keras-team/keras · error · ValueError

`backward_layer` need to be a `keras.layers.Layer` instance.

Error message

`backward_layer` need to be a `keras.layers.Layer` instance. Received: {backward_layer}

What it means

Error "`backward_layer` need to be a `keras.layers.Layer` instance. Received: {backward_layer}" thrown in keras-team/keras.

Source

Thrown at keras/src/layers/rnn/bidirectional.py:100

    model.compile(loss='categorical_crossentropy', optimizer='rmsprop')
    ```
    """

    def __init__(
        self,
        layer,
        merge_mode="concat",
        weights=None,
        backward_layer=None,
        **kwargs,
    ):
        if not isinstance(layer, Layer):
            raise ValueError(
                "Please initialize `Bidirectional` layer with a "
                f"`keras.layers.Layer` instance. Received: {layer}"
            )
        if backward_layer is not None and not isinstance(backward_layer, Layer):
            raise ValueError(
                "`backward_layer` need to be a `keras.layers.Layer` "
                f"instance. Received: {backward_layer}"
            )
        if merge_mode not in ["sum", "mul", "ave", "concat", None]:
            raise ValueError(
                f"Invalid merge mode. Received: {merge_mode}. "
                "Merge mode should be one of "
                '{"sum", "mul", "ave", "concat", None}'
            )
        super().__init__(**kwargs)

        # Recreate the forward layer from the original layer config, so that it
        # will not carry over any state from the layer.
        config = serialization_lib.serialize_keras_object(layer)
        config["config"]["name"] = (
            f"forward_{utils.removeprefix(layer.name, 'forward_')}"
        )
        self.forward_layer = serialization_lib.deserialize_keras_object(config)

View on GitHub (pinned to 7a34a03db6)

When it happens

Trigger: Thrown at keras/src/layers/rnn/bidirectional.py:100 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/fd003b6d9c623f65. Report an issue: GitHub.