code: # Copyright 2020 Google Research. 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.
  # ==============================================================================
  """Common utils."""
  import contextlib
  import os
  import re
  from typing import Text, Tuple, Union
  from absl import logging
  import numpy as np
  import tensorflow.compat.v1 as tf
  import tensorflow.compat.v2 as tf2
  from tensorflow.python.tpu import tpu_function  # pylint:disable=g-direct-tensorflow-import
  # pylint: disable=logging-format-interpolation
  
  
  def srelu_fn(x):
    """Smooth relu: a smooth version of relu."""
    with tf.name_scope('srelu'):
      beta = tf.Variable(20.0, name='srelu_beta', dtype=tf.float32)**2
      beta = tf.cast(beta**2, x.dtype)
      safe_log = tf.math.log(tf.where(x > 0., beta * x + 1., tf.ones_like(x)))
      return tf.where((x > 0.), x - (1. / beta) * safe_log, tf.zeros_like(x))
  
  
  def activation_fn(features: tf.Tensor, act_type: Text):
    """Customized non-linear activation type."""
    if act_type in ('silu', 'swish'):
      return tf.nn.swish(features)
    elif act_type == 'swish_native':
      return features * tf.sigmoid(features)
    elif act_type == 'hswish':
      return features * tf.nn.relu6(features + 3) / 6
    elif act_type == 'relu':
      return tf.nn.relu(features)
    elif act_type == 'relu6':
      return tf.nn.relu6(features)
    elif act_type == 'mish':
      return features * tf.math.tanh(tf.math.softplus(features))
    elif act_type == 'srelu':
      return srelu_fn(features)
    else:
      raise ValueError('Unsupported act_type {}'.format(act_type))
  
  
  def cross_replica_mean(t, num_shards_per_group=None):
    """Calculates the average value of input tensor across TPU replicas."""
    num_shards = tpu_function.get_tpu_context().number_of_shards
    if not num_shards_per_group:
      return tf.tpu.cross_replica_sum(t) / tf.cast(num_shards, t.dtype)
  
    group_assignment = None
    if num_shards_per_group > 1:
      if num_shards % num_shards_per_group != 0:
        raise ValueError(
            'num_shards: %d mod shards_per_group: %d, should be 0' %
            (num_shards, num_shards_per_group))
      num_groups = num_shards // num_shards_per_group
      group_assignment = [[
          x for x in range(num_shards) if x // num_shards_per_group == y
      ] for y in range(num_groups)]
    return tf.tpu.cross_replica_sum(t, group_assignment) / tf.cast(
        num_shards_per_group, t.dtype)
  
  
  def get_ema_vars():
    """Get all exponential moving average (ema) variables."""
    ema_vars = tf.trainable_variables() + \
               tf.get_collection(tf.GraphKeys.MOVING_AVERAGE_VARIABLES)
    for v in tf.global_variables():
      # We maintain mva for batch norm moving mean and variance as well.
      if 'moving_mean' in v.name or 'moving_variance' in v.name:
        ema_vars.append(v)
    return list(set(ema_vars))
  
  
  def get_ckpt_var_map(ckpt_path, ckpt_scope, var_scope, skip_mismatch=None):
    """Get a var map for restoring from pretrained checkpoints.
  
    Args:
      ckpt_path: string. A pretrained checkpoint path.
      ckpt_scope: string. Scope name for checkpoint variables.
      var_scope: string. Scope name for model variables.
      skip_mismatch: skip variables if shape mismatch.
  
    Returns:
      var_map: a dictionary from checkpoint name to model variables.
    """
    logging.info('Init model from checkpoint {}'.format(ckpt_path))
    if not ckpt_scope.endswith('/') or not var_scope.endswith('/'):
      raise ValueError('Please specific scope name ending with /')
    if ckpt_scope.startswith('/'):
      ckpt_scope = ckpt_scope[1:]
    if var_scope.startswith('/'):
      var_scope = var_scope[1:]
  
    var_map = {}
    # Get the list of vars to restore.
    model_vars = tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES, scope=var_scope)
    reader = tf.train.load_checkpoint(ckpt_path)
    ckpt_var_name_to_shape = reader.get_variable_to_shape_map()
    ckpt_var_names = set(reader.get_variable_to_shape_map().keys())
  
