keras-team/keras · error · ValueError

Unknown loss function: '{loss_item}'.

Error message

Unknown loss function: '{loss_item}'.

What it means

Error "Unknown loss function: '{loss_item}'." thrown in keras-team/keras.

Source

Thrown at keras/src/distillation/distillation_loss.py:26

def _convert_loss_to_function(loss_item):
    """Convert a loss string identifier to a loss function.

    Arguments:
        loss_item: Either a string identifier, a loss function instance,
            or `None`.

    Returns:
        A loss function instance, or `None`.

    Raises:
        ValueError: If the loss string identifier is unknown.
    """
    if loss_item is None:
        return None
    elif isinstance(loss_item, str):
        loss_fn = keras.losses.get(loss_item)
        if loss_fn is None:
            raise ValueError(f"Unknown loss function: '{loss_item}'.")
        return loss_fn
    else:
        return loss_item


@keras_export("keras.distillation.DistillationLoss")
class DistillationLoss:
    """Base class for distillation loss computation.

    Distillation losses define how to compute the distillation loss
    between teacher and student outputs. Each loss implements a specific
    approach to knowledge transfer, from simple logits matching to feature-based
    distillation.

    To create custom distillation losses, subclass this class and
    override the `compute_loss` method.
    """

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/distillation/distillation_loss.py:26 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of keras-team/keras@7a34a03db6 (2026-08-25). Data as JSON: /api/errors/57da3cc280ccca96. Report an issue: GitHub.