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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_backend(args):
 """Extract the backend class from the command line arguments."""

    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