code: # Copyright 2015 The TensorFlow Authors. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # ==============================================================================
  # pylint: disable=g-import-not-at-top
  # pylint: disable=g-classes-have-attributes
  """Callbacks: utilities called at certain points during model training.
  """
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import tensorflow as tf
  
  import collections
  import copy
  import csv
  import io
  import json
  import os
  import re
  import time
  
  import numpy as np
  import six
  from keras import backend as K
  from keras.distribute import distributed_file_utils
  from keras.distribute import worker_training_state
  from keras.optimizer_v2 import learning_rate_schedule
  from keras.utils import generic_utils
  from keras.utils import tf_utils
  from keras.utils import version_utils
  from keras.utils.data_utils import Sequence
  from keras.utils.generic_utils import Progbar
  from keras.utils.io_utils import path_to_string
  from keras.utils.mode_keys import ModeKeys
  from tensorflow.python.ops import summary_ops_v2
  from tensorflow.python.platform import tf_logging as logging
  from tensorflow.python.util.tf_export import keras_export
  from tensorflow.tools.docs import doc_controls
  
  try:
    import requests
  except ImportError:
    requests = None
  
  
  # Note: `configure_callbacks` is only used in TF1.
  def configure_callbacks(callbacks,
                          model,
                          do_validation=False,
                          batch_size=None,
                          epochs=None,
                          steps_per_epoch=None,
                          samples=None,
                          verbose=1,
                          count_mode='steps',
                          mode=ModeKeys.TRAIN):
    """Configures callbacks for use in various training loops.
  
    Args:
        callbacks: List of Callbacks.
        model: Model being trained.
        do_validation: Whether or not validation loop will be run.
        batch_size: Number of samples per batch.
        epochs: Number of epoch to train.
        steps_per_epoch: Number of batches to run per training epoch.
        samples: Number of training samples.
        verbose: int, 0 or 1. Keras logging verbosity to pass to ProgbarLogger.
        count_mode: One of 'steps' or 'samples'. Per-batch or per-sample count.
        mode: String. One of ModeKeys.TRAIN, ModeKeys.TEST, or ModeKeys.PREDICT.
          Which loop mode to configure callbacks for.
  
    Returns:
        Instance of CallbackList used to control all Callbacks.
    """
    # Check if callbacks have already been configured.
    if isinstance(callbacks, CallbackList):
      return callbacks
  
    if not callbacks:
      callbacks = []
  
    # Add additional callbacks during training.
    if mode == ModeKeys.TRAIN:
      model.history = History()
      callbacks = [BaseLogger()] + (callbacks or []) + [model.history]
      if verbose:
        callbacks.append(ProgbarLogger(count_mode))
    callback_list = CallbackList(callbacks)
  
    # Set callback model
    callback_model = model._get_callback_model()  # pylint: disable=protected-access
    callback_list.set_model(callback_model)
  
    set_callback_parameters(
        callback_list,
        model,
        do_validation=do_validation,
        batch_size=batch_size,
        epochs=epochs,
        steps_per_epoch=steps_per_epoch,
        samples=samples,
        verbose=verbose,
        mode=mode)
  
    callback_list.model.stop_training = False
    return callback_list
  
  
  def set_callback_parameters(callback_list,
                              model,
                              do_validation=False,
                              batch_size=None,
                              epochs=None,
                              steps_per_epoch=None,
                              samples=None,
                              verbose=1,
                              mode=ModeKeys.TRAIN):
    """Sets callback parameters.
  
    Args:
        callback_list: CallbackList instance.
        model: Model being trained.
        do_validation: Whether or not validation loop will be run.
        batch_size: Number of samples per batch.
        epochs: Number of epoch to train.
        steps_per_epoch: Number of batches to run per training epoch.
        samples: Number of training samples.
        verbose: int, 0 or 1. Keras logging verbosity to pass to ProgbarLogger.
        mode: String. One of ModeKeys.TRAIN, ModeKeys.TEST, or ModeKeys.PREDICT.
          Which loop mode to configure callbacks for.
    """
    metric_names = model.metrics_names
    for cbk in callback_list:
      if isinstance(cbk, (BaseLogger, ProgbarLogger)):
        cbk.stateful_metrics = metric_names[1:]  # Exclude `loss`
  
    # Set callback parameters
    callback_metrics = []
    # When we have deferred build scenario with iterator input, we will compile
    # when we standardize first batch of data.
    if mode != ModeKeys.PREDICT:
      callback_metrics = copy.copy(metric_names)
      if do_validation:
        callback_metrics += ['val_' + n for n in metric_names]
    callback_params = {
        'batch_size': batch_size,
        'epochs': epochs,
        'steps': steps_per_epoch,
        'samples': samples,
        'verbose': verbose,
        'do_validation': do_validation,
        'metrics': callback_metrics,
    }
    callback_list.set_params(callback_params)
  
  
  def _is_generator_like(data):
    """Checks if data is a generator, Sequence, or Iterator."""
    return (hasattr(data, '__next__') or hasattr(data, 'next') or isinstance(
        data, (Sequence, tf.compat.v1.data.Iterator, tf.data.Iterator)))
  
  
  def make_logs(model, logs, outputs, mode, prefix=''):
    """Computes logs for sending to `on_batch_end` methods."""
    metric_names = model.metrics_names
    if mode in {ModeKeys.TRAIN, ModeKeys.TEST} and metric_names:
      for label, output in zip(metric_names, outputs):
        logs[prefix + label] = output
    else:
      logs['outputs'] = outputs
    return logs
  
  
  @keras_export('keras.callbacks.CallbackList')
  class CallbackList(object):
    """Container abstracting a list of callbacks."""
  
    def __init__(self,
                 callbacks=None,
                 add_history=False,
                 add_progbar=False,
                 model=None,
                 **params):
      """Container for `Callback` instances.
  
      This object wraps a list of `Callback` instances, making it possible
      to call them all at once via a single endpoint
      (e.g. `callback_list.on_epoch_end(...)`).
  
      Args:
        callbacks: List of `Callback` instances.
        add_history: Whether a `History` callback should be added, if one does not
          already exist in the `callbacks` list.
        add_progbar: Whether a `ProgbarLogger` callback should be added, if one
          does not already exist in the `callbacks` list.
        model: The `Model` these callbacks are used with.
        **params: If provided, parameters will be passed to each `Callback` via
          `Callback.set_params`.
      """
      self.callbacks = tf.nest.flatten(callbacks) if callbacks else []
      self._add_default_callbacks(add_history, add_progbar)
  
      if model:
        self.set_model(model)
      if params:
        self.set_params(params)
  
      # Performance optimization: determines if batch hooks need to be called.
      # pylint: disable=protected-access
      self._should_call_train_batch_hooks = any(
          cb._implements_train_batch_hooks() for cb in self.callbacks)
      self._should_call_test_batch_hooks = any(
          cb._implements_test_batch_hooks() for cb in self.callbacks)
      self._should_call_predict_batch_hooks = any(
          cb._implements_predict_batch_hooks() for cb in self.callbacks)
      # pylint: enable=protected-access
  
      # Performance check: Check batch hooks for slowness compared to batch time.
      # Only run check for custom callbacks (i.e. not present in this file).
      self._check_timing = any([cbk.__class__.__name__ not in globals()
                                for cbk in self.callbacks])
      self._num_batches_for_timing_check = 5
      self._hook_times = {}
      self._batch_start_time = None
      self._batch_times = []
  
    def _add_default_callbacks(self, add_history, add_progbar):
      """Adds `Callback`s that are always present."""
      self._progbar = None
      self._history = None
  
      for cb in self.callbacks:
        if isinstance(cb, ProgbarLogger):
          self._progbar = cb
        elif isinstance(cb, History):
          self._history = cb
  
      if self._progbar is None and add_progbar:
        self._progbar = ProgbarLogger(count_mode='steps')
        self.callbacks.insert(0, self._progbar)
  
      if self._history is None and add_history:
        self._history = History()
        self.callbacks.append(self._history)
  
    def append(self, callback):
      self.callbacks.append(callback)
  
    def set_params(self, params):
      self.params = params
      for callback in self.callbacks:
        callback.set_params(params)
  
    def set_model(self, model):
      self.model = model
      if self._history:
        model.history = self._history
      for callback in self.callbacks:
        callback.set_model(model)
  
    def _call_batch_hook(self, mode, hook, batch, logs=None):
      """Helper function for all batch_{begin | end} methods."""
      if not self.callbacks:
        return
  
      if hook == 'begin':
        self._call_batch_begin_hook(mode, batch, logs)
      elif hook == 'end':
        self._call_batch_end_hook(mode, batch, logs)
      else:
        raise ValueError('Unrecognized hook: {}'.format(hook))
  
    def _call_batch_begin_hook(self, mode, batch, logs):
      """Helper function for `on_*_batch_begin` methods."""
      hook_name = 'on_{mode}_batch_begin'.format(mode=mode)
      self._call_batch_hook_helper(hook_name, batch, logs)
  
      if self._check_timing:
        self._batch_start_time = time.time()
  
    def _call_batch_end_hook(self, mode, batch, logs):
      """Helper function for `on_*_batch_end` methods."""
      hook_name = 'on_{mode}_batch_end'.format(mode=mode)
  
      if self._check_timing and batch >= 1:
        batch_time = time.time() - self._batch_start_time
        self._batch_times.append(batch_time)
  
      self._call_batch_hook_helper(hook_name, batch, logs)
  
      if len(self._batch_times) >= self._num_batches_for_timing_check:
        end_hook_name = hook_name
        begin_hook_name = 'on_{mode}_batch_begin'.format(mode=mode)
        avg_batch_time = sum(self._batch_times) / len(self._batch_times)
        avg_end_hook_time = sum(self._hook_times[end_hook_name]) / len(
            self._hook_times[end_hook_name])
        avg_begin_hook_time = sum(self._hook_times[begin_hook_name]) / len(
            self._hook_times[begin_hook_name])
  
        threshold_time = 1.0 * avg_batch_time
        warning_msg = ('Callback method `{hook}` is slow compared to '
                       'the batch time (batch time: {batch_time:.4f}s vs '
                       '`{hook}` time: {hook_time:.4f}s). Check your callbacks.')
        if avg_begin_hook_time > threshold_time:
          logging.warning(warning_msg.format(
              hook=begin_hook_name,
              batch_time=avg_batch_time,
              hook_time=avg_begin_hook_time))
        if avg_end_hook_time > threshold_time:
          logging.warning(warning_msg.format(
              hook=end_hook_name,
              batch_time=avg_batch_time,
              hook_time=avg_end_hook_time))
        self._check_timing = False
        self._batch_start_time = None
        self._batch_times = []
        self._hook_times = {}
  
    def _call_batch_hook_helper(self, hook_name, batch, logs):
      """Helper function for `on_*_batch_*` methods."""
      logs = logs or {}
      numpy_logs = None
      if self._check_timing:
        start_time = time.time()
  
      for callback in self.callbacks:
        hook = getattr(callback, hook_name)
        if getattr(callback, '_supports_tf_logs', False):
          hook(batch, logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          hook(batch, numpy_logs)
  
      if self._check_timing:
        if hook_name not in self._hook_times:
          self._hook_times[hook_name] = []
        self._hook_times[hook_name].append(time.time() - start_time)
  
    def _call_begin_hook(self, mode):
      """Helper function for on_{train|test|predict}_begin methods."""
      if mode == ModeKeys.TRAIN:
        self.on_train_begin()
      elif mode == ModeKeys.TEST:
        self.on_test_begin()
      else:
        self.on_predict_begin()
  
    def _call_end_hook(self, mode):
      """Helper function for on_{train|test|predict}_end methods."""
      if mode == ModeKeys.TRAIN:
        self.on_train_end()
      elif mode == ModeKeys.TEST:
        self.on_test_end()
      else:
        self.on_predict_end()
  
    def on_batch_begin(self, batch, logs=None):
      if self._should_call_train_batch_hooks:
        self._call_batch_hook(ModeKeys.TRAIN, 'begin', batch, logs=logs)
  
    def on_batch_end(self, batch, logs=None):
      if self._should_call_train_batch_hooks:
        self._call_batch_hook(ModeKeys.TRAIN, 'end', batch, logs=logs)
  
    def on_epoch_begin(self, epoch, logs=None):
      """Calls the `on_epoch_begin` methods of its callbacks.
  
