Percentage of times that predictions matches labels on non-0s.

def padded_accuracy(predictions,
                    labels,
                    weights_fn=common_layers.weights_nonzero):
  """Percentage of times that predictions matches labels on non-0s."""
  # If the last dimension is 1 then we're using L1/L2 loss.
  if common_layers.shape_list(predictions)[-1] == 1:
    return rounding_accuracy(predictions, labels, weights_fn=weights_fn)
  with tf.variable_scope("padded_accuracy", values=[predictions, labels]):
    padded_predictions, padded_labels = common_layers.pad_with_zeros(
        predictions, labels)
    weights = weights_fn(padded_labels)
    outputs = tf.to_int32(tf.argmax(padded_predictions, axis=-1))
    padded_labels = tf.to_int32(padded_labels)
    return tf.to_float(tf.equal(outputs, padded_labels)), weights