tf.keras.callbacks.Callback

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Abstract base class used to build new callbacks.

tf.keras.callbacks.Callback()

Callbacks can be passed to keras methods such as fit, evaluate, and predict in order to hook into the various stages of the model training and inference lifecycle.

To create a custom callback, subclass keras.callbacks.Callback and override the method associated with the stage of interest. See https://www.tensorflow.org/guide/keras/custom_callback for more information.

Example:

training_finished = False
class MyCallback(tf.keras.callbacks.Callback):
  def on_train_end(self, logs=None):
    global training_finished
    training_finished = True
model = tf.keras.Sequential([
    tf.keras.layers.Dense(1, input_shape=(1,))])
model.compile(loss='mean_squared_error')
model.fit(tf.constant([[1.0]]), tf.constant([[1.0]]),
          callbacks=[MyCallback()])
assert training_finished == True

If you want to use Callback objects in a custom training loop:

1. You should pack all your callbacks into a single callbacks.CallbackList so they can all be called together.
2. You will need to manually call all the on_* methods at the appropriate locations in your loop. Like this:

Example:

   callbacks =  tf.keras.callbacks.CallbackList([...])
   callbacks.append(...)
   callbacks.on_train_begin(...)
   for epoch in range(EPOCHS):
     callbacks.on_epoch_begin(epoch)
     for i, data in dataset.enumerate():
       callbacks.on_train_batch_begin(i)
       batch_logs = model.train_step(data)
       callbacks.on_train_batch_end(i, batch_logs)
     epoch_logs = ...
     callbacks.on_epoch_end(epoch, epoch_logs)
   final_logs=...
   callbacks.on_train_end(final_logs)

The logs dictionary that callback methods take as argument will contain keys for quantities relevant to the current batch or epoch (see method-specific docstrings).

Methods

on_batch_begin

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on_batch_begin(
    batch, logs=None
)

A backwards compatibility alias for on_train_batch_begin.

on_batch_end

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on_batch_end(
    batch, logs=None
)

A backwards compatibility alias for on_train_batch_end.

on_epoch_begin

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on_epoch_begin(
    epoch, logs=None
)

Called at the start of an epoch.

Subclasses should override for any actions to run. This function should only be called during TRAIN mode.

on_epoch_end

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on_epoch_end(
    epoch, logs=None
)

Called at the end of an epoch.

Subclasses should override for any actions to run. This function should only be called during TRAIN mode.

on_predict_batch_begin

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on_predict_batch_begin(
    batch, logs=None
)

Called at the beginning of a batch in predict methods.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_predict_batch_end

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on_predict_batch_end(
    batch, logs=None
)

Called at the end of a batch in predict methods.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_predict_begin

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on_predict_begin(
    logs=None
)

Called at the beginning of prediction.

Subclasses should override for any actions to run.

on_predict_end

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on_predict_end(
    logs=None
)

Called at the end of prediction.

Subclasses should override for any actions to run.

on_test_batch_begin

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on_test_batch_begin(
    batch, logs=None
)

Called at the beginning of a batch in evaluate methods.

Also called at the beginning of a validation batch in the fit methods, if validation data is provided.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_test_batch_end

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on_test_batch_end(
    batch, logs=None
)

Called at the end of a batch in evaluate methods.

Also called at the end of a validation batch in the fit methods, if validation data is provided.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_test_begin

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on_test_begin(
    logs=None
)

Called at the beginning of evaluation or validation.

Subclasses should override for any actions to run.

on_test_end

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on_test_end(
    logs=None
)

Called at the end of evaluation or validation.

Subclasses should override for any actions to run.

on_train_batch_begin

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on_train_batch_begin(
    batch, logs=None
)

Called at the beginning of a training batch in fit methods.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_train_batch_end

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on_train_batch_end(
    batch, logs=None
)

Called at the end of a training batch in fit methods.

Subclasses should override for any actions to run.

Note that if the steps_per_execution argument to compile in tf.keras.Model is set to N, this method will only be called every N batches.

on_train_begin

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on_train_begin(
    logs=None
)

Called at the beginning of training.

Subclasses should override for any actions to run.

on_train_end

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on_train_end(
    logs=None
)

Called at the end of training.

Subclasses should override for any actions to run.

set_model

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set_model(
    model
)

set_params

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set_params(
    params
)