      This function should only be called during TRAIN mode.
  
      Args:
          epoch: Integer, index of epoch.
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_epoch_begin(epoch, logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_epoch_begin(epoch, numpy_logs)
  
    def on_epoch_end(self, epoch, logs=None):
      """Calls the `on_epoch_end` methods of its callbacks.
  
      This function should only be called during TRAIN mode.
  
      Args:
          epoch: Integer, index of epoch.
          logs: Dict, metric results for this training epoch, and for the
            validation epoch if validation is performed. Validation result keys
            are prefixed with `val_`.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_epoch_end(epoch, logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_epoch_end(epoch, numpy_logs)
  
    def on_train_batch_begin(self, batch, logs=None):
      """Calls the `on_train_batch_begin` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.train_step`. Typically,
            the values of the `Model`'s metrics are returned.  Example:
            `{'loss': 0.2, 'accuracy': 0.7}`.
      """
      if self._should_call_train_batch_hooks:
        self._call_batch_hook(ModeKeys.TRAIN, 'begin', batch, logs=logs)
  
    def on_train_batch_end(self, batch, logs=None):
      """Calls the `on_train_batch_end` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
      if self._should_call_train_batch_hooks:
        self._call_batch_hook(ModeKeys.TRAIN, 'end', batch, logs=logs)
  
    def on_test_batch_begin(self, batch, logs=None):
      """Calls the `on_test_batch_begin` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.test_step`. Typically,
            the values of the `Model`'s metrics are returned.  Example:
            `{'loss': 0.2, 'accuracy': 0.7}`.
      """
      if self._should_call_test_batch_hooks:
        self._call_batch_hook(ModeKeys.TEST, 'begin', batch, logs=logs)
  
    def on_test_batch_end(self, batch, logs=None):
      """Calls the `on_test_batch_end` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
      if self._should_call_test_batch_hooks:
        self._call_batch_hook(ModeKeys.TEST, 'end', batch, logs=logs)
  
    def on_predict_batch_begin(self, batch, logs=None):
      """Calls the `on_predict_batch_begin` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.predict_step`,
            it typically returns a dict with a key 'outputs' containing
            the model's outputs.
      """
      if self._should_call_predict_batch_hooks:
        self._call_batch_hook(ModeKeys.PREDICT, 'begin', batch, logs=logs)
  
    def on_predict_batch_end(self, batch, logs=None):
      """Calls the `on_predict_batch_end` methods of its callbacks.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
      if self._should_call_predict_batch_hooks:
        self._call_batch_hook(ModeKeys.PREDICT, 'end', batch, logs=logs)
  
    def on_train_begin(self, logs=None):
      """Calls the `on_train_begin` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_train_begin(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_train_begin(numpy_logs)
  
    def on_train_end(self, logs=None):
      """Calls the `on_train_end` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_train_end(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_train_end(numpy_logs)
  
    def on_test_begin(self, logs=None):
      """Calls the `on_test_begin` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_test_begin(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_test_begin(numpy_logs)
  
    def on_test_end(self, logs=None):
      """Calls the `on_test_end` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_test_end(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_test_end(numpy_logs)
  
    def on_predict_begin(self, logs=None):
      """Calls the 'on_predict_begin` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_predict_begin(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_predict_begin(numpy_logs)
  
    def on_predict_end(self, logs=None):
      """Calls the `on_predict_end` methods of its callbacks.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
      logs = logs or {}
      numpy_logs = None
      for callback in self.callbacks:
        if getattr(callback, '_supports_tf_logs', False):
          callback.on_predict_end(logs)
        else:
          if numpy_logs is None:  # Only convert once.
            numpy_logs = tf_utils.to_numpy_or_python_type(logs)
          callback.on_predict_end(numpy_logs)
  
    def __iter__(self):
      return iter(self.callbacks)
  
  
  @keras_export('keras.callbacks.Callback')
  class Callback(object):
    """Abstract base class used to build new callbacks.
  
    Attributes:
        params: Dict. Training parameters
            (eg. verbosity, batch size, number of epochs...).
        model: Instance of `keras.models.Model`.
            Reference of the model being trained.
  
    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).
    """
  
    def __init__(self):
      self.validation_data = None  # pylint: disable=g-missing-from-attributes
      self.model = None
      # Whether this Callback should only run on the chief worker in a
      # Multi-Worker setting.
      # TODO(omalleyt): Make this attr public once solution is stable.
      self._chief_worker_only = None
      self._supports_tf_logs = False
  
    def set_params(self, params):
      self.params = params
  
    def set_model(self, model):
      self.model = model
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_batch_begin(self, batch, logs=None):
      """A backwards compatibility alias for `on_train_batch_begin`."""
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_batch_end(self, batch, logs=None):
      """A backwards compatibility alias for `on_train_batch_end`."""
  
    @doc_controls.for_subclass_implementers
    def on_epoch_begin(self, 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.
  
      Args:
          epoch: Integer, index of epoch.
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_epoch_end(self, 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.
  
      Args:
          epoch: Integer, index of epoch.
          logs: Dict, metric results for this training epoch, and for the
            validation epoch if validation is performed. Validation result keys
            are prefixed with `val_`. For training epoch, the values of the
           `Model`'s metrics are returned. Example : `{'loss': 0.2, 'acc': 0.7}`.
      """
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_train_batch_begin(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.train_step`. Typically,
            the values of the `Model`'s metrics are returned.  Example:
            `{'loss': 0.2, 'accuracy': 0.7}`.
      """
      # For backwards compatibility.
      self.on_batch_begin(batch, logs=logs)
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_train_batch_end(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
      # For backwards compatibility.
      self.on_batch_end(batch, logs=logs)
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_test_batch_begin(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.test_step`. Typically,
            the values of the `Model`'s metrics are returned.  Example:
            `{'loss': 0.2, 'accuracy': 0.7}`.
      """
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_test_batch_end(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_predict_batch_begin(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict, contains the return value of `model.predict_step`,
            it typically returns a dict with a key 'outputs' containing
            the model's outputs.
      """
  
    @doc_controls.for_subclass_implementers
    @generic_utils.default
    def on_predict_batch_end(self, 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.
  
      Args:
          batch: Integer, index of batch within the current epoch.
          logs: Dict. Aggregated metric results up until this batch.
      """
  
    @doc_controls.for_subclass_implementers
    def on_train_begin(self, logs=None):
      """Called at the beginning of training.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_train_end(self, logs=None):
      """Called at the end of training.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently the output of the last call to `on_epoch_end()`
            is passed to this argument for this method but that may change in
            the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_test_begin(self, logs=None):
      """Called at the beginning of evaluation or validation.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_test_end(self, logs=None):
      """Called at the end of evaluation or validation.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently the output of the last call to
            `on_test_batch_end()` is passed to this argument for this method
            but that may change in the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_predict_begin(self, logs=None):
      """Called at the beginning of prediction.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
  
    @doc_controls.for_subclass_implementers
    def on_predict_end(self, logs=None):
      """Called at the end of prediction.
  
      Subclasses should override for any actions to run.
  
      Args:
          logs: Dict. Currently no data is passed to this argument for this method
            but that may change in the future.
      """
  
    def _implements_train_batch_hooks(self):
      """Determines if this Callback should be called for each train batch."""
      return (not generic_utils.is_default(self.on_batch_begin) or
              not generic_utils.is_default(self.on_batch_end) or
              not generic_utils.is_default(self.on_train_batch_begin) or
              not generic_utils.is_default(self.on_train_batch_end))
  
    def _implements_test_batch_hooks(self):
      """Determines if this Callback should be called for each test batch."""
      return (not generic_utils.is_default(self.on_test_batch_begin) or
              not generic_utils.is_default(self.on_test_batch_end))
  
    def _implements_predict_batch_hooks(self):
      """Determines if this Callback should be called for each predict batch."""
      return (not generic_utils.is_default(self.on_predict_batch_begin) or
              not generic_utils.is_default(self.on_predict_batch_end))
  
  
  @keras_export('keras.callbacks.BaseLogger')
  class BaseLogger(Callback):
    """Callback that accumulates epoch averages of metrics.
  
    This callback is automatically applied to every Keras model.
  
    Args:
        stateful_metrics: Iterable of string names of metrics that
            should *not* be averaged over an epoch.
            Metrics in this list will be logged as-is in `on_epoch_end`.
            All others will be averaged in `on_epoch_end`.
    """
  
    def __init__(self, stateful_metrics=None):
      super(BaseLogger, self).__init__()
      self.stateful_metrics = set(stateful_metrics or [])
  
    def on_epoch_begin(self, epoch, logs=None):
      self.seen = 0
      self.totals = {}
  
    def on_batch_end(self, batch, logs=None):
      logs = logs or {}
      batch_size = logs.get('size', 0)
      # In case of distribution strategy we can potentially run multiple steps
      # at the same time, we should account for that in the `seen` calculation.
      num_steps = logs.get('num_steps', 1)
      self.seen += batch_size * num_steps
  
      for k, v in logs.items():
        if k in self.stateful_metrics:
          self.totals[k] = v
        else:
          if k in self.totals:
            self.totals[k] += v * batch_size
          else:
            self.totals[k] = v * batch_size
  
    def on_epoch_end(self, epoch, logs=None):
      if logs is not None:
        for k in self.params['metrics']:
          if k in self.totals:
            # Make value available to next callbacks.
            if k in self.stateful_metrics:
              logs[k] = self.totals[k]
            else:
              logs[k] = self.totals[k] / self.seen
  
  
  @keras_export('keras.callbacks.TerminateOnNaN')
  class TerminateOnNaN(Callback):
    """Callback that terminates training when a NaN loss is encountered.
    """
  
    def __init__(self):
      super(TerminateOnNaN, self).__init__()
      self._supports_tf_logs = True
  
    def on_batch_end(self, batch, logs=None):
      logs = logs or {}
      loss = logs.get('loss')
      if loss is not None:
        loss = tf_utils.to_numpy_or_python_type(loss)
        if np.isnan(loss) or np.isinf(loss):
          print('Batch %d: Invalid loss, terminating training' % (batch))
          self.model.stop_training = True
  
  
  @keras_export('keras.callbacks.ProgbarLogger')
  class ProgbarLogger(Callback):
    """Callback that prints metrics to stdout.
  
    Args:
        count_mode: One of `"steps"` or `"samples"`.
            Whether the progress bar should
            count samples seen or steps (batches) seen.
        stateful_metrics: Iterable of string names of metrics that
            should *not* be averaged over an epoch.
            Metrics in this list will be logged as-is.
            All others will be averaged over time (e.g. loss, etc).
            If not provided, defaults to the `Model`'s metrics.
  
