'Given a block, ungroup the transactions in it.
Args:
block_id (str): the id of the block in progress.
transactions (list(dict)): transactions of the block in
progress.
Returns:
``None`` if the block has been already voted, an iterator that
yields a transaction, block id, and the total number of
transactions contained in the block otherwise.'

def ungroup(self, block_id, transactions):

    num_tx = len(transactions)
    for tx in transactions:
        (yield (tx, block_id, num_tx))