    for i, v in enumerate(model_vars):
      if not v.op.name.startswith(var_scope):
        logging.info('skip {} -- does not match scope {}'.format(
            v.op.name, var_scope))
      ckpt_var = ckpt_scope + v.op.name[len(var_scope):]
      if (ckpt_var not in ckpt_var_names and
          v.op.name.endswith('/ExponentialMovingAverage')):
        ckpt_var = ckpt_scope + v.op.name[:-len('/ExponentialMovingAverage')]
  
      if ckpt_var not in ckpt_var_names:
        if 'Momentum' in ckpt_var or 'RMSProp' in ckpt_var:
          # Skip optimizer variables.
          continue
        if skip_mismatch:
          logging.info('skip {} ({}) -- not in ckpt'.format(v.op.name, ckpt_var))
          continue
        raise ValueError('{} is not in ckpt {}'.format(v.op, ckpt_path))
  
      if v.shape != ckpt_var_name_to_shape[ckpt_var]:
        if skip_mismatch:
          logging.info('skip {} ({} vs {}) -- shape mismatch'.format(
              v.op.name, v.shape, ckpt_var_name_to_shape[ckpt_var]))
          continue
        raise ValueError('shape mismatch {} ({} vs {})'.format(
            v.op.name, v.shape, ckpt_var_name_to_shape[ckpt_var]))
  
      if i < 5:
        # Log the first few elements for sanity check.
        logging.info('Init {} from ckpt var {}'.format(v.op.name, ckpt_var))
      var_map[ckpt_var] = v
  
    return var_map
  
  
  def get_ckpt_var_map_ema(ckpt_path, ckpt_scope, var_scope, var_exclude_expr):
    """Get a ema var map for restoring from pretrained checkpoints.
  
    Args:
      ckpt_path: string. A pretrained checkpoint path.
      ckpt_scope: string. Scope name for checkpoint variables.
      var_scope: string. Scope name for model variables.
      var_exclude_expr: string. A regex for excluding variables.
        This is useful for finetuning with different classes, where
        var_exclude_expr='.*class-predict.*' can be used.
  
    Returns:
      var_map: a dictionary from checkpoint name to model variables.
    """
    logging.info('Init model from checkpoint {}'.format(ckpt_path))
    if not ckpt_scope.endswith('/') or not var_scope.endswith('/'):
      raise ValueError('Please specific scope name ending with /')
    if ckpt_scope.startswith('/'):
      ckpt_scope = ckpt_scope[1:]
    if var_scope.startswith('/'):
      var_scope = var_scope[1:]
  
    var_map = {}
    # Get the list of vars to restore.
    model_vars = tf.get_collection(tf.GraphKeys.GLOBAL_VARIABLES, scope=var_scope)
    reader = tf.train.load_checkpoint(ckpt_path)
    ckpt_var_names = set(reader.get_variable_to_shape_map().keys())
    exclude_matcher = re.compile(var_exclude_expr) if var_exclude_expr else None
    for v in model_vars:
      if exclude_matcher and exclude_matcher.match(v.op.name):
        logging.info(
            'skip {} -- excluded by {}'.format(v.op.name, var_exclude_expr))
        continue
  
      if not v.op.name.startswith(var_scope):
        logging.info('skip {} -- does not match scope {}'.format(
            v.op.name, var_scope))
  
      if v.op.name.endswith('/ExponentialMovingAverage'):
        logging.info('skip ema var {}'.format(v.op.name))
        continue
  
      ckpt_var = ckpt_scope + v.op.name[len(var_scope):]
      ckpt_var_ema = ckpt_var + '/ExponentialMovingAverage'
      if ckpt_var_ema in ckpt_var_names:
        var_map[ckpt_var_ema] = v
        logging.info('Init {} from ckpt var {}'.format(v.op.name, ckpt_var_ema))
      elif ckpt_var in ckpt_var_names:
        var_map[ckpt_var] = v
        logging.info('Init {} from ckpt var {}'.format(v.op.name, ckpt_var))
      else:
        logging.info('skip {} ({}) -- not in ckpt'.format(v.op.name, ckpt_var))
    return var_map
  
  
  class TpuBatchNormalization(tf.keras.layers.BatchNormalization):
    """Cross replica batch normalization."""
  