    Raises:
        ValueError: In case of invalid `count_mode`.
    """
  
    def __init__(self, count_mode='samples', stateful_metrics=None):
      super(ProgbarLogger, self).__init__()
      self._supports_tf_logs = True
      if count_mode == 'samples':
        self.use_steps = False
      elif count_mode == 'steps':
        self.use_steps = True
      else:
        raise ValueError('Unknown `count_mode`: ' + str(count_mode))
      # Defaults to all Model's metrics except for loss.
      self.stateful_metrics = set(stateful_metrics) if stateful_metrics else None
  
      self.seen = 0
      self.progbar = None
      self.target = None
      self.verbose = 1
      self.epochs = 1
  
      self._train_step, self._test_step, self._predict_step = None, None, None
      self._call_batch_hooks = True
  
      self._called_in_fit = False
  
    def set_params(self, params):
      self.verbose = params['verbose']
      self.epochs = params['epochs']
      if self.use_steps and 'steps' in params:
        self.target = params['steps']
      elif not self.use_steps and 'samples' in params:
        self.target = params['samples']
      else:
        self.target = None  # Will be inferred at the end of the first epoch.
  
      self._call_batch_hooks = self.verbose == 1
      if self.target is None:
        try:
          self._train_step = self.model._train_counter  # pylint: disable=protected-access
          self._test_step = self.model._test_counter  # pylint: disable=protected-access
          self._predict_step = self.model._predict_counter  # pylint: disable=protected-access
        except AttributeError:
          self._call_batch_hooks = True
  
    def on_train_begin(self, logs=None):
      # When this logger is called inside `fit`, validation is silent.
      self._called_in_fit = True
  
    def on_test_begin(self, logs=None):
      if not self._called_in_fit:
        self._reset_progbar()
        self._maybe_init_progbar()
  
    def on_predict_begin(self, logs=None):
      self._reset_progbar()
      self._maybe_init_progbar()
  
    def on_epoch_begin(self, epoch, logs=None):
      self._reset_progbar()
      self._maybe_init_progbar()
      if self.verbose and self.epochs > 1:
        print('Epoch %d/%d' % (epoch + 1, self.epochs))
  
    def on_train_batch_end(self, batch, logs=None):
      self._batch_update_progbar(batch, logs)
  
    def on_test_batch_end(self, batch, logs=None):
      if not self._called_in_fit:
        self._batch_update_progbar(batch, logs)
  
    def on_predict_batch_end(self, batch, logs=None):
      # Don't pass prediction results.
      self._batch_update_progbar(batch, None)
  
    def on_epoch_end(self, epoch, logs=None):
      self._finalize_progbar(logs, self._train_step)
  
    def on_test_end(self, logs=None):
      if not self._called_in_fit:
        self._finalize_progbar(logs, self._test_step)
  
    def on_predict_end(self, logs=None):
      self._finalize_progbar(logs, self._predict_step)
  
    def _reset_progbar(self):
      self.seen = 0
      self.progbar = None
  
    def _maybe_init_progbar(self):
      if self.stateful_metrics is None:
        if self.model:
          self.stateful_metrics = set(m.name for m in self.model.metrics)
        else:
          self.stateful_metrics = set()
  
      if self.progbar is None:
        self.progbar = Progbar(
            target=self.target,
            verbose=self.verbose,
            stateful_metrics=self.stateful_metrics,
            unit_name='step' if self.use_steps else 'sample')
  
    def _implements_train_batch_hooks(self):
      return self._call_batch_hooks
  
    def _implements_test_batch_hooks(self):
      return self._call_batch_hooks
  
    def _implements_predict_batch_hooks(self):
      return self._call_batch_hooks
  
    def _batch_update_progbar(self, batch, logs=None):
      """Updates the progbar."""
      logs = logs or {}
      self._maybe_init_progbar()
      if self.use_steps:
        self.seen = batch + 1  # One-indexed.
      else:
        # v1 path only.
        logs = copy.copy(logs)
        batch_size = logs.pop('size', 0)
        num_steps = logs.pop('num_steps', 1)
        logs.pop('batch', None)
        add_seen = num_steps * batch_size
        self.seen += add_seen
  
      if self.verbose == 1:
        # Only block async when verbose = 1.
        logs = tf_utils.to_numpy_or_python_type(logs)
        self.progbar.update(self.seen, list(logs.items()), finalize=False)
  
    def _finalize_progbar(self, logs, counter):
      logs = tf_utils.to_numpy_or_python_type(logs or {})
      if self.target is None:
        if counter is not None:
          counter = counter.numpy()
          if not self.use_steps:
            counter *= logs.get('size', 1)
        self.target = counter or self.seen
        self.progbar.target = self.target
      self.progbar.update(self.target, list(logs.items()), finalize=True)
  
  
  @keras_export('keras.callbacks.History')
  class History(Callback):
    """Callback that records events into a `History` object.
  
    This callback is automatically applied to
    every Keras model. The `History` object
    gets returned by the `fit` method of models.
    """
  
    def __init__(self):
      super(History, self).__init__()
      self.history = {}
  
    def on_train_begin(self, logs=None):
      self.epoch = []
  
    def on_epoch_end(self, epoch, logs=None):
      logs = logs or {}
      self.epoch.append(epoch)
      for k, v in logs.items():
        self.history.setdefault(k, []).append(v)
  
      # Set the history attribute on the model after the epoch ends. This will
      # make sure that the state which is set is the latest one.
      self.model.history = self
  
  
  @keras_export('keras.callbacks.ModelCheckpoint')
  class ModelCheckpoint(Callback):
    """Callback to save the Keras model or model weights at some frequency.
  
    `ModelCheckpoint` callback is used in conjunction with training using
    `model.fit()` to save a model or weights (in a checkpoint file) at some
    interval, so the model or weights can be loaded later to continue the training
    from the state saved.
  
    A few options this callback provides include:
  
    - Whether to only keep the model that has achieved the "best performance" so
      far, or whether to save the model at the end of every epoch regardless of
      performance.
    - Definition of 'best'; which quantity to monitor and whether it should be
      maximized or minimized.
    - The frequency it should save at. Currently, the callback supports saving at
      the end of every epoch, or after a fixed number of training batches.
    - Whether only weights are saved, or the whole model is saved.
  
    Note: If you get `WARNING:tensorflow:Can save best model only with <name>
    available, skipping` see the description of the `monitor` argument for
    details on how to get this right.
  
    Example:
  
    ```python
    model.compile(loss=..., optimizer=...,
                  metrics=['accuracy'])
  
    EPOCHS = 10
    checkpoint_filepath = '/tmp/checkpoint'
    model_checkpoint_callback = tf.keras.callbacks.ModelCheckpoint(
        filepath=checkpoint_filepath,
        save_weights_only=True,
        monitor='val_accuracy',
        mode='max',
        save_best_only=True)
  
    # Model weights are saved at the end of every epoch, if it's the best seen
    # so far.
    model.fit(epochs=EPOCHS, callbacks=[model_checkpoint_callback])
  
    # The model weights (that are considered the best) are loaded into the model.
    model.load_weights(checkpoint_filepath)
    ```
  
    Args:
        filepath: string or `PathLike`, path to save the model file. e.g.
          filepath = os.path.join(working_dir, 'ckpt', file_name). `filepath`
          can contain named formatting options, which will be filled the value of
          `epoch` and keys in `logs` (passed in `on_epoch_end`). For example: if
          `filepath` is `weights.{epoch:02d}-{val_loss:.2f}.hdf5`, then the model
          checkpoints will be saved with the epoch number and the validation loss
          in the filename. The directory of the filepath should not be reused by
          any other callbacks to avoid conflicts.
        monitor: The metric name to monitor. Typically the metrics are set by the
          `Model.compile` method. Note:
  
          * Prefix the name with `"val_`" to monitor validation metrics.
          * Use `"loss"` or "`val_loss`" to monitor the model's total loss.
          * If you specify metrics as strings, like `"accuracy"`, pass the same
            string (with or without the `"val_"` prefix).
          * If you pass `metrics.Metric` objects, `monitor` should be set to
            `metric.name`
          * If you're not sure about the metric names you can check the contents
            of the `history.history` dictionary returned by
            `history = model.fit()`
          * Multi-output models set additional prefixes on the metric names.
  
        verbose: verbosity mode, 0 or 1.
        save_best_only: if `save_best_only=True`, it only saves when the model
          is considered the "best" and the latest best model according to the
          quantity monitored will not be overwritten. If `filepath` doesn't
          contain formatting options like `{epoch}` then `filepath` will be
          overwritten by each new better model.
        mode: one of {'auto', 'min', 'max'}. If `save_best_only=True`, the
          decision to overwrite the current save file is made based on either
          the maximization or the minimization of the monitored quantity.
          For `val_acc`, this should be `max`, for `val_loss` this should be
          `min`, etc. In `auto` mode, the direction is automatically inferred
          from the name of the monitored quantity.
        save_weights_only: if True, then only the model's weights will be saved
          (`model.save_weights(filepath)`), else the full model is saved
          (`model.save(filepath)`).
        save_freq: `'epoch'` or integer. When using `'epoch'`, the callback saves
          the model after each epoch. When using integer, the callback saves the
          model at end of this many batches. If the `Model` is compiled with
          `steps_per_execution=N`, then the saving criteria will be
          checked every Nth batch. Note that if the saving isn't aligned to
          epochs, the monitored metric may potentially be less reliable (it
          could reflect as little as 1 batch, since the metrics get reset every
          epoch). Defaults to `'epoch'`.
        options: Optional `tf.train.CheckpointOptions` object if
          `save_weights_only` is true or optional `tf.saved_model.SaveOptions`
          object if `save_weights_only` is false.
        **kwargs: Additional arguments for backwards compatibility. Possible key
          is `period`.
    """
  
    def __init__(self,
                 filepath,
                 monitor='val_loss',
                 verbose=0,
                 save_best_only=False,
                 save_weights_only=False,
                 mode='auto',
                 save_freq='epoch',
                 options=None,
                 **kwargs):
      super(ModelCheckpoint, self).__init__()
      self._supports_tf_logs = True
      self.monitor = monitor
      self.verbose = verbose
      self.filepath = path_to_string(filepath)
      self.save_best_only = save_best_only
      self.save_weights_only = save_weights_only
      self.save_freq = save_freq
      self.epochs_since_last_save = 0
      self._batches_seen_since_last_saving = 0
      self._last_batch_seen = 0
  
      if save_weights_only:
        if options is None or isinstance(
            options, tf.train.CheckpointOptions):
          self._options = options or tf.train.CheckpointOptions()
        else:
          raise TypeError('If save_weights_only is True, then `options` must be'
                          'either None or a tf.train.CheckpointOptions')
      else:
        if options is None or isinstance(options, tf.saved_model.SaveOptions):
          self._options = options or tf.saved_model.SaveOptions()
        else:
          raise TypeError('If save_weights_only is False, then `options` must be'
                          'either None or a tf.saved_model.SaveOptions')
  
      # Deprecated field `load_weights_on_restart` is for loading the checkpoint
      # file from `filepath` at the start of `model.fit()`
      # TODO(rchao): Remove the arg during next breaking release.
      if 'load_weights_on_restart' in kwargs:
        self.load_weights_on_restart = kwargs['load_weights_on_restart']
        logging.warning('`load_weights_on_restart` argument is deprecated. '
                        'Please use `model.load_weights()` for loading weights '
                        'before the start of `model.fit()`.')
      else:
        self.load_weights_on_restart = False
  
