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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_layer_idx(model, layer_name):
 """Looks up the layer index corresponding to `layer_name` from `model`. Args: model: The `keras.models.Model` instance. layer_name: The name of the layer to lookup. Returns: The layer index if found. Raises an exception otherwise. """

    layer_idx = None
    for idx, layer in enumerate(model.layers):
        if layer.name == layer_name:
            layer_idx = idx
            break

    if layer_idx is None:
        raise ValueError("No layer with name '{}' within the model".format(layer_name))
    return layer_idx