    def __init__(self, fused=False, **kwargs):
      if not kwargs.get('name', None):
        kwargs['name'] = 'tpu_batch_normalization'
      if fused in (True, None):
        raise ValueError('TpuBatchNormalization does not support fused=True.')
      super().__init__(fused=fused, **kwargs)
  
    def _moments(self, inputs, reduction_axes, keep_dims):
      """Compute the mean and variance: it overrides the original _moments."""
      shard_mean, shard_variance = super()._moments(
          inputs, reduction_axes, keep_dims=keep_dims)
  
      num_shards = tpu_function.get_tpu_context().number_of_shards or 1
      num_shards_per_group = min(32, num_shards)  # aggregate up to 32 cores.
      logging.info('TpuBatchNormalization with num_shards_per_group {}'.format(
          num_shards_per_group))
      if num_shards_per_group > 1:
        # Compute variance using: Var[X]= E[X^2] - E[X]^2.
        shard_square_of_mean = tf.math.square(shard_mean)
        shard_mean_of_square = shard_variance + shard_square_of_mean
        group_mean = cross_replica_mean(shard_mean, num_shards_per_group)
        group_mean_of_square = cross_replica_mean(
            shard_mean_of_square, num_shards_per_group)
        group_variance = group_mean_of_square - tf.math.square(group_mean)
        return (group_mean, group_variance)
      else:
        return (shard_mean, shard_variance)
  
    def call(self, inputs, training=None):
      outputs = super().call(inputs, training)
      # A temporary hack for tf1 compatibility with keras batch norm.
      for u in self.updates:
        tf.add_to_collection(tf.GraphKeys.UPDATE_OPS, u)
      return outputs
  
  
  class SyncBatchNormalization(tf.keras.layers.BatchNormalization):
    """Cross replica batch normalization."""
  
    def __init__(self, fused=False, **kwargs):
      if not kwargs.get('name', None):
        kwargs['name'] = 'tpu_batch_normalization'
      if fused in (True, None):
        raise ValueError('SyncBatchNormalization does not support fused=True.')
      super().__init__(fused=fused, **kwargs)
  
    def _moments(self, inputs, reduction_axes, keep_dims):
      """Compute the mean and variance: it overrides the original _moments."""
      shard_mean, shard_variance = super()._moments(
          inputs, reduction_axes, keep_dims=keep_dims)
  
      replica_context = tf.distribute.get_replica_context()
      num_shards = replica_context.num_replicas_in_sync or 1
  
      if num_shards > 1:
        # Compute variance using: Var[X]= E[X^2] - E[X]^2.
        shard_square_of_mean = tf.math.square(shard_mean)
        shard_mean_of_square = shard_variance + shard_square_of_mean
        shard_stack = tf.stack([shard_mean, shard_mean_of_square])
        group_mean, group_mean_of_square = tf.unstack(
            replica_context.all_reduce(tf.distribute.ReduceOp.MEAN, shard_stack))
        group_variance = group_mean_of_square - tf.math.square(group_mean)
        return (group_mean, group_variance)
      else:
        return (shard_mean, shard_variance)
  
    def call(self, inputs, training=None):
      outputs = super().call(inputs, training)
      # A temporary hack for tf1 compatibility with keras batch norm.
      for u in self.updates:
        tf.add_to_collection(tf.GraphKeys.UPDATE_OPS, u)
      return outputs
  
  
  class BatchNormalization(tf.keras.layers.BatchNormalization):
    """Fixed default name of BatchNormalization to match TpuBatchNormalization."""
  
    def __init__(self, **kwargs):
      if not kwargs.get('name', None):
        kwargs['name'] = 'tpu_batch_normalization'
      super().__init__(**kwargs)
  
    def call(self, inputs, training=None):
      outputs = super().call(inputs, training)
      # A temporary hack for tf1 compatibility with keras batch norm.
      for u in self.updates:
        tf.add_to_collection(tf.GraphKeys.UPDATE_OPS, u)
      return outputs
  
  
  def batch_norm_class(is_training, strategy=None):
    if is_training and strategy == 'tpu':
      return TpuBatchNormalization
    elif is_training and strategy == 'gpus':
      # TODO(fsx950223): use SyncBatchNorm after TF bug is fixed (incorrect nccl
      # all_reduce). See https://github.com/tensorflow/tensorflow/issues/41980
      return BatchNormalization
    else:
      return BatchNormalization
  
