tensorflow/models · error · ValueError

Length of class_weights should be {}

Error message

Length of class_weights should be {}

What it means

Error "Length of class_weights should be {}" thrown in tensorflow/models.

Source

Thrown at official/vision/losses/maskrcnn_losses.py:197

    Args:
      class_outputs: a float tensor representing the class prediction for each
        box with a shape of [batch_size, num_boxes, num_classes].
      class_targets: a float tensor representing the class label for each box
        with a shape of [batch_size, num_boxes].
      class_weights: A float list containing the weight of each class.

    Returns:
      a scalar tensor representing total class loss.
    """
    with tf.name_scope('fast_rcnn_loss'):
      output_dtype = class_outputs.dtype
      num_classes = class_outputs.get_shape().as_list()[-1]
      class_weights = (
          class_weights if class_weights is not None else [1.0] * num_classes
      )
      if num_classes != len(class_weights):
        raise ValueError(
            'Length of class_weights should be {}'.format(num_classes)
        )

      class_weights = tf.constant(class_weights, dtype=output_dtype)

      class_targets_one_hot = tf.one_hot(
          tf.cast(class_targets, dtype=tf.int32),
          num_classes,
          dtype=class_outputs.dtype)
      if self._use_binary_cross_entropy:
        # (batch_size, num_boxes, num_classes)
        cross_entropy_loss = tf.nn.sigmoid_cross_entropy_with_logits(
            labels=class_targets_one_hot, logits=class_outputs)
        cross_entropy_loss *= class_weights
      else:
        # (batch_size, num_boxes)
        cross_entropy_loss = tf.nn.softmax_cross_entropy_with_logits(
            labels=class_targets_one_hot, logits=class_outputs)

View on GitHub (pinned to e006f5f0d5)

When it happens

Trigger: Thrown at official/vision/losses/maskrcnn_losses.py:197 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of tensorflow/models@e006f5f0d5 (2026-08-24). Data as JSON: /api/errors/e9b738643634eb15. Report an issue: GitHub.