# hard sample mining?

net = build_net()

for i in range(NUM_ITERATIONS):

    anchors, positives, negatives = next(batch_generator)

    loss = net.evaluate([anchors, positives, negatives])

    loss_and_data = zip(loss, anchors, positives, negatives)

    loss_and_data = sorted(loss_and_data)

    batch_for_weight_update = loss_and_data[:batch_size]

    loss_hard, anchors_hard, positives_hard, negatives_hard = zip(*batch_for_weight_update)

    stuff = net.train_on_batch([anchors_hard, positives_hard, negatives_hard])