  
  def batch_normalization(inputs, training=False, strategy=None, **kwargs):
    """A wrapper for TpuBatchNormalization."""
    bn_layer = batch_norm_class(training, strategy)(**kwargs)
    return bn_layer(inputs, training=training)
  
  
  def batch_norm_act(inputs,
                     is_training_bn: bool,
                     act_type: Union[Text, None],
                     init_zero: bool = False,
                     data_format: Text = 'channels_last',
                     momentum: float = 0.99,
                     epsilon: float = 1e-3,
                     strategy: Text = None,
                     name: Text = None):
    """Performs a batch normalization followed by a non-linear activation.
  
    Args:
      inputs: `Tensor` of shape `[batch, channels, ...]`.
      is_training_bn: `bool` for whether the model is training.
      act_type: non-linear relu function type. If None, omits the relu operation.
      init_zero: `bool` if True, initializes scale parameter of batch
        normalization with 0 instead of 1 (default).
      data_format: `str` either "channels_first" for `[batch, channels, height,
        width]` or "channels_last for `[batch, height, width, channels]`.
      momentum: `float`, momentume of batch norm.
      epsilon: `float`, small value for numerical stability.
      strategy: string to specify training strategy for TPU/GPU/CPU.
      name: the name of the batch normalization layer
  
    Returns:
      A normalized `Tensor` with the same `data_format`.
    """
    if init_zero:
      gamma_initializer = tf.zeros_initializer()
    else:
      gamma_initializer = tf.ones_initializer()
  
    if data_format == 'channels_first':
      axis = 1
    else:
      axis = 3
  
    inputs = batch_normalization(
        inputs=inputs,
        axis=axis,
        momentum=momentum,
        epsilon=epsilon,
        center=True,
        scale=True,
        training=is_training_bn,
        strategy=strategy,
        gamma_initializer=gamma_initializer,
        name=name)
  
    if act_type:
      inputs = activation_fn(inputs, act_type)
    return inputs
  
  
  def drop_connect(inputs, is_training, survival_prob):
    """Drop the entire conv with given survival probability."""
    # "Deep Networks with Stochastic Depth", https://arxiv.org/pdf/1603.09382.pdf
    if not is_training:
      return inputs
  
    # Compute tensor.
    batch_size = tf.shape(inputs)[0]
    random_tensor = survival_prob
    random_tensor += tf.random.uniform([batch_size, 1, 1, 1], dtype=inputs.dtype)
    binary_tensor = tf.floor(random_tensor)
    # Unlike conventional way that multiply survival_prob at test time, here we
    # divide survival_prob at training time, such that no addition compute is
    # needed at test time.
    output = inputs / survival_prob * binary_tensor
    return output
  
  
  def num_params_flops(readable_format=True):
    """Return number of parameters and flops."""
    nparams = np.sum(
        [np.prod(v.get_shape().as_list()) for v in tf.trainable_variables()])
    options = tf.profiler.ProfileOptionBuilder.float_operation()
    options['output'] = 'none'
    flops = tf.profiler.profile(
        tf.get_default_graph(), options=options).total_float_ops
    # We use flops to denote multiply-adds, which is counted as 2 ops in tfprof.
    flops = flops // 2
    if readable_format:
      nparams = float(nparams) * 1e-6
      flops = float(flops) * 1e-9
    return nparams, flops
  
  
  conv_kernel_initializer = tf.initializers.variance_scaling()
  dense_kernel_initializer = tf.initializers.variance_scaling()
  
  
  class Pair(tuple):
  
    def __new__(cls, name, value):
      return super().__new__(cls, (name, value))
  
    def __init__(self, name, _):  # pylint: disable=super-init-not-called
      self.name = name
  
  
  def scalar(name, tensor):
    """Stores a (name, Tensor) tuple in a custom collection."""
    logging.info('Adding scale summary {}'.format(Pair(name, tensor)))
    tf.add_to_collection('scalar_summaries', Pair(name, tf.reduce_mean(tensor)))
  
  
  def image(name, tensor):
    logging.info('Adding image summary {}'.format(Pair(name, tensor)))
    tf.add_to_collection('image_summaries', Pair(name, tensor))
  
  
  def get_tpu_host_call(global_step, params):
    """Get TPU host call for summaries."""
    scalar_summaries = tf.get_collection('scalar_summaries')
    if params['img_summary_steps']:
      image_summaries = tf.get_collection('image_summaries')
    else:
      image_summaries = []
    if not scalar_summaries and not image_summaries:
      return None  # No summaries to write.
  
