def tx_index( cls, verified_block_txids, verified_tx ):
        """
        Given a block's verified block txids and a verified transaction, 
        find out where it is in the list of txids (i.e. what's its index)?
        """
        tx_hash = cls.tx_hash( verified_tx )
        return verified_block_txids.index( tx_hash )
def tx_index ( cls , verified_block_txids , verified_tx ) : tx_hash = cls . tx_hash ( verified_tx ) return verified_block_txids . index ( tx_hash )
Given a block's verified block txids and a verified transaction, 
        find out where it is in the list of txids (i.e. what's its index)?