'.format(args))
              return
          action = args[0]
          if action == 'on':
              self.debug = True
          elif action == 'off':
              self.debug = False
          elif action == 'shell':
              return 'DEBUG'
          elif action == 'toggle':
              self.debug = not self.debug
              self.stdout.write('on' if self.debug else 'off')
              self.stdout.write('\n')
          else:
              self.stderr.write('debug: unrecognized argument: {}\n'.format(action))
docs: \
          Enter the debugging shell.
              debug               Show current debugging status, i.e, on/off.
              debug {on,off}      Turn on/off debugging info.
              debug shell         Enter debugging shell.
              debug toggle        Toggle current debugging status.