    model_dir = params['model_dir']
    iterations_per_loop = params.get('iterations_per_loop', 100)
    img_steps = params['img_summary_steps']
  
    def host_call_fn(global_step, *args):
      """Training host call. Creates summaries for training metrics."""
      gs = global_step[0]
      with tf2.summary.create_file_writer(
          model_dir, max_queue=iterations_per_loop).as_default():
        with tf2.summary.record_if(True):
          for i, _ in enumerate(scalar_summaries):
            name = scalar_summaries[i][0]
            tensor = args[i][0]
            tf2.summary.scalar(name, tensor, step=gs)
  
        if img_steps:
          with tf2.summary.record_if(lambda: tf.math.equal(gs % img_steps, 0)):
            # Log images every 1k steps.
            for i, _ in enumerate(image_summaries):
              name = image_summaries[i][0]
              tensor = args[i + len(scalar_summaries)]
              tf2.summary.image(name, tensor, step=gs)
  
        return tf.summary.all_v2_summary_ops()
  
    reshaped_tensors = [tf.reshape(t, [1]) for _, t in scalar_summaries]
    reshaped_tensors += [t for _, t in image_summaries]
    global_step_t = tf.reshape(global_step, [1])
    return host_call_fn, [global_step_t] + reshaped_tensors
  
  
  def archive_ckpt(ckpt_eval, ckpt_objective, ckpt_path):
    """Archive a checkpoint if the metric is better."""
    ckpt_dir, ckpt_name = os.path.split(ckpt_path)
  
    saved_objective_path = os.path.join(ckpt_dir, 'best_objective.txt')
    saved_objective = float('-inf')
    if tf.io.gfile.exists(saved_objective_path):
      with tf.io.gfile.GFile(saved_objective_path, 'r') as f:
        saved_objective = float(f.read())
    if saved_objective > ckpt_objective:
      logging.info('Ckpt {} is worse than {}'.format(ckpt_objective,
                                                     saved_objective))
      return False
  
    filenames = tf.io.gfile.glob(ckpt_path + '.*')
    if filenames is None:
      logging.info('No files to copy for checkpoint {}'.format(ckpt_path))
      return False
  
    # clear up the backup folder.
    backup_dir = os.path.join(ckpt_dir, 'backup')
    if tf.io.gfile.exists(backup_dir):
      tf.io.gfile.rmtree(backup_dir)
  
    # rename the old checkpoints to backup folder.
    dst_dir = os.path.join(ckpt_dir, 'archive')
    if tf.io.gfile.exists(dst_dir):
      logging.info('mv {} to {}'.format(dst_dir, backup_dir))
      tf.io.gfile.rename(dst_dir, backup_dir)
  
    # Write checkpoints.
    tf.io.gfile.makedirs(dst_dir)
    for f in filenames:
      dest = os.path.join(dst_dir, os.path.basename(f))
      tf.io.gfile.copy(f, dest, overwrite=True)
    ckpt_state = tf.train.generate_checkpoint_state_proto(
        dst_dir,
        model_checkpoint_path=os.path.join(dst_dir, ckpt_name))
    with tf.io.gfile.GFile(os.path.join(dst_dir, 'checkpoint'), 'w') as f:
      f.write(str(ckpt_state))
    with tf.io.gfile.GFile(os.path.join(dst_dir, 'best_eval.txt'), 'w') as f:
      f.write('%s' % ckpt_eval)
  
    # Update the best objective.
    with tf.io.gfile.GFile(saved_objective_path, 'w') as f:
      f.write('%f' % ckpt_objective)
  
    logging.info('Copying checkpoint {} to {}'.format(ckpt_path, dst_dir))
    return True
  
  
  def parse_image_size(image_size: Union[Text, int, Tuple[int, int]]):
    """Parse the image size and return (height, width).
  
    Args:
      image_size: A integer, a tuple (H, W), or a string with HxW format.
  
