keras-team/keras · error · ValueError

The `data_format` argument must be one of {'channels_first',

Error message

The `data_format` argument must be one of {'channels_first', 'channels_last'}. Received: data_format={data_format}

What it means

Error "The `data_format` argument must be one of {'channels_first', 'channels_last'}. Received: data_format={data_format}" thrown in keras-team/keras.

Source

Thrown at keras/src/backend/config.py:173

        data_format: string. `'channels_first'` or `'channels_last'`.

    Examples:

    >>> keras.config.image_data_format()
    'channels_last'

    >>> keras.config.set_image_data_format('channels_first')
    >>> keras.config.image_data_format()
    'channels_first'

    >>> # Set it back to `'channels_last'`
    >>> keras.config.set_image_data_format('channels_last')

    """
    global _IMAGE_DATA_FORMAT
    data_format = str(data_format).lower()
    if data_format not in {"channels_first", "channels_last"}:
        raise ValueError(
            "The `data_format` argument must be one of "
            "{'channels_first', 'channels_last'}. "
            f"Received: data_format={data_format}"
        )
    _IMAGE_DATA_FORMAT = data_format


@keras_export("keras.config.enable_flash_attention")
def enable_flash_attention():
    """Enable flash attention.

    Flash attention offers performance optimization for attention layers,
    making it especially useful for large language models (LLMs) that
    benefit from faster and more memory-efficient attention computations.

    Once enabled, supported layers like `MultiHeadAttention` will **attempt** to
    use flash attention for faster computations. By default, this feature is
    enabled.

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/backend/config.py:173 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/420299f72ba4107a. Report an issue: GitHub.