      # Deprecated field `period` is for the number of epochs between which
      # the model is saved.
      if 'period' in kwargs:
        self.period = kwargs['period']
        logging.warning('`period` argument is deprecated. Please use `save_freq` '
                        'to specify the frequency in number of batches seen.')
      else:
        self.period = 1
  
      if mode not in ['auto', 'min', 'max']:
        logging.warning('ModelCheckpoint mode %s is unknown, '
                        'fallback to auto mode.', mode)
        mode = 'auto'
  
      if mode == 'min':
        self.monitor_op = np.less
        self.best = np.Inf
      elif mode == 'max':
        self.monitor_op = np.greater
        self.best = -np.Inf
      else:
        if 'acc' in self.monitor or self.monitor.startswith('fmeasure'):
          self.monitor_op = np.greater
          self.best = -np.Inf
        else:
          self.monitor_op = np.less
          self.best = np.Inf
  
      if self.save_freq != 'epoch' and not isinstance(self.save_freq, int):
        raise ValueError('Unrecognized save_freq: {}'.format(self.save_freq))
  
      # Only the chief worker writes model checkpoints, but all workers
      # restore checkpoint at on_train_begin().
      self._chief_worker_only = False
  
    def set_model(self, model):
      self.model = model
      # Use name matching rather than `isinstance` to avoid circular dependencies.
      if (not self.save_weights_only and
          not model._is_graph_network and  # pylint: disable=protected-access
          model.__class__.__name__ != 'Sequential'):
        self.save_weights_only = True
  
    def on_train_begin(self, logs=None):
      if self.load_weights_on_restart:
        filepath_to_load = (
            self._get_most_recently_modified_file_matching_pattern(self.filepath))
        if (filepath_to_load is not None and
            self._checkpoint_exists(filepath_to_load)):
          try:
            # `filepath` may contain placeholders such as `{epoch:02d}`, and
            # thus it attempts to load the most recently modified file with file
            # name matching the pattern.
            self.model.load_weights(filepath_to_load)
          except (IOError, ValueError) as e:
            raise ValueError('Error loading file from {}. Reason: {}'.format(
                filepath_to_load, e))
  
    def _implements_train_batch_hooks(self):
      # Only call batch hooks when saving on batch
      return self.save_freq != 'epoch'
  
    def on_train_batch_end(self, batch, logs=None):
      if self._should_save_on_batch(batch):
        self._save_model(epoch=self._current_epoch, logs=logs)
  
    def on_epoch_begin(self, epoch, logs=None):
      self._current_epoch = epoch
  
    def on_epoch_end(self, epoch, logs=None):
      self.epochs_since_last_save += 1
      # pylint: disable=protected-access
      if self.save_freq == 'epoch':
        self._save_model(epoch=epoch, logs=logs)
  
    def _should_save_on_batch(self, batch):
      """Handles batch-level saving logic, supports steps_per_execution."""
      if self.save_freq == 'epoch':
        return False
  
      if batch <= self._last_batch_seen:  # New epoch.
        add_batches = batch + 1  # batches are zero-indexed.
      else:
        add_batches = batch - self._last_batch_seen
      self._batches_seen_since_last_saving += add_batches
      self._last_batch_seen = batch
  
      if self._batches_seen_since_last_saving >= self.save_freq:
        self._batches_seen_since_last_saving = 0
        return True
      return False
  
    def _save_model(self, epoch, logs):
      """Saves the model.
  
      Args:
          epoch: the epoch this iteration is in.
          logs: the `logs` dict passed in to `on_batch_end` or `on_epoch_end`.
      """
      logs = logs or {}
  
      if isinstance(self.save_freq,
                    int) or self.epochs_since_last_save >= self.period:
        # Block only when saving interval is reached.
        logs = tf_utils.to_numpy_or_python_type(logs)
        self.epochs_since_last_save = 0
        filepath = self._get_file_path(epoch, logs)
  
        try:
          if self.save_best_only:
            current = logs.get(self.monitor)
            if current is None:
              logging.warning('Can save best model only with %s available, '
                              'skipping.', self.monitor)
            else:
              if self.monitor_op(current, self.best):
                if self.verbose > 0:
                  print('\nEpoch %05d: %s improved from %0.5f to %0.5f,'
                        ' saving model to %s' % (epoch + 1, self.monitor,
                                                 self.best, current, filepath))
                self.best = current
                if self.save_weights_only:
                  self.model.save_weights(
                      filepath, overwrite=True, options=self._options)
                else:
                  self.model.save(filepath, overwrite=True, options=self._options)
              else:
                if self.verbose > 0:
                  print('\nEpoch %05d: %s did not improve from %0.5f' %
                        (epoch + 1, self.monitor, self.best))
          else:
            if self.verbose > 0:
              print('\nEpoch %05d: saving model to %s' % (epoch + 1, filepath))
            if self.save_weights_only:
              self.model.save_weights(
                  filepath, overwrite=True, options=self._options)
            else:
              self.model.save(filepath, overwrite=True, options=self._options)
  
          self._maybe_remove_file()
        except IOError as e:
          # `e.errno` appears to be `None` so checking the content of `e.args[0]`.
          if 'is a directory' in six.ensure_str(e.args[0]).lower():
            raise IOError('Please specify a non-directory filepath for '
                          'ModelCheckpoint. Filepath used is an existing '
                          'directory: {}'.format(filepath))
          # Re-throw the error for any other causes.
          raise e
  
    def _get_file_path(self, epoch, logs):
      """Returns the file path for checkpoint."""
      # pylint: disable=protected-access
      try:
        # `filepath` may contain placeholders such as `{epoch:02d}` and
        # `{mape:.2f}`. A mismatch between logged metrics and the path's
        # placeholders can cause formatting to fail.
        file_path = self.filepath.format(epoch=epoch + 1, **logs)
      except KeyError as e:
        raise KeyError('Failed to format this callback filepath: "{}". '
                       'Reason: {}'.format(self.filepath, e))
      self._write_filepath = distributed_file_utils.write_filepath(
          file_path, self.model.distribute_strategy)
      return self._write_filepath
  
    def _maybe_remove_file(self):
      # Remove the checkpoint directory in multi-worker training where this worker
      # should not checkpoint. It is a dummy directory previously saved for sync
      # distributed training.
      distributed_file_utils.remove_temp_dir_with_filepath(
          self._write_filepath, self.model.distribute_strategy)
  
    def _checkpoint_exists(self, filepath):
      """Returns whether the checkpoint `filepath` refers to exists."""
      if filepath.endswith('.h5'):
        return tf.io.gfile.exists(filepath)
      tf_saved_model_exists = tf.io.gfile.exists(filepath)
      tf_weights_only_checkpoint_exists = tf.io.gfile.exists(
          filepath + '.index')
      return tf_saved_model_exists or tf_weights_only_checkpoint_exists
  
    def _get_most_recently_modified_file_matching_pattern(self, pattern):
      """Returns the most recently modified filepath matching pattern.
  
      Pattern may contain python formatting placeholder. If
      `tf.train.latest_checkpoint()` does not return None, use that; otherwise,
      check for most recently modified one that matches the pattern.
  
      In the rare case where there are more than one pattern-matching file having
      the same modified time that is most recent among all, return the filepath
      that is largest (by `>` operator, lexicographically using the numeric
      equivalents). This provides a tie-breaker when multiple files are most
      recent. Note that a larger `filepath` can sometimes indicate a later time of
      modification (for instance, when epoch/batch is used as formatting option),
      but not necessarily (when accuracy or loss is used). The tie-breaker is
      put in the logic as best effort to return the most recent, and to avoid
      undeterministic result.
  
      Modified time of a file is obtained with `os.path.getmtime()`.
  
      This utility function is best demonstrated via an example:
  
      ```python
      file_pattern = 'f.batch{batch:02d}epoch{epoch:02d}.h5'
      test_dir = self.get_temp_dir()
      path_pattern = os.path.join(test_dir, file_pattern)
      file_paths = [
          os.path.join(test_dir, file_name) for file_name in
          ['f.batch03epoch02.h5', 'f.batch02epoch02.h5', 'f.batch01epoch01.h5']
      ]
      for file_path in file_paths:
        # Write something to each of the files
      self.assertEqual(
          _get_most_recently_modified_file_matching_pattern(path_pattern),
          file_paths[-1])
      ```
  
      Args:
          pattern: The file pattern that may optionally contain python placeholder
              such as `{epoch:02d}`.
  
      Returns:
          The most recently modified file's full filepath matching `pattern`. If
          `pattern` does not contain any placeholder, this returns the filepath
          that
          exactly matches `pattern`. Returns `None` if no match is found.
      """
      dir_name = os.path.dirname(pattern)
      base_name = os.path.basename(pattern)
      base_name_regex = '^' + re.sub(r'{.*}', r'.*', base_name) + '$'
  
      # If tf.train.latest_checkpoint tells us there exists a latest checkpoint,
      # use that as it is more robust than `os.path.getmtime()`.
      latest_tf_checkpoint = tf.train.latest_checkpoint(dir_name)
      if latest_tf_checkpoint is not None and re.match(
          base_name_regex, os.path.basename(latest_tf_checkpoint)):
        return latest_tf_checkpoint
  
      latest_mod_time = 0
      file_path_with_latest_mod_time = None
      n_file_with_latest_mod_time = 0
      file_path_with_largest_file_name = None
  
      if tf.io.gfile.exists(dir_name):
        for file_name in os.listdir(dir_name):
          # Only consider if `file_name` matches the pattern.
          if re.match(base_name_regex, file_name):
            file_path = os.path.join(dir_name, file_name)
            mod_time = os.path.getmtime(file_path)
            if (file_path_with_largest_file_name is None or
                file_path > file_path_with_largest_file_name):
              file_path_with_largest_file_name = file_path
            if mod_time > latest_mod_time:
              latest_mod_time = mod_time
              file_path_with_latest_mod_time = file_path
              # In the case a file with later modified time is found, reset
              # the counter for the number of files with latest modified time.
              n_file_with_latest_mod_time = 1
            elif mod_time == latest_mod_time:
              # In the case a file has modified time tied with the most recent,
              # increment the counter for the number of files with latest modified
              # time by 1.
              n_file_with_latest_mod_time += 1
  
      if n_file_with_latest_mod_time == 1:
        # Return the sole file that has most recent modified time.
        return file_path_with_latest_mod_time
      else:
        # If there are more than one file having latest modified time, return
        # the file path with the largest file name.
        return file_path_with_largest_file_name
  
  
  @keras_export('keras.callbacks.experimental.BackupAndRestore', v1=[])
  class BackupAndRestore(Callback):
    """Callback to back up and restore the training state.
  
    `BackupAndRestore` callback is intended to recover from interruptions that
    happened in the middle of a model.fit execution by backing up the
    training states in a temporary checkpoint file (based on TF CheckpointManager)
    at the end of each epoch. If training restarted before completion, the
    training state and model are restored to the most recently saved state at the
    beginning of a new model.fit() run.
    Note that user is responsible to bring jobs back up.
    This callback is important for the backup and restore mechanism for fault
    tolerance purpose. And the model to be restored from an previous checkpoint is
    expected to be the same as the one used to back up. If user changes arguments
    passed to compile or fit, the checkpoint saved for fault tolerance can become
    invalid.
  
