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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 _expand_block(cls, block):
 """Deserializes a Block's header, and the header of its Batches. """

        cls._parse_header(BlockHeader, block)
        if 'batches' in block:
            block['batches'] = [cls._expand_batch(b) for b in block['batches']]
        return block