code: def handle_command_error(self, command, args, exc):
          
          verbosity = self.command_error_verbosity
          if verbosity == 'traceback':
              self.pretty_print_exc(command, exc, show_traceback=True)
          elif verbosity == 'debug':
              pdb.set_trace()
          elif verbosity == 'raise':
              raise exc
          elif verbosity == 'pretty':
              self.pretty_print_exc(command, exc)
          else:
              raise ValueError('Unexpected exception_verbosity: %s' %
                               verbosity)
docs: Depending on how the session is configured this will print
          information about an unhandled command exception or possibly jump
          to some other behavior like a debugger.