Given the sequence of transactions in a block, turn them into a
        sequence of virtual chain operations.

        Return the list of successfully-parsed virtualchain transactions

def parse_block(self, block_id, txs):
        """
        Given the sequence of transactions in a block, turn them into a
        sequence of virtual chain operations.

        Return the list of successfully-parsed virtualchain transactions
        """
        ops = []
        for i in range(0,len(txs)):
            tx = txs[i]
            op = self.parse_transaction(block_id, tx)
            if op is not None:
                ops.append( op )
            
        return ops