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def call(self, inputs): |
return tf.matmul(inputs, self.w) + self.b |
def get_config(self): |
config = super(CustomLayer, self).get_config() |
config.update({"units": self.units}) |
return config |
def custom_activation(x): |
return tf.nn.tanh(x) ** 2 |
# Make a model with the CustomLayer and custom_activation |
inputs = keras.Input((32,)) |
x = CustomLayer(32)(inputs) |
outputs = keras.layers.Activation(custom_activation)(x) |
model = keras.Model(inputs, outputs) |
# Retrieve the config |
config = model.get_config() |
# At loading time, register the custom objects with a `custom_object_scope`: |
custom_objects = {"CustomLayer": CustomLayer, "custom_activation": custom_activation} |
with keras.utils.custom_object_scope(custom_objects): |
new_model = keras.Model.from_config(config) |
In-memory model cloning |
You can also do in-memory cloning of a model via tf.keras.models.clone_model(). This is equivalent to getting the config then recreating the model from its config (so it does not preserve compilation information or layer weights values). |
Example: |
with keras.utils.custom_object_scope(custom_objects): |
new_model = keras.models.clone_model(model) |
Saving & loading only the model's weights values |
You can choose to only save & load a model's weights. This can be useful if: |
You only need the model for inference: in this case you won't need to restart training, so you don't need the compilation information or optimizer state. |
You are doing transfer learning: in this case you will be training a new model reusing the state of a prior model, so you don't need the compilation information of the prior model. |
APIs for in-memory weight transfer |
Weights can be copied between different objects by using get_weights and set_weights: |
tf.keras.layers.Layer.get_weights(): Returns a list of numpy arrays. |
tf.keras.layers.Layer.set_weights(): Sets the model weights to the values in the weights argument. |
Examples below. |
Transfering weights from one layer to another, in memory |
def create_layer(): |
layer = keras.layers.Dense(64, activation="relu", name="dense_2") |
layer.build((None, 784)) |
return layer |
layer_1 = create_layer() |
layer_2 = create_layer() |
# Copy weights from layer 1 to layer 2 |
layer_2.set_weights(layer_1.get_weights()) |
Transfering weights from one model to another model with a compatible architecture, in memory |
# Create a simple functional model |
inputs = keras.Input(shape=(784,), name="digits") |
x = keras.layers.Dense(64, activation="relu", name="dense_1")(inputs) |
x = keras.layers.Dense(64, activation="relu", name="dense_2")(x) |
outputs = keras.layers.Dense(10, name="predictions")(x) |
functional_model = keras.Model(inputs=inputs, outputs=outputs, name="3_layer_mlp") |
# Define a subclassed model with the same architecture |
class SubclassedModel(keras.Model): |
def __init__(self, output_dim, name=None): |
super(SubclassedModel, self).__init__(name=name) |
self.output_dim = output_dim |
self.dense_1 = keras.layers.Dense(64, activation="relu", name="dense_1") |
self.dense_2 = keras.layers.Dense(64, activation="relu", name="dense_2") |
self.dense_3 = keras.layers.Dense(output_dim, name="predictions") |
def call(self, inputs): |
x = self.dense_1(inputs) |
x = self.dense_2(x) |
x = self.dense_3(x) |
return x |
def get_config(self): |
return {"output_dim": self.output_dim, "name": self.name} |
subclassed_model = SubclassedModel(10) |
# Call the subclassed model once to create the weights. |
subclassed_model(tf.ones((1, 784))) |
# Copy weights from functional_model to subclassed_model. |
subclassed_model.set_weights(functional_model.get_weights()) |
assert len(functional_model.weights) == len(subclassed_model.weights) |
for a, b in zip(functional_model.weights, subclassed_model.weights): |
np.testing.assert_allclose(a.numpy(), b.numpy()) |
The case of stateless layers |
Because stateless layers do not change the order or number of weights, models can have compatible architectures even if there are extra/missing stateless layers. |
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