Tensor not iterable in MNIST Training.ipynb

[ianpdavies]

I'm trying to work through the MNIST Training notebook but am having trouble getting it to run as written. I think it may be because of a new TF version, or perhaps an uncaught error? Specifically, in cell 7:

for head in heads:
    **logits, class_prob = head  # unpack**
    loss = tf.losses.softmax_cross_entropy(onehot_labels=y_data, logits=logits)
    loss_per_head.append(loss)
    train_per_head.append(optimizer.minimize(loss))
    correct_prediction = tf.equal(tf.argmax(class_prob, 1), tf.argmax(y_data, 1))
    accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
    accuracy_per_head.append(accuracy)

Returns the error "Tensor objects are not iterable when eager execution is not enabled". I'm using tf version 1.10.0. Anyone have tips on how to configure this to run correctly?