    Returns:
      A tuple of integer (height, width).
    """
    if isinstance(image_size, int):
      # image_size is integer, with the same width and height.
      return (image_size, image_size)
  
    if isinstance(image_size, str):
      # image_size is a string with format WxH
      width, height = image_size.lower().split('x')
      return (int(height), int(width))
  
    if isinstance(image_size, tuple):
      return image_size
  
    raise ValueError('image_size must be an int, WxH string, or (height, width)'
                     'tuple. Was %r' % image_size)
  
  
  def get_feat_sizes(image_size: Union[Text, int, Tuple[int, int]],
                     max_level: int):
    """Get feat widths and heights for all levels.
  
    Args:
      image_size: A integer, a tuple (H, W), or a string with HxW format.
      max_level: maximum feature level.
  
    Returns:
      feat_sizes: a list of tuples (height, width) for each level.
    """
    image_size = parse_image_size(image_size)
    feat_sizes = [{'height': image_size[0], 'width': image_size[1]}]
    feat_size = image_size
    for _ in range(1, max_level + 1):
      feat_size = ((feat_size[0] - 1) // 2 + 1, (feat_size[1] - 1) // 2 + 1)
      feat_sizes.append({'height': feat_size[0], 'width': feat_size[1]})
    return feat_sizes
  
  
  def verify_feats_size(feats,
                        feat_sizes,
                        min_level,
                        max_level,
                        data_format='channels_last'):
    """Verify the feature map sizes."""
    expected_output_size = feat_sizes[min_level:max_level + 1]
    for cnt, size in enumerate(expected_output_size):
      h_id, w_id = (2, 3) if data_format == 'channels_first' else (1, 2)
      if feats[cnt].shape[h_id] != size['height']:
        raise ValueError(
            'feats[{}] has shape {} but its height should be {}.'
            '(input_height: {}, min_level: {}, max_level: {}.)'.format(
                cnt, feats[cnt].shape, size['height'], feat_sizes[0]['height'],
                min_level, max_level))
      if feats[cnt].shape[w_id] != size['width']:
        raise ValueError(
            'feats[{}] has shape {} but its width should be {}.'
            '(input_width: {}, min_level: {}, max_level: {}.)'.format(
                cnt, feats[cnt].shape, size['width'], feat_sizes[0]['width'],
                min_level, max_level))
  
  
  def get_precision(strategy: str, mixed_precision: bool = False):
    """Get the precision policy for a given strategy."""
    if mixed_precision:
      if strategy == 'tpu':
        return 'mixed_bfloat16'
  
      if tf.config.experimental.list_physical_devices('GPU'):
        return 'mixed_float16'
  
      # TODO(fsx950223): Fix CPU float16 inference
      # https://github.com/google/automl/issues/504
      logging.warning('float16 is not supported for CPU, use float32 instead')
      return 'float32'
  
    return 'float32'
  
  
  @contextlib.contextmanager
  def float16_scope():
    """Scope class for float16."""
  
    def _custom_getter(getter, *args, **kwargs):
      """Returns a custom getter that methods must be called under."""
      cast_to_float16 = False
      requested_dtype = kwargs['dtype']
      if requested_dtype == tf.float16:
        kwargs['dtype'] = tf.float32
        cast_to_float16 = True
      var = getter(*args, **kwargs)
      if cast_to_float16:
        var = tf.cast(var, tf.float16)
      return var
  
    with tf.variable_scope('', custom_getter=_custom_getter) as varscope:
      yield varscope
  
  
  def set_precision_policy(policy_name: Text = None, loss_scale: bool = False):
    """Set precision policy according to the name.
  
    Args:
      policy_name: precision policy name, one of 'float32', 'mixed_float16',
        'mixed_bfloat16', or None.
      loss_scale: whether to use loss scale (only for training).
    """
    if not policy_name:
      return
  
    assert policy_name in ('mixed_float16', 'mixed_bfloat16', 'float32')
    logging.info('use mixed precision policy name %s', policy_name)
    # TODO(tanmingxing): use tf.keras.layers.enable_v2_dtype_behavior() when it
    # available in stable TF release.
    from tensorflow.python.keras.engine import base_layer_utils  # pylint: disable=g-import-not-at-top,g-direct-tensorflow-import
    base_layer_utils.enable_v2_dtype_behavior()
    # mixed_float16 training is not supported for now, so disable loss_scale.
    # float32 and mixed_bfloat16 do not need loss scale for training.
    if loss_scale:
      policy = tf2.keras.mixed_precision.experimental.Policy(policy_name)
    else:
      policy = tf2.keras.mixed_precision.experimental.Policy(
          policy_name, loss_scale=None)
    tf2.keras.mixed_precision.experimental.set_policy(policy)
  
  
  def build_model_with_precision(pp, mm, ii, tt, *args, **kwargs):
    """Build model with its inputs/params for a specified precision context.
  
