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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 _find_unused_partition() -> RootPartitions: """ Find the currently-unused root partition to write to """

    which = subprocess.check_output(['ot-unused-partition']).strip()
    return {b'2': RootPartitions.TWO,
            b'3': RootPartitions.THREE}[which]