    Note:
    1. This callback is not compatible with disabling eager execution.
    2. A checkpoint is saved at the end of each epoch, when restoring we'll redo
    any partial work from an unfinished epoch in which the training got restarted
    (so the work done before a interruption doesn't affect the final model state).
    3. This works for both single worker and multi-worker mode, only
    MirroredStrategy and MultiWorkerMirroredStrategy are supported for now.
  
    Example:
  
    >>> class InterruptingCallback(tf.keras.callbacks.Callback):
    ...   def on_epoch_begin(self, epoch, logs=None):
    ...     if epoch == 4:
    ...       raise RuntimeError('Interrupting!')
    >>> callback = tf.keras.callbacks.experimental.BackupAndRestore(
    ... backup_dir="/tmp/backup")
    >>> model = tf.keras.models.Sequential([tf.keras.layers.Dense(10)])
    >>> model.compile(tf.keras.optimizers.SGD(), loss='mse')
    >>> try:
    ...   model.fit(np.arange(100).reshape(5, 20), np.zeros(5), epochs=10,
    ...             batch_size=1, callbacks=[callback, InterruptingCallback()],
    ...             verbose=0)
    ... except:
    ...   pass
    >>> history = model.fit(np.arange(100).reshape(5, 20), np.zeros(5), epochs=10,
    ...             batch_size=1, callbacks=[callback], verbose=0)
    >>> # Only 6 more epochs are run, since first trainning got interrupted at
    >>> # zero-indexed epoch 4, second training will continue from 4 to 9.
    >>> len(history.history['loss'])
    6
  
    Args:
        backup_dir: String, path to store the checkpoint.
          e.g. backup_dir = os.path.join(working_dir, 'backup')
          This is the directory in which the system stores temporary files to
          recover the model from jobs terminated unexpectedly. The directory
          cannot be reused elsewhere to store other files, e.g. by
          BackupAndRestore callback of another training, or by another callback
          (ModelCheckpoint) of the same training.
    """
  
    def __init__(self, backup_dir):
      super(BackupAndRestore, self).__init__()
      self.backup_dir = backup_dir
      self._supports_tf_logs = True
      self._supported_strategies = (
          tf.distribute.MirroredStrategy,
          tf.distribute.MultiWorkerMirroredStrategy,
          tf.distribute.experimental.TPUStrategy, tf.distribute.TPUStrategy)
  
      if not tf.executing_eagerly():
        if tf.inside_function():
          raise ValueError('This Callback\'s method contains Python state and '
                           'should be called outside of `tf.function`s.')
        else:  # Legacy graph mode:
          raise ValueError(
              'BackupAndRestore only supports eager mode. In graph '
              'mode, consider using ModelCheckpoint to manually save '
              'and restore weights with `model.load_weights()` and by '
              'providing `initial_epoch` in `model.fit()` for fault tolerance.')
  
      # Only the chief worker writes model checkpoints, but all workers
      # restore checkpoint at on_train_begin().
      self._chief_worker_only = False
  
    def set_model(self, model):
      self.model = model
  
    def on_train_begin(self, logs=None):
      # TrainingState is used to manage the training state needed for
      # failure-recovery of a worker in training.
      # pylint: disable=protected-access
  
      if self.model._distribution_strategy and not isinstance(
          self.model.distribute_strategy, self._supported_strategies):
        raise NotImplementedError(
            '%s is not supported yet. '
            'Currently BackupAndRestore callback only supports empty strategy, '
            'MirroredStrategy, MultiWorkerMirroredStrategy and TPUStrategy.' %
            type(self.model.distribute_strategy).__name__)
      self.model._training_state = (
          worker_training_state.WorkerTrainingState(self.model, self.backup_dir))
      self._training_state = self.model._training_state
      self._training_state.restore()
  
    def on_train_end(self, logs=None):
      # pylint: disable=protected-access
      # On exit of training, delete the training state backup file that was saved
      # for the purpose of worker recovery.
      self._training_state.delete_backup()
  
      # Clean up the training state.
      del self._training_state
      del self.model._training_state
  
    def on_epoch_end(self, epoch, logs=None):
      # Back up the model and current epoch for possible future recovery.
      self._training_state.back_up(epoch)
  
  
  @keras_export('keras.callbacks.EarlyStopping')
  class EarlyStopping(Callback):
    """Stop training when a monitored metric has stopped improving.
  
    Assuming the goal of a training is to minimize the loss. With this, the
    metric to be monitored would be `'loss'`, and mode would be `'min'`. A
    `model.fit()` training loop will check at end of every epoch whether
    the loss is no longer decreasing, considering the `min_delta` and
    `patience` if applicable. Once it's found no longer decreasing,
    `model.stop_training` is marked True and the training terminates.
  
    The quantity to be monitored needs to be available in `logs` dict.
    To make it so, pass the loss or metrics at `model.compile()`.
  
    Args:
      monitor: Quantity to be monitored.
      min_delta: Minimum change in the monitored quantity
          to qualify as an improvement, i.e. an absolute
          change of less than min_delta, will count as no
          improvement.
      patience: Number of epochs with no improvement
          after which training will be stopped.
      verbose: verbosity mode.
      mode: One of `{"auto", "min", "max"}`. In `min` mode,
          training will stop when the quantity
          monitored has stopped decreasing; in `"max"`
          mode it will stop when the quantity
          monitored has stopped increasing; in `"auto"`
          mode, the direction is automatically inferred
          from the name of the monitored quantity.
      baseline: Baseline value for the monitored quantity.
          Training will stop if the model doesn't show improvement over the
          baseline.
      restore_best_weights: Whether to restore model weights from
          the epoch with the best value of the monitored quantity.
          If False, the model weights obtained at the last step of
          training are used.
  
    Example:
  
    >>> callback = tf.keras.callbacks.EarlyStopping(monitor='loss', patience=3)
    >>> # This callback will stop the training when there is no improvement in
    >>> # the loss for three consecutive epochs.
    >>> model = tf.keras.models.Sequential([tf.keras.layers.Dense(10)])
    >>> model.compile(tf.keras.optimizers.SGD(), loss='mse')
    >>> history = model.fit(np.arange(100).reshape(5, 20), np.zeros(5),
    ...                     epochs=10, batch_size=1, callbacks=[callback],
    ...                     verbose=0)
    >>> len(history.history['loss'])  # Only 4 epochs are run.
    4
    """
  
    def __init__(self,
                 monitor='val_loss',
                 min_delta=0,
                 patience=0,
                 verbose=0,
                 mode='auto',
                 baseline=None,
                 restore_best_weights=False):
      super(EarlyStopping, self).__init__()
  
      self.monitor = monitor
      self.patience = patience
      self.verbose = verbose
      self.baseline = baseline
      self.min_delta = abs(min_delta)
      self.wait = 0
      self.stopped_epoch = 0
      self.restore_best_weights = restore_best_weights
      self.best_weights = None
  
      if mode not in ['auto', 'min', 'max']:
        logging.warning('EarlyStopping mode %s is unknown, '
                        'fallback to auto mode.', mode)
        mode = 'auto'
  
      if mode == 'min':
        self.monitor_op = np.less
      elif mode == 'max':
        self.monitor_op = np.greater
      else:
        if 'acc' in self.monitor:
          self.monitor_op = np.greater
        else:
          self.monitor_op = np.less
  
      if self.monitor_op == np.greater:
        self.min_delta *= 1
      else:
        self.min_delta *= -1
  
    def on_train_begin(self, logs=None):
      # Allow instances to be re-used
      self.wait = 0
      self.stopped_epoch = 0
      if self.baseline is not None:
        self.best = self.baseline
      else:
        self.best = np.Inf if self.monitor_op == np.less else -np.Inf
      self.best_weights = None
  
    def on_epoch_end(self, epoch, logs=None):
      current = self.get_monitor_value(logs)
      if current is None:
        return
      if self.monitor_op(current - self.min_delta, self.best):
        self.best = current
        self.wait = 0
        if self.restore_best_weights:
          self.best_weights = self.model.get_weights()
      else:
        self.wait += 1
        if self.wait >= self.patience:
          self.stopped_epoch = epoch
          self.model.stop_training = True
          if self.restore_best_weights:
            if self.verbose > 0:
              print('Restoring model weights from the end of the best epoch.')
            self.model.set_weights(self.best_weights)
  
    def on_train_end(self, logs=None):
      if self.stopped_epoch > 0 and self.verbose > 0:
        print('Epoch %05d: early stopping' % (self.stopped_epoch + 1))
  
    def get_monitor_value(self, logs):
      logs = logs or {}
      monitor_value = logs.get(self.monitor)
      if monitor_value is None:
        logging.warning('Early stopping conditioned on metric `%s` '
                        'which is not available. Available metrics are: %s',
                        self.monitor, ','.join(list(logs.keys())))
      return monitor_value
  
  
  @keras_export('keras.callbacks.RemoteMonitor')
  class RemoteMonitor(Callback):
    """Callback used to stream events to a server.
  
    Requires the `requests` library.
    Events are sent to `root + '/publish/epoch/end/'` by default. Calls are
    HTTP POST, with a `data` argument which is a
    JSON-encoded dictionary of event data.
    If `send_as_json=True`, the content type of the request will be
    `"application/json"`.
    Otherwise the serialized JSON will be sent within a form.
  
    Args:
      root: String; root url of the target server.
      path: String; path relative to `root` to which the events will be sent.
      field: String; JSON field under which the data will be stored.
          The field is used only if the payload is sent within a form
          (i.e. send_as_json is set to False).
      headers: Dictionary; optional custom HTTP headers.
      send_as_json: Boolean; whether the request should be
          sent as `"application/json"`.
    """
  
    def __init__(self,
                 root='http://localhost:9000',
                 path='/publish/epoch/end/',
                 field='data',
                 headers=None,
                 send_as_json=False):
      super(RemoteMonitor, self).__init__()
  
      self.root = root
      self.path = path
      self.field = field
      self.headers = headers
      self.send_as_json = send_as_json
  
    def on_epoch_end(self, epoch, logs=None):
      if requests is None:
        raise ImportError('RemoteMonitor requires the `requests` library.')
      logs = logs or {}
      send = {}
      send['epoch'] = epoch
      for k, v in logs.items():
        # np.ndarray and np.generic are not scalar types
        # therefore we must unwrap their scalar values and
        # pass to the json-serializable dict 'send'
        if isinstance(v, (np.ndarray, np.generic)):
          send[k] = v.item()
        else:
          send[k] = v
      try:
        if self.send_as_json:
          requests.post(self.root + self.path, json=send, headers=self.headers)
        else:
          requests.post(
              self.root + self.path, {self.field: json.dumps(send)},
              headers=self.headers)
      except requests.exceptions.RequestException:
        logging.warning('Warning: could not reach RemoteMonitor '
                        'root server at ' + str(self.root))
  
  
  @keras_export('keras.callbacks.LearningRateScheduler')
  class LearningRateScheduler(Callback):
    """Learning rate scheduler.
  
    At the beginning of every epoch, this callback gets the updated learning rate
    value from `schedule` function provided at `__init__`, with the current epoch
    and current learning rate, and applies the updated learning rate
    on the optimizer.
  
    Args:
      schedule: a function that takes an epoch index (integer, indexed from 0)
          and current learning rate (float) as inputs and returns a new
          learning rate as output (float).
      verbose: int. 0: quiet, 1: update messages.
  
