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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 block_start(self, previous_block):
 """Returns an ordered list of batches to inject at the beginning of the block. Can also return None if no batches should be injected. Args: previous_block (Block):
 The previous block. Returns: A list of batches to inject. """


        previous_header_bytes = previous_block.header
        previous_header = BlockHeader()
        previous_header.ParseFromString(previous_header_bytes)

        block_info = BlockInfo(
            block_num=previous_header.block_num,
            previous_block_id=previous_header.previous_block_id,
            signer_public_key=previous_header.signer_public_key,
            header_signature=previous_block.header_signature,
            timestamp=int(time.time()))

        return [self.create_batch(block_info)]