code: def block_start(self, previous_block):
          
  
          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)]
docs: 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.