    Example:
  
    >>> # This function keeps the initial learning rate for the first ten epochs
    >>> # and decreases it exponentially after that.
    >>> def scheduler(epoch, lr):
    ...   if epoch < 10:
    ...     return lr
    ...   else:
    ...     return lr * tf.math.exp(-0.1)
    >>>
    >>> model = tf.keras.models.Sequential([tf.keras.layers.Dense(10)])
    >>> model.compile(tf.keras.optimizers.SGD(), loss='mse')
    >>> round(model.optimizer.lr.numpy(), 5)
    0.01
  
    >>> callback = tf.keras.callbacks.LearningRateScheduler(scheduler)
    >>> history = model.fit(np.arange(100).reshape(5, 20), np.zeros(5),
    ...                     epochs=15, callbacks=[callback], verbose=0)
    >>> round(model.optimizer.lr.numpy(), 5)
    0.00607
  
    """
  
    def __init__(self, schedule, verbose=0):
      super(LearningRateScheduler, self).__init__()
      self.schedule = schedule
      self.verbose = verbose
  
    def on_epoch_begin(self, epoch, logs=None):
      if not hasattr(self.model.optimizer, 'lr'):
        raise ValueError('Optimizer must have a "lr" attribute.')
      try:  # new API
        lr = float(K.get_value(self.model.optimizer.lr))
        lr = self.schedule(epoch, lr)
      except TypeError:  # Support for old API for backward compatibility
        lr = self.schedule(epoch)
      if not isinstance(lr, (tf.Tensor, float, np.float32, np.float64)):
        raise ValueError('The output of the "schedule" function '
                         'should be float.')
      if isinstance(lr, tf.Tensor) and not lr.dtype.is_floating:
        raise ValueError('The dtype of Tensor should be float')
      K.set_value(self.model.optimizer.lr, K.get_value(lr))
      if self.verbose > 0:
        print('\nEpoch %05d: LearningRateScheduler reducing learning '
              'rate to %s.' % (epoch + 1, lr))
  
    def on_epoch_end(self, epoch, logs=None):
      logs = logs or {}
      logs['lr'] = K.get_value(self.model.optimizer.lr)
  
  
  def keras_model_summary(name, data, step=None):
    """Writes a Keras model as JSON to as a Summary.
  
    Writing the Keras model configuration allows the TensorBoard graph plugin to
    render a conceptual graph, as opposed to graph of ops. In case the model fails
    to serialize as JSON, it ignores and returns False.
  
    Args:
      name: A name for this summary. The summary tag used for TensorBoard will be
        this name prefixed by any active name scopes.
      data: A Keras Model to write.
      step: Explicit `int64`-castable monotonic step value for this summary. If
        omitted, this defaults to `tf.summary.experimental.get_step()`, which must
        not be None.
  
    Returns:
      True on success, or False if no summary was written because no default
      summary writer was available.
  
    Raises:
      ValueError: if a default writer exists, but no step was provided and
        `tf.summary.experimental.get_step()` is None.
    """
    summary_metadata = tf.compat.v1.SummaryMetadata()
    # Hard coding a plugin name. Please refer to go/tb-plugin-name-hardcode for
    # the rationale.
    summary_metadata.plugin_data.plugin_name = 'graph_keras_model'
    # version number = 1
    summary_metadata.plugin_data.content = b'1'
  
    try:
      json_string = data.to_json()
    except Exception as exc:  # pylint: disable=broad-except
      # An exception should not break a model code.
      logging.warn('Model failed to serialize as JSON. Ignoring... %s', exc)
      return False
  
    with tf.summary.experimental.summary_scope(name, 'graph_keras_model',
                                      [data, step]) as (tag, _):
      with tf.compat.v1.device('cpu:0'):
        tensor = tf.constant(json_string, dtype=tf.string)
      return tf.summary.write(
          tag=tag, tensor=tensor, step=step, metadata=summary_metadata)
  
  
  @keras_export('keras.callbacks.TensorBoard', v1=[])
  class TensorBoard(Callback, version_utils.TensorBoardVersionSelector):
    # pylint: disable=line-too-long
    """Enable visualizations for TensorBoard.
  
    TensorBoard is a visualization tool provided with TensorFlow.
  
    This callback logs events for TensorBoard, including:
  
    * Metrics summary plots
    * Training graph visualization
    * Activation histograms
    * Sampled profiling
  
    If you have installed TensorFlow with pip, you should be able
    to launch TensorBoard from the command line:
  
    ```
    tensorboard --logdir=path_to_your_logs
    ```
  
    You can find more information about TensorBoard
    [here](https://www.tensorflow.org/get_started/summaries_and_tensorboard).
  
    Args:
        log_dir: the path of the directory where to save the log files to be
          parsed by TensorBoard. e.g. log_dir = os.path.join(working_dir, 'logs')
          This directory should not be reused by any other callbacks.
        histogram_freq: frequency (in epochs) at which to compute activation and
          weight histograms for the layers of the model. If set to 0, histograms
          won't be computed. Validation data (or split) must be specified for
          histogram visualizations.
        write_graph: whether to visualize the graph in TensorBoard. The log file
          can become quite large when write_graph is set to True.
        write_images: whether to write model weights to visualize as image in
          TensorBoard.
        write_steps_per_second: whether to log the training steps per second into
          Tensorboard. This supports both epoch and batch frequency logging.
        update_freq: `'batch'` or `'epoch'` or integer. When using `'batch'`,
          writes the losses and metrics to TensorBoard after each batch. The same
          applies for `'epoch'`. If using an integer, let's say `1000`, the
          callback will write the metrics and losses to TensorBoard every 1000
          batches. Note that writing too frequently to TensorBoard can slow down
          your training.
        profile_batch: Profile the batch(es) to sample compute characteristics.
          profile_batch must be a non-negative integer or a tuple of integers.
          A pair of positive integers signify a range of batches to profile.
          By default, it will profile the second batch. Set profile_batch=0
          to disable profiling.
        embeddings_freq: frequency (in epochs) at which embedding layers will be
          visualized. If set to 0, embeddings won't be visualized.
        embeddings_metadata: a dictionary which maps layer name to a file name in
          which metadata for this embedding layer is saved. See the
          [details](
            https://www.tensorflow.org/how_tos/embedding_viz/#metadata_optional)
          about metadata files format. In case if the same metadata file is
          used for all embedding layers, string can be passed.
  
    Examples:
  
    Basic usage:
  
    ```python
    tensorboard_callback = tf.keras.callbacks.TensorBoard(log_dir="./logs")
    model.fit(x_train, y_train, epochs=2, callbacks=[tensorboard_callback])
    # Then run the tensorboard command to view the visualizations.
    ```
  
    Custom batch-level summaries in a subclassed Model:
  
    ```python
    class MyModel(tf.keras.Model):
  
      def build(self, _):
        self.dense = tf.keras.layers.Dense(10)
  
      def call(self, x):
        outputs = self.dense(x)
        tf.summary.histogram('outputs', outputs)
        return outputs
  
    model = MyModel()
    model.compile('sgd', 'mse')
  
    # Make sure to set `update_freq=N` to log a batch-level summary every N batches.
    # In addition to any `tf.summary` contained in `Model.call`, metrics added in
    # `Model.compile` will be logged every N batches.
    tb_callback = tf.keras.callbacks.TensorBoard('./logs', update_freq=1)
    model.fit(x_train, y_train, callbacks=[tb_callback])
    ```
  
    Custom batch-level summaries in a Functional API Model:
  
    ```python
    def my_summary(x):
      tf.summary.histogram('x', x)
      return x
  
    inputs = tf.keras.Input(10)
    x = tf.keras.layers.Dense(10)(inputs)
    outputs = tf.keras.layers.Lambda(my_summary)(x)
    model = tf.keras.Model(inputs, outputs)
    model.compile('sgd', 'mse')
  
    # Make sure to set `update_freq=N` to log a batch-level summary every N batches.
    # In addition to any `tf.summary` contained in `Model.call`, metrics added in
    # `Model.compile` will be logged every N batches.
    tb_callback = tf.keras.callbacks.TensorBoard('./logs', update_freq=1)
    model.fit(x_train, y_train, callbacks=[tb_callback])
    ```
  
    Profiling:
  
    ```python
    # Profile a single batch, e.g. the 5th batch.
    tensorboard_callback = tf.keras.callbacks.TensorBoard(
        log_dir='./logs', profile_batch=5)
    model.fit(x_train, y_train, epochs=2, callbacks=[tensorboard_callback])
  
    # Profile a range of batches, e.g. from 10 to 20.
    tensorboard_callback = tf.keras.callbacks.TensorBoard(
        log_dir='./logs', profile_batch=(10,20))
    model.fit(x_train, y_train, epochs=2, callbacks=[tensorboard_callback])
    ```
    """
  
    # pylint: enable=line-too-long
  
    def __init__(self,
                 log_dir='logs',
                 histogram_freq=0,
                 write_graph=True,
                 write_images=False,
                 write_steps_per_second=False,
                 update_freq='epoch',
                 profile_batch=2,
                 embeddings_freq=0,
                 embeddings_metadata=None,
                 **kwargs):
      super(TensorBoard, self).__init__()
      self._supports_tf_logs = True
      self._validate_kwargs(kwargs)
  
      self.log_dir = path_to_string(log_dir)
      self.histogram_freq = histogram_freq
      self.write_graph = write_graph
      self.write_images = write_images
      self.write_steps_per_second = write_steps_per_second
      self.update_freq = 1 if update_freq == 'batch' else update_freq
      self.embeddings_freq = embeddings_freq
      self.embeddings_metadata = embeddings_metadata
      self._init_profile_batch(profile_batch)
      self._epoch = 0
      self._global_train_batch = 0
      self._previous_epoch_iterations = 0
      self._train_accumulated_time = 0
      self._batch_start_time = 0
  
      # Lazily initialized in order to avoid creating event files when
      # not needed.
      self._writers = {}
  
      # Used to restore any existing `SummaryWriter` after training ends.
      self._prev_summary_state = []
  
    def _validate_kwargs(self, kwargs):
      """Handle arguments were supported in V1."""
      if kwargs.get('write_grads', False):
        logging.warning('`write_grads` will be ignored in TensorFlow 2.0 '
                        'for the `TensorBoard` Callback.')
      if kwargs.get('batch_size', False):
        logging.warning('`batch_size` is no longer needed in the '
                        '`TensorBoard` Callback and will be ignored '
                        'in TensorFlow 2.0.')
      if kwargs.get('embeddings_layer_names', False):
        logging.warning('`embeddings_layer_names` is not supported in '
                        'TensorFlow 2.0. Instead, all `Embedding` layers '
                        'will be visualized.')
      if kwargs.get('embeddings_data', False):
        logging.warning('`embeddings_data` is not supported in TensorFlow '
                        '2.0. Instead, all `Embedding` variables will be '
                        'visualized.')
  
      unrecognized_kwargs = set(kwargs.keys()) - {
          'write_grads', 'embeddings_layer_names', 'embeddings_data', 'batch_size'
      }
  
      # Only allow kwargs that were supported in V1.
      if unrecognized_kwargs:
        raise ValueError('Unrecognized arguments in `TensorBoard` '
                         'Callback: ' + str(unrecognized_kwargs))
  
    def set_model(self, model):
      """Sets Keras model and writes graph if specified."""
      self.model = model
      self._log_write_dir = self._get_log_write_dir()
  
      self._train_dir = os.path.join(self._log_write_dir, 'train')
      self._train_step = self.model._train_counter  # pylint: disable=protected-access
  
      self._val_dir = os.path.join(self._log_write_dir, 'validation')
      self._val_step = self.model._test_counter  # pylint: disable=protected-access
  
      self._writers = {}  # Resets writers.
  
