load_model() with custom layers, and custom layers in general

1. What should I do to make my custom layers available to be loaded using load_model()?

I used my custom layers in this repo both Spectrogram and Melspectrogram didn’t work for load_model().

Error message:

>>> keras.models.load_model('model_best.hdf5')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/models.py", line 140, in load_model
    model = model_from_config(model_config, custom_objects=custom_objects)
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/models.py", line 189, in model_from_config
    return layer_from_config(config, custom_objects=custom_objects)
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/utils/layer_utils.py", line 34, in layer_from_config
    return layer_class.from_config(config['config'])
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/models.py", line 1055, in from_config
    layer = get_or_create_layer(first_layer)
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/models.py", line 1039, in get_or_create_layer
    layer = layer_from_config(layer_data)
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/utils/layer_utils.py", line 33, in layer_from_config
    instantiate=False)
  File "/Users/gnu/anaconda/lib/python2.7/site-packages/keras/utils/generic_utils.py", line 16, in get_from_module
    str(identifier))
Exception: Invalid layer: Melspectrogram
>>>

1. In the same manner, I think we should update layer customising documentation. My questions would be

• if I have to use self.add_weight() method? or just appending them in self.trainable_weights is fine?
• What do I have to do with get_config() method? When and how are they used?
• How self.built is used?

[NumesSanguis]

For the people landing here by a Google search, the code we should use:

model = keras.models.load_model('temp_model.h5',
              custom_objects={'Melspectrogram':kapre.time_frequency.Melspectrogram})

as can be found on kapre’s Github page: https://github.com/keunwoochoi/kapre

[bstriner]

Models.py saves the layer configuration and the class name.

for layer in self.layers[0].layers:
                layer_config = {'class_name': layer.__class__.__name__,
                                'config': layer.get_config()}
                layers.append(layer_config)

layer_from_config instantiates the class given the name.

layer_class = get_from_module(class_name, globals(), 'layer',
                                      instantiate=False)

Custom objects are added to the globals.

  if custom_objects:
       for cls_key in custom_objects:
           globals()[cls_key] = custom_objects[cls_key]

So, if you’re crashing on get_from_module, pass in a dictionary from the string of the class name to the actual class so get_from_module can find your class. {"MyClass":MyClass}

In terms of what to put into get_config, that same information is sent to your constructor. So the keywords in your get_config should match the kwargs of your constructor.

def from_config(cls, config):
      '''This method is the reverse of get_config,
      capable of instantiating the same layer from the config
      dictionary. It does not handle layer connectivity
      (handled by Container), nor weights (handled by `set_weights`).
      # Arguments
          config: A Python dictionary, typically the
              output of get_config.
      '''
      return cls(**config)

https://github.com/fchollet/keras/blob/master/keras/utils/layer_utils.py