    This is highly specific to this codebase, and not intended to be general API.
    Advanced users only. DO NOT use it if you don't know what it does.
    NOTE: short argument names are intended to avoid conficts with kwargs.
  
    Args:
      pp: A string, precision policy name, such as "mixed_float16".
      mm: A function, for rmodel builder.
      ii: A tensor, for model inputs.
      tt: A bool, If true, it is for training; otherwise, it is for eval.
      *args: A list of model arguments.
      **kwargs: A dict, extra model parameters.
  
    Returns:
      the output of mm model.
    """
    if pp == 'mixed_bfloat16':
      set_precision_policy(pp)
      inputs = tf.cast(ii, tf.bfloat16)
      with tf.tpu.bfloat16_scope():
        outputs = mm(inputs, *args, **kwargs)
      set_precision_policy('float32')
    elif pp == 'mixed_float16':
      set_precision_policy(pp, loss_scale=tt)
      inputs = tf.cast(ii, tf.float16)
      with float16_scope():
        outputs = mm(inputs, *args, **kwargs)
      set_precision_policy('float32')
    elif not pp or pp == 'float32':
      outputs = mm(ii, *args, **kwargs)
    else:
      raise ValueError('Unknow precision name {}'.format(pp))
  
    # Users are responsible to convert the dtype of all outputs.
    return outputs
  
apis: tensorflow.compat.v1.zeros_like tensorflow.compat.v1.get_collection tensorflow.compat.v1.math.square tensorflow.compat.v2.summary.image tensorflow.compat.v1.config.experimental.list_physical_devices tensorflow.compat.v1.zeros_initializer tensorflow.compat.v1.profiler.ProfileOptionBuilder.float_operation tensorflow.compat.v2.keras.mixed_precision.experimental.Policy tensorflow.compat.v1.summary.all_v2_summary_ops tensorflow.compat.v1.shape tensorflow.compat.v1.io.gfile.rmtree tensorflow.python.keras.engine.base_layer_utils.enable_v2_dtype_behavior tensorflow.compat.v1.ones_initializer tensorflow.compat.v1.Variable tensorflow.compat.v1.io.gfile.exists tensorflow.compat.v1.floor tensorflow.compat.v1.reduce_mean tensorflow.compat.v1.math.softplus tensorflow.compat.v1.tpu.cross_replica_sum tensorflow.compat.v1.io.gfile.makedirs tensorflow.compat.v1.cast tensorflow.compat.v2.summary.record_if tensorflow.compat.v1.stack tensorflow.compat.v1.get_default_graph tensorflow.compat.v1.nn.relu tensorflow.compat.v1.io.gfile.glob tensorflow.compat.v1.reshape tensorflow.compat.v1.add_to_collection tensorflow.compat.v1.random.uniform tensorflow.compat.v2.keras.mixed_precision.experimental.set_policy tensorflow.compat.v2.summary.scalar tensorflow.compat.v1.io.gfile.copy tensorflow.compat.v1.math.equal tensorflow.compat.v1.sigmoid tensorflow.compat.v2.summary.create_file_writer tensorflow.compat.v1.nn.relu6 tensorflow.compat.v1.trainable_variables tensorflow.compat.v1.tpu.bfloat16_scope tensorflow.compat.v1.ones_like tensorflow.compat.v1.initializers.variance_scaling tensorflow.python.tpu.tpu_function.get_tpu_context tensorflow.compat.v1.train.load_checkpoint tensorflow.compat.v1.global_variables tensorflow.compat.v1.variable_scope tensorflow.compat.v1.distribute.get_replica_context tensorflow.compat.v1.io.gfile.rename tensorflow.compat.v1.io.gfile.GFile tensorflow.compat.v1.nn.swish tensorflow.compat.v1.name_scope