      self._should_write_train_graph = False
      if self.write_graph:
        self._write_keras_model_summary()
        self._should_write_train_graph = True
      if self.embeddings_freq:
        self._configure_embeddings()
  
    @property
    def _train_writer(self):
      if 'train' not in self._writers:
        self._writers['train'] = tf.summary.create_file_writer(
            self._train_dir)
      return self._writers['train']
  
    @property
    def _val_writer(self):
      if 'val' not in self._writers:
        self._writers['val'] = tf.summary.create_file_writer(self._val_dir)
      return self._writers['val']
  
    def _get_log_write_dir(self):
      """For multi-worker, only chief should write, others write to '/tmp'."""
      return distributed_file_utils.write_dirpath(self.log_dir,
                                                  self.model.distribute_strategy)
  
    def _delete_tmp_write_dir(self):
      """Deletes tmp write directories for multi-worker."""
      distributed_file_utils.remove_temp_dirpath(self.log_dir,
                                                 self.model.distribute_strategy)
  
    def _write_keras_model_train_graph(self):
      """Writes Keras model train_function graph to TensorBoard."""
      with self._train_writer.as_default():
        with tf.summary.record_if(True):
          train_fn = self.model.train_function
          # If the train_function is a `tf.function`, we can write out a graph
          if hasattr(train_fn, 'function_spec'):
            tf.summary.graph(train_fn._concrete_stateful_fn.graph)  # pylint: disable=protected-access
  
    def _write_keras_model_summary(self):
      """Writes Keras graph network summary to TensorBoard."""
      with self._train_writer.as_default():
        with tf.summary.record_if(True):
          summary_writable = (
              self.model._is_graph_network or  # pylint: disable=protected-access
              self.model.__class__.__name__ == 'Sequential')  # pylint: disable=protected-access
          if summary_writable:
            keras_model_summary('keras', self.model, step=0)
  
    def _configure_embeddings(self):
      """Configure the Projector for embeddings."""
      # TODO(omalleyt): Add integration tests.
      from google.protobuf import text_format
      from keras.layers import embeddings
      from keras.protobuf import projector_config_pb2
  
      config = projector_config_pb2.ProjectorConfig()
      for layer in self.model.layers:
        if isinstance(layer, embeddings.Embedding):
          embedding = config.embeddings.add()
          # Embeddings are always the first layer, so this naming should be
          # consistent in any keras models checkpoints.
          name = 'layer_with_weights-0/embeddings/.ATTRIBUTES/VARIABLE_VALUE'
          embedding.tensor_name = name
  
          if self.embeddings_metadata is not None:
            if isinstance(self.embeddings_metadata, str):
              embedding.metadata_path = self.embeddings_metadata
            else:
              if layer.name in self.embeddings_metadata.keys():
                embedding.metadata_path = self.embeddings_metadata.pop(layer.name)
  
      if self.embeddings_metadata and not isinstance(self.embeddings_metadata,
                                                     str):
        raise ValueError('Unrecognized `Embedding` layer names passed to '
                         '`keras.callbacks.TensorBoard` `embeddings_metadata` '
                         'argument: ' + str(self.embeddings_metadata.keys()))
  
      config_pbtxt = text_format.MessageToString(config)
      path = os.path.join(self._log_write_dir, 'projector_config.pbtxt')
      with tf.io.gfile.GFile(path, 'w') as f:
        f.write(config_pbtxt)
  
    def _push_writer(self, writer, step):
      """Sets the default writer for custom batch-level summaries."""
      if self.update_freq == 'epoch':
        return
  
      summary_state = summary_ops_v2._summary_state  # pylint: disable=protected-access
      self._prev_summary_state.append({
          'is_recording': summary_state.is_recording,
          'writer': summary_state.writer,
          'step': summary_state.step
      })
  
      if self.update_freq == 'epoch':
        should_record = False
        writer = None
      else:
        should_record = lambda: tf.equal(step % self.update_freq, 0)
  
      summary_state.is_recording = should_record
      summary_state.writer = writer
      # TODO(b/151339474): Fix deadlock when not using .value() here.
      tf.summary.experimental.set_step(step.value())
  
    def _pop_writer(self):
      """Pops the current writer."""
      if self.update_freq == 'epoch':
        return
  
      prev_state = self._prev_summary_state.pop()
  
      summary_state = summary_ops_v2._summary_state  # pylint: disable=protected-access
      summary_state.is_recording = prev_state['is_recording']
      summary_state.writer = prev_state['writer']
      tf.summary.experimental.set_step(prev_state['step'])
  
    def _close_writers(self):
      for writer in self._writers.values():
        writer.close()
  
    def _init_profile_batch(self, profile_batch):
      """Validate profile_batch value and set the range of batches to profile.
  
      Args:
        profile_batch: The range of batches to profile. Should be a non-negative
          integer or a comma separated string of pair of positive integers. A pair
          of positive integers signify a range of batches to profile.
  
      Returns:
        A pair of non-negative integers specifying the start and stop batch to
        profile.
  
      Raises:
        ValueError: If profile_batch is not an integer or a comma seperated pair
                    of positive integers.
  
      """
      profile_batch_error_message = (
          'profile_batch must be a non-negative integer or 2-tuple of positive '
          'integers. A pair of positive integers signifies a range of batches '
          'to profile. Found: {}'.format(profile_batch))
  
      # Support legacy way of specifying "start,stop" or "start" as str.
      if isinstance(profile_batch, six.string_types):
        profile_batch = str(profile_batch).split(',')
        profile_batch = tf.nest.map_structure(int, profile_batch)
  
      if isinstance(profile_batch, int):
        self._start_batch = profile_batch
        self._stop_batch = profile_batch
      elif isinstance(profile_batch, (tuple, list)) and len(profile_batch) == 2:
        self._start_batch, self._stop_batch = profile_batch
      else:
        raise ValueError(profile_batch_error_message)
  
      if self._start_batch < 0 or self._stop_batch < self._start_batch:
        raise ValueError(profile_batch_error_message)
  
      if self._start_batch > 0:
        # Warm up and improve the profiling accuracy.
        tf.profiler.experimental.start('')
        tf.profiler.experimental.stop(save=False)
      # True when a trace is running.
      self._is_tracing = False
  
      # Setting `profile_batch=0` disables profiling.
      self._should_trace = not (self._start_batch == 0 and self._stop_batch == 0)
  
    def on_train_begin(self, logs=None):
      self._global_train_batch = 0
      self._previous_epoch_iterations = 0
      self._train_accumulated_time = 0
      self._push_writer(self._train_writer, self._train_step)
  
    def on_train_end(self, logs=None):
      self._pop_writer()
  
      if self._is_tracing:
        self._stop_trace()
  
      self._close_writers()
      self._delete_tmp_write_dir()
  
    def on_test_begin(self, logs=None):
      self._push_writer(self._val_writer, self._val_step)
  
    def on_test_end(self, logs=None):
      self._pop_writer()
  
    def _implements_train_batch_hooks(self):
      return self._should_trace  # Only call batch hooks when tracing is enabled
  
    def on_train_batch_begin(self, batch, logs=None):
      self._global_train_batch += 1
      if self.write_steps_per_second:
        self._batch_start_time = time.time()
      if not self._should_trace:
        return
  
      if self._global_train_batch == self._start_batch:
        self._start_trace()
  
    def on_train_batch_end(self, batch, logs=None):
      if self._should_write_train_graph:
        self._write_keras_model_train_graph()
        self._should_write_train_graph = False
      if self.write_steps_per_second:
        batch_run_time = time.time() - self._batch_start_time
        self._train_accumulated_time += batch_run_time
        summary_ops_v2.scalar('batch_steps_per_second', 1. / batch_run_time)
      if not self._should_trace:
        return
  
      if self._is_tracing and self._global_train_batch >= self._stop_batch:
        self._stop_trace()
  
    def on_epoch_begin(self, epoch, logs=None):
      # Keeps track of epoch for profiling.
      self._epoch = epoch
      if self.write_steps_per_second:
        self._previous_epoch_iterations = self.model.optimizer.iterations.numpy()
        self._train_accumulated_time = 0
  
    def on_epoch_end(self, epoch, logs=None):
      """Runs metrics and histogram summaries at epoch end."""
      self._log_epoch_metrics(epoch, logs)
  
      if self.histogram_freq and epoch % self.histogram_freq == 0:
        self._log_weights(epoch)
  
      if self.embeddings_freq and epoch % self.embeddings_freq == 0:
        self._log_embeddings(epoch)
  
    def _start_trace(self):
      tf.summary.trace_on(graph=True, profiler=False)
      tf.profiler.experimental.start(logdir=self._train_dir)
      self._is_tracing = True
  
    def _stop_trace(self, batch=None):
      """Logs the trace graph to TensorBoard."""
      if batch is None:
        batch = self._stop_batch
      with self._train_writer.as_default():
        with tf.summary.record_if(True):
          # TODO(b/126388999): Remove step info in the summary name.
          tf.summary.trace_export(name='batch_%d' % batch, step=batch)
      tf.profiler.experimental.stop()
      self._is_tracing = False
  
    def _collect_learning_rate(self, logs):
      lr_schedule = getattr(self.model.optimizer, 'lr', None)
      if isinstance(lr_schedule, learning_rate_schedule.LearningRateSchedule):
        logs['learning_rate'] = lr_schedule(self.model.optimizer.iterations)
      return logs
  
    def _compute_steps_per_second(self):
      current_iteration = self.model.optimizer.iterations.numpy()
      steps_per_second = ((current_iteration - self._previous_epoch_iterations) /
                          (self._train_accumulated_time))
      return steps_per_second
  
    def _log_epoch_metrics(self, epoch, logs):
      """Writes epoch metrics out as scalar summaries.
  
      Args:
          epoch: Int. The global step to use for TensorBoard.
          logs: Dict. Keys are scalar summary names, values are scalars.
      """
      if not logs:
        return
  
      train_logs = {k: v for k, v in logs.items() if not k.startswith('val_')}
      val_logs = {k: v for k, v in logs.items() if k.startswith('val_')}
      train_logs = self._collect_learning_rate(train_logs)
      if self.write_steps_per_second:
        train_logs['steps_per_second'] = self._compute_steps_per_second()
  
      with tf.summary.record_if(True):
        if train_logs:
          with self._train_writer.as_default():
            for name, value in train_logs.items():
              summary_ops_v2.scalar('epoch_' + name, value, step=epoch)
        if val_logs:
          with self._val_writer.as_default():
            for name, value in val_logs.items():
              name = name[4:]  # Remove 'val_' prefix.
              summary_ops_v2.scalar('epoch_' + name, value, step=epoch)
  
    def _log_weights(self, epoch):
      """Logs the weights of the Model to TensorBoard."""
      with self._train_writer.as_default():
        with tf.summary.record_if(True):
          for layer in self.model.layers:
            for weight in layer.weights:
              weight_name = weight.name.replace(':', '_')
              summary_ops_v2.histogram(weight_name, weight, step=epoch)
              if self.write_images:
                self._log_weight_as_image(weight, weight_name, epoch)
          self._train_writer.flush()
  
    def _log_weight_as_image(self, weight, weight_name, epoch):
      """Logs a weight as a TensorBoard image."""
      w_img = tf.compat.v1.squeeze(weight)
      shape = K.int_shape(w_img)
      if len(shape) == 1:  # Bias case
        w_img = tf.reshape(w_img, [1, shape[0], 1, 1])
      elif len(shape) == 2:  # Dense layer kernel case
        if shape[0] > shape[1]:
          w_img = tf.compat.v1.transpose(w_img)
          shape = K.int_shape(w_img)
        w_img = tf.reshape(w_img, [1, shape[0], shape[1], 1])
      elif len(shape) == 3:  # ConvNet case
        if K.image_data_format() == 'channels_last':
          # Switch to channels_first to display every kernel as a separate
          # image.
          w_img = tf.compat.v1.transpose(w_img, perm=[2, 0, 1])
          shape = K.int_shape(w_img)
        w_img = tf.reshape(w_img, [shape[0], shape[1], shape[2], 1])
  
      shape = K.int_shape(w_img)
      # Not possible to handle 3D convnets etc.
      if len(shape) == 4 and shape[-1] in [1, 3, 4]:
        summary_ops_v2.image(weight_name, w_img, step=epoch)
  
    def _log_embeddings(self, epoch):
      embeddings_ckpt = os.path.join(self._log_write_dir, 'train',
                                     'keras_embedding.ckpt-{}'.format(epoch))
      self.model.save_weights(embeddings_ckpt)
  
  
  @keras_export('keras.callbacks.ReduceLROnPlateau')
  class ReduceLROnPlateau(Callback):
    """Reduce learning rate when a metric has stopped improving.
  
