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...Predicting: start of batch 2; got log keys: []
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...Predicting: end of batch 2; got log keys: ['outputs']
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...Predicting: start of batch 3; got log keys: []
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...Predicting: end of batch 3; got log keys: ['outputs']
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...Predicting: start of batch 4; got log keys: []
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...Predicting: end of batch 4; got log keys: ['outputs']
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...Predicting: start of batch 5; got log keys: []
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...Predicting: end of batch 5; got log keys: ['outputs']
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...Predicting: start of batch 6; got log keys: []
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...Predicting: end of batch 6; got log keys: ['outputs']
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...Predicting: start of batch 7; got log keys: []
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...Predicting: end of batch 7; got log keys: ['outputs']
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Stop predicting; got log keys: []
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Usage of logs dict
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The logs dict contains the loss value, and all the metrics at the end of a batch or epoch. Example includes the loss and mean absolute error.
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class LossAndErrorPrintingCallback(keras.callbacks.Callback):
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def on_train_batch_end(self, batch, logs=None):
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print("For batch {}, loss is {:7.2f}.".format(batch, logs["loss"]))
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def on_test_batch_end(self, batch, logs=None):
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print("For batch {}, loss is {:7.2f}.".format(batch, logs["loss"]))
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def on_epoch_end(self, epoch, logs=None):
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print(
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"The average loss for epoch {} is {:7.2f} "
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"and mean absolute error is {:7.2f}.".format(
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epoch, logs["loss"], logs["mean_absolute_error"]
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)
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)
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model = get_model()
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model.fit(
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x_train,
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y_train,
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batch_size=128,
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epochs=2,
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verbose=0,
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callbacks=[LossAndErrorPrintingCallback()],
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)
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res = model.evaluate(
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x_test,
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y_test,
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batch_size=128,
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verbose=0,
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callbacks=[LossAndErrorPrintingCallback()],
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)
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For batch 0, loss is 32.45.
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For batch 1, loss is 393.79.
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For batch 2, loss is 272.00.
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For batch 3, loss is 206.95.
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For batch 4, loss is 167.29.
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For batch 5, loss is 140.41.
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For batch 6, loss is 121.19.
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For batch 7, loss is 109.21.
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The average loss for epoch 0 is 109.21 and mean absolute error is 5.83.
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For batch 0, loss is 5.94.
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For batch 1, loss is 5.73.
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For batch 2, loss is 5.50.
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For batch 3, loss is 5.38.
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For batch 4, loss is 5.16.
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For batch 5, loss is 5.19.
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For batch 6, loss is 5.64.
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For batch 7, loss is 7.05.
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The average loss for epoch 1 is 7.05 and mean absolute error is 2.14.
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For batch 0, loss is 40.89.
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For batch 1, loss is 42.12.
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For batch 2, loss is 41.42.
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For batch 3, loss is 42.10.
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For batch 4, loss is 42.05.
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For batch 5, loss is 42.91.
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For batch 6, loss is 43.05.
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For batch 7, loss is 42.94.
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Usage of self.model attribute
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In addition to receiving log information when one of their methods is called, callbacks have access to the model associated with the current round of training/evaluation/inference: self.model.
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Here are of few of the things you can do with self.model in a callback:
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Set self.model.stop_training = True to immediately interrupt training.
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Mutate hyperparameters of the optimizer (available as self.model.optimizer), such as self.model.optimizer.learning_rate.
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Save the model at period intervals.
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Record the output of model.predict() on a few test samples at the end of each epoch, to use as a sanity check during training.
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Extract visualizations of intermediate features at the end of each epoch, to monitor what the model is learning over time.
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etc.
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Let's see this in action in a couple of examples.
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Examples of Keras callback applications
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Early stopping at minimum loss
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This first example shows the creation of a Callback that stops training when the minimum of loss has been reached, by setting the attribute self.model.stop_training (boolean). Optionally, you can provide an argument patience to specify how many epochs we should wait before stopping after having reached a local minimum.
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tf.keras.callbacks.EarlyStopping provides a more complete and general implementation.
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import numpy as np
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class EarlyStoppingAtMinLoss(keras.callbacks.Callback):
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"""Stop training when the loss is at its min, i.e. the loss stops decreasing.
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