code: def _get_backend(args):
      
      if args.backend == 'gatttool':
          backend = GatttoolBackend
      elif args.backend == 'bluepy':
          backend = BluepyBackend
      elif args.backend == 'pygatt':
          backend = PygattBackend
      else:
          raise Exception('unknown backend: {}'.format(args.backend))
      return backend
docs: Extract the backend class from the command line arguments.