    Models often benefit from reducing the learning rate by a factor
    of 2-10 once learning stagnates. This callback monitors a
    quantity and if no improvement is seen for a 'patience' number
    of epochs, the learning rate is reduced.
  
    Example:
  
    ```python
    reduce_lr = ReduceLROnPlateau(monitor='val_loss', factor=0.2,
                                  patience=5, min_lr=0.001)
    model.fit(X_train, Y_train, callbacks=[reduce_lr])
    ```
  
    Args:
        monitor: quantity to be monitored.
        factor: factor by which the learning rate will be reduced.
          `new_lr = lr * factor`.
        patience: number of epochs with no improvement after which learning rate
          will be reduced.
        verbose: int. 0: quiet, 1: update messages.
        mode: one of `{'auto', 'min', 'max'}`. In `'min'` mode,
          the learning rate will be reduced when the
          quantity monitored has stopped decreasing; in `'max'` mode it will be
          reduced when the quantity monitored has stopped increasing; in `'auto'`
          mode, the direction is automatically inferred from the name of the
          monitored quantity.
        min_delta: threshold for measuring the new optimum, to only focus on
          significant changes.
        cooldown: number of epochs to wait before resuming normal operation after
          lr has been reduced.
        min_lr: lower bound on the learning rate.
    """
  
    def __init__(self,
                 monitor='val_loss',
                 factor=0.1,
                 patience=10,
                 verbose=0,
                 mode='auto',
                 min_delta=1e-4,
                 cooldown=0,
                 min_lr=0,
                 **kwargs):
      super(ReduceLROnPlateau, self).__init__()
  
      self.monitor = monitor
      if factor >= 1.0:
        raise ValueError('ReduceLROnPlateau ' 'does not support a factor >= 1.0.')
      if 'epsilon' in kwargs:
        min_delta = kwargs.pop('epsilon')
        logging.warning('`epsilon` argument is deprecated and '
                        'will be removed, use `min_delta` instead.')
      self.factor = factor
      self.min_lr = min_lr
      self.min_delta = min_delta
      self.patience = patience
      self.verbose = verbose
      self.cooldown = cooldown
      self.cooldown_counter = 0  # Cooldown counter.
      self.wait = 0
      self.best = 0
      self.mode = mode
      self.monitor_op = None
      self._reset()
  
    def _reset(self):
      """Resets wait counter and cooldown counter.
      """
      if self.mode not in ['auto', 'min', 'max']:
        logging.warning('Learning rate reduction mode %s is unknown, '
                        'fallback to auto mode.', self.mode)
        self.mode = 'auto'
      if (self.mode == 'min' or
          (self.mode == 'auto' and 'acc' not in self.monitor)):
        self.monitor_op = lambda a, b: np.less(a, b - self.min_delta)
        self.best = np.Inf
      else:
        self.monitor_op = lambda a, b: np.greater(a, b + self.min_delta)
        self.best = -np.Inf
      self.cooldown_counter = 0
      self.wait = 0
  
    def on_train_begin(self, logs=None):
      self._reset()
  
    def on_epoch_end(self, epoch, logs=None):
      logs = logs or {}
      logs['lr'] = K.get_value(self.model.optimizer.lr)
      current = logs.get(self.monitor)
      if current is None:
        logging.warning('Learning rate reduction is conditioned on metric `%s` '
                        'which is not available. Available metrics are: %s',
                        self.monitor, ','.join(list(logs.keys())))
  
      else:
        if self.in_cooldown():
          self.cooldown_counter -= 1
          self.wait = 0
  
        if self.monitor_op(current, self.best):
          self.best = current
          self.wait = 0
        elif not self.in_cooldown():
          self.wait += 1
          if self.wait >= self.patience:
            old_lr = K.get_value(self.model.optimizer.lr)
            if old_lr > np.float32(self.min_lr):
              new_lr = old_lr * self.factor
              new_lr = max(new_lr, self.min_lr)
              K.set_value(self.model.optimizer.lr, new_lr)
              if self.verbose > 0:
                print('\nEpoch %05d: ReduceLROnPlateau reducing learning '
                      'rate to %s.' % (epoch + 1, new_lr))
              self.cooldown_counter = self.cooldown
              self.wait = 0
  
    def in_cooldown(self):
      return self.cooldown_counter > 0
  
  
  @keras_export('keras.callbacks.CSVLogger')
  class CSVLogger(Callback):
    """Callback that streams epoch results to a CSV file.
  
    Supports all values that can be represented as a string,
    including 1D iterables such as `np.ndarray`.
  
    Example:
  
    ```python
    csv_logger = CSVLogger('training.log')
    model.fit(X_train, Y_train, callbacks=[csv_logger])
    ```
  
    Args:
        filename: Filename of the CSV file, e.g. `'run/log.csv'`.
        separator: String used to separate elements in the CSV file.
        append: Boolean. True: append if file exists (useful for continuing
            training). False: overwrite existing file.
    """
  
    def __init__(self, filename, separator=',', append=False):
      self.sep = separator
      self.filename = path_to_string(filename)
      self.append = append
      self.writer = None
      self.keys = None
      self.append_header = True
      if six.PY2:
        self.file_flags = 'b'
        self._open_args = {}
      else:
        self.file_flags = ''
        self._open_args = {'newline': '\n'}
      super(CSVLogger, self).__init__()
  
    def on_train_begin(self, logs=None):
      if self.append:
        if tf.io.gfile.exists(self.filename):
          with open(self.filename, 'r' + self.file_flags) as f:
            self.append_header = not bool(len(f.readline()))
        mode = 'a'
      else:
        mode = 'w'
      self.csv_file = io.open(self.filename,
                              mode + self.file_flags,
                              **self._open_args)
  
    def on_epoch_end(self, epoch, logs=None):
      logs = logs or {}
  
      def handle_value(k):
        is_zero_dim_ndarray = isinstance(k, np.ndarray) and k.ndim == 0
        if isinstance(k, six.string_types):
          return k
        elif isinstance(k, collections.abc.Iterable) and not is_zero_dim_ndarray:
          return '"[%s]"' % (', '.join(map(str, k)))
        else:
          return k
  
      if self.keys is None:
        self.keys = sorted(logs.keys())
  
      if self.model.stop_training:
        # We set NA so that csv parsers do not fail for this last epoch.
        logs = dict((k, logs[k]) if k in logs else (k, 'NA') for k in self.keys)
  
      if not self.writer:
  
        class CustomDialect(csv.excel):
          delimiter = self.sep
  
        fieldnames = ['epoch'] + self.keys
  
        self.writer = csv.DictWriter(
            self.csv_file,
            fieldnames=fieldnames,
            dialect=CustomDialect)
        if self.append_header:
          self.writer.writeheader()
  
      row_dict = collections.OrderedDict({'epoch': epoch})
      row_dict.update((key, handle_value(logs[key])) for key in self.keys)
      self.writer.writerow(row_dict)
      self.csv_file.flush()
  
    def on_train_end(self, logs=None):
      self.csv_file.close()
      self.writer = None
  
  
  @keras_export('keras.callbacks.LambdaCallback')
  class LambdaCallback(Callback):
    r"""Callback for creating simple, custom callbacks on-the-fly.
  
    This callback is constructed with anonymous functions that will be called
    at the appropriate time (during `Model.{fit | evaluate | predict}`).
    Note that the callbacks expects positional arguments, as:
  
    - `on_epoch_begin` and `on_epoch_end` expect two positional arguments:
      `epoch`, `logs`
    - `on_batch_begin` and `on_batch_end` expect two positional arguments:
      `batch`, `logs`
    - `on_train_begin` and `on_train_end` expect one positional argument:
      `logs`
  
    Args:
        on_epoch_begin: called at the beginning of every epoch.
        on_epoch_end: called at the end of every epoch.
        on_batch_begin: called at the beginning of every batch.
        on_batch_end: called at the end of every batch.
        on_train_begin: called at the beginning of model training.
        on_train_end: called at the end of model training.
  
    Example:
  
    ```python
    # Print the batch number at the beginning of every batch.
    batch_print_callback = LambdaCallback(
        on_batch_begin=lambda batch,logs: print(batch))
  
    # Stream the epoch loss to a file in JSON format. The file content
    # is not well-formed JSON but rather has a JSON object per line.
    import json
    json_log = open('loss_log.json', mode='wt', buffering=1)
    json_logging_callback = LambdaCallback(
        on_epoch_end=lambda epoch, logs: json_log.write(
            json.dumps({'epoch': epoch, 'loss': logs['loss']}) + '\n'),
        on_train_end=lambda logs: json_log.close()
    )
  
    # Terminate some processes after having finished model training.
    processes = ...
    cleanup_callback = LambdaCallback(
        on_train_end=lambda logs: [
            p.terminate() for p in processes if p.is_alive()])
  
    model.fit(...,
              callbacks=[batch_print_callback,
                         json_logging_callback,
                         cleanup_callback])
    ```
    """
  
    def __init__(self,
                 on_epoch_begin=None,
                 on_epoch_end=None,
                 on_batch_begin=None,
                 on_batch_end=None,
                 on_train_begin=None,
                 on_train_end=None,
                 **kwargs):
      super(LambdaCallback, self).__init__()
      self.__dict__.update(kwargs)
      if on_epoch_begin is not None:
        self.on_epoch_begin = on_epoch_begin
      else:
        self.on_epoch_begin = lambda epoch, logs: None
      if on_epoch_end is not None:
        self.on_epoch_end = on_epoch_end
      else:
        self.on_epoch_end = lambda epoch, logs: None
      if on_batch_begin is not None:
        self.on_batch_begin = on_batch_begin
      else:
        self.on_batch_begin = lambda batch, logs: None
      if on_batch_end is not None:
        self.on_batch_end = on_batch_end
      else:
        self.on_batch_end = lambda batch, logs: None
      if on_train_begin is not None:
        self.on_train_begin = on_train_begin
      else:
        self.on_train_begin = lambda logs: None
      if on_train_end is not None:
        self.on_train_end = on_train_end
      else:
        self.on_train_end = lambda logs: None
  