code: def find_layer_idx(model, layer_name):
      
      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
docs: 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.