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# Just for demonstration purposes.
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img_inputs = keras.Input(shape=(32, 32, 3))
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The inputs that is returned contains information about the shape and dtype of the input data that you feed to your model. Here's the shape:
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inputs.shape
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TensorShape([None, 784])
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Here's the dtype:
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inputs.dtype
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tf.float32
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You create a new node in the graph of layers by calling a layer on this inputs object:
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dense = layers.Dense(64, activation="relu")
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x = dense(inputs)
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The "layer call" action is like drawing an arrow from "inputs" to this layer you created. You're "passing" the inputs to the dense layer, and you get x as the output.
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Let's add a few more layers to the graph of layers:
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x = layers.Dense(64, activation="relu")(x)
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outputs = layers.Dense(10)(x)
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At this point, you can create a Model by specifying its inputs and outputs in the graph of layers:
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model = keras.Model(inputs=inputs, outputs=outputs, name="mnist_model")
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Let's check out what the model summary looks like:
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model.summary()
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Model: "mnist_model"
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_________________________________________________________________
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Layer (type) Output Shape Param #
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=================================================================
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input_1 (InputLayer) [(None, 784)] 0
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_________________________________________________________________
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dense (Dense) (None, 64) 50240
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_________________________________________________________________
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dense_1 (Dense) (None, 64) 4160
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_________________________________________________________________
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dense_2 (Dense) (None, 10) 650
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=================================================================
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Total params: 55,050
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Trainable params: 55,050
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Non-trainable params: 0
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_________________________________________________________________
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You can also plot the model as a graph:
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keras.utils.plot_model(model, "my_first_model.png")
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png
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And, optionally, display the input and output shapes of each layer in the plotted graph:
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keras.utils.plot_model(model, "my_first_model_with_shape_info.png", show_shapes=True)
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png
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This figure and the code are almost identical. In the code version, the connection arrows are replaced by the call operation.
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A "graph of layers" is an intuitive mental image for a deep learning model, and the functional API is a way to create models that closely mirrors this.
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Training, evaluation, and inference
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Training, evaluation, and inference work exactly in the same way for models built using the functional API as for Sequential models.
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The Model class offers a built-in training loop (the fit() method) and a built-in evaluation loop (the evaluate() method). Note that you can easily customize these loops to implement training routines beyond supervised learning (e.g. GANs).
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Here, load the MNIST image data, reshape it into vectors, fit the model on the data (while monitoring performance on a validation split), then evaluate the model on the test data:
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(x_train, y_train), (x_test, y_test) = keras.datasets.mnist.load_data()
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x_train = x_train.reshape(60000, 784).astype("float32") / 255
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x_test = x_test.reshape(10000, 784).astype("float32") / 255
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model.compile(
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loss=keras.losses.SparseCategoricalCrossentropy(from_logits=True),
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optimizer=keras.optimizers.RMSprop(),
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metrics=["accuracy"],
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)
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history = model.fit(x_train, y_train, batch_size=64, epochs=2, validation_split=0.2)
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test_scores = model.evaluate(x_test, y_test, verbose=2)
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print("Test loss:", test_scores[0])
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print("Test accuracy:", test_scores[1])
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Epoch 1/2
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750/750 [==============================] - 2s 2ms/step - loss: 0.5648 - accuracy: 0.8473 - val_loss: 0.1793 - val_accuracy: 0.9474
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Epoch 2/2
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750/750 [==============================] - 1s 1ms/step - loss: 0.1686 - accuracy: 0.9506 - val_loss: 0.1398 - val_accuracy: 0.9576
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313/313 - 0s - loss: 0.1401 - accuracy: 0.9580
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Test loss: 0.14005452394485474
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Test accuracy: 0.9580000042915344
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For further reading, see the training and evaluation guide.
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Save and serialize
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Saving the model and serialization work the same way for models built using the functional API as they do for Sequential models. The standard way to save a functional model is to call model.save() to save the entire model as a single file. You can later recreate the same model from this file, even if the code that built the model is no longer available.
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This saved file includes the: - model architecture - model weight values (that were learned during training) - model training config, if any (as passed to compile) - optimizer and its state, if any (to restart training where you left off)
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model.save("path_to_my_model")
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del model
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# Recreate the exact same model purely from the file:
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model = keras.models.load_model("path_to_my_model")
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INFO:tensorflow:Assets written to: path_to_my_model/assets
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For details, read the model serialization & saving guide.
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