code: #!/usr/bin/env python
  
  """
  Copyright 2017-2018 Fizyr (https://fizyr.com)
  
  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.
  """
  
  import argparse
  import os
  import sys
  import warnings
  
  import keras
  import keras.preprocessing.image
  import tensorflow as tf
  
  # Allow relative imports when being executed as script.
  if __name__ == "__main__" and __package__ is None:
      sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", ".."))
      import keras_retinanet.bin  # noqa: F401
  
      __package__ = "keras_retinanet.bin"
  
  # Change these to absolute imports if you copy this script outside the keras_retinanet package.
  from .. import layers  # noqa: F401
  from .. import losses
  from .. import models
  from ..callbacks import RedirectModel
  from ..callbacks.eval import Evaluate
  from ..models.retinanet import retinanet_bbox
  from ..preprocessing.csv_generator import CSVGenerator
  from ..utils.anchors import make_shapes_callback
  from ..utils.config import read_config_file, parse_anchor_parameters
  from ..utils.gpu import setup_gpu
  from ..utils.image import random_visual_effect_generator
  from ..utils.keras_version import check_keras_version
  from ..utils.model import freeze as freeze_model
  from ..utils.tf_version import check_tf_version
  from ..utils.transform import random_transform_generator
  
  
  def makedirs(path):
      # Intended behavior: try to create the directory,
      # pass if the directory exists already, fails otherwise.
      # Meant for Python 2.7/3.n compatibility.
      try:
          os.makedirs(path)
      except OSError:
          if not os.path.isdir(path):
              raise
  
  
  def model_with_weights(model, weights, skip_mismatch):
      """ Load weights for model.
  
      Args
          model         : The model to load weights for.
          weights       : The weights to load.
          skip_mismatch : If True, skips layers whose shape of weights doesn't match with the model.
      """
      if weights is not None:
          model.load_weights(weights, by_name=True, skip_mismatch=skip_mismatch)
      return model
  
  
  def create_models(
      backbone_retinanet,
      num_classes,
      weights,
      multi_gpu=0,
      freeze_backbone=False,
      lr=1e-5,
      config=None,
  ):
      """ Creates three models (model, training_model, prediction_model).
  
      Args
          backbone_retinanet : A function to call to create a retinanet model with a given backbone.
          num_classes        : The number of classes to train.
          weights            : The weights to load into the model.
          multi_gpu          : The number of GPUs to use for training.
          freeze_backbone    : If True, disables learning for the backbone.
          config             : Config parameters, None indicates the default configuration.
  
      Returns
          model            : The base model. This is also the model that is saved in snapshots.
          training_model   : The training model. If multi_gpu=0, this is identical to model.
          prediction_model : The model wrapped with utility functions to perform object detection (applies regression values and performs NMS).
      """
  
      modifier = freeze_model if freeze_backbone else None
  
      # load anchor parameters, or pass None (so that defaults will be used)
      anchor_params = None
      num_anchors = None
      if config and "anchor_parameters" in config:
          anchor_params = parse_anchor_parameters(config)
          num_anchors = anchor_params.num_anchors()
  
      # Keras recommends initialising a multi-gpu model on the CPU to ease weight sharing, and to prevent OOM errors.
      # optionally wrap in a parallel model
      if multi_gpu > 1:
          from keras.utils import multi_gpu_model
  
          with tf.device("/cpu:0"):
              model = model_with_weights(
                  backbone_retinanet(
                      num_classes, num_anchors=num_anchors, modifier=modifier
                  ),
                  weights=weights,
                  skip_mismatch=True,
              )
          training_model = multi_gpu_model(model, gpus=multi_gpu)
      else:
          model = model_with_weights(
              backbone_retinanet(num_classes, num_anchors=num_anchors, modifier=modifier),
              weights=weights,
              skip_mismatch=True,
          )
          training_model = model
  
      # make prediction model
      prediction_model = retinanet_bbox(model=model, anchor_params=anchor_params)
  
      # compile model
      training_model.compile(
          loss={"regression": losses.smooth_l1(), "classification": losses.focal()},
          optimizer=keras.optimizers.adam(lr=lr, clipnorm=0.001),
          metrics=["accuracy"],
      )
  
      return model, training_model, prediction_model
  
  
  def create_callbacks(
      model, training_model, prediction_model, validation_generator, args
  ):
      """ Creates the callbacks to use during training.
  
      Args
          model: The base model.
          training_model: The model that is used for training.
          prediction_model: The model that should be used for validation.
          validation_generator: The generator for creating validation data.
          args: parseargs args object.
  
      Returns:
          A list of callbacks used for training.
      """
      callbacks = []
  
      tensorboard_callback = None
  
      if args.tensorboard_dir:
          makedirs(args.tensorboard_dir)
          tensorboard_callback = keras.callbacks.TensorBoard(
              log_dir=args.tensorboard_dir,
              histogram_freq=0,
              batch_size=args.batch_size,
              write_graph=True,
              write_grads=False,
              write_images=False,
              embeddings_freq=0,
              embeddings_layer_names=None,
              embeddings_metadata=None,
          )
  
      if args.evaluation and validation_generator:
          evaluation = Evaluate(
              validation_generator,
              tensorboard=tensorboard_callback,
              weighted_average=args.weighted_average,
          )
          evaluation = RedirectModel(evaluation, prediction_model)
          callbacks.append(evaluation)
  
      # save the model
      if args.snapshots:
          # ensure directory created first; otherwise h5py will error after epoch.
          makedirs(args.snapshot_path)
          checkpoint = keras.callbacks.ModelCheckpoint(
              os.path.join(
                  args.snapshot_path,
                  "{backbone}_{dataset_type}_{{epoch:02d}}.h5".format(
                      backbone=args.backbone, dataset_type=args.dataset_type
                  ),
              ),
              verbose=1,
              # save_best_only=True,
              # monitor="mAP",
              # mode='max'
          )
          checkpoint = RedirectModel(checkpoint, model)
          callbacks.append(checkpoint)
  
      callbacks.append(
          keras.callbacks.ReduceLROnPlateau(
              monitor="loss",
              factor=0.1,
              patience=2,
              verbose=1,
              mode="auto",
              min_delta=0.0001,
              cooldown=0,
              min_lr=0,
          )
      )
  
      if args.tensorboard_dir:
          callbacks.append(tensorboard_callback)
  
      return callbacks
  
  
  def create_generators(args, preprocess_image):
      """ Create generators for training and validation.
  
      Args
          args             : parseargs object containing configuration for generators.
          preprocess_image : Function that preprocesses an image for the network.
      """
      common_args = {
          "batch_size": args.batch_size,
          "config": args.config,
          "image_min_side": args.image_min_side,
          "image_max_side": args.image_max_side,
          "no_resize": args.no_resize,
          "preprocess_image": preprocess_image,
      }
  
      # create random transform generator for augmenting training data
      if args.random_transform:
          transform_generator = random_transform_generator(
              min_rotation=-0.1,
              max_rotation=0.1,
              min_translation=(-0.1, -0.1),
              max_translation=(0.1, 0.1),
              min_shear=-0.1,
              max_shear=0.1,
              min_scaling=(0.9, 0.9),
              max_scaling=(1.1, 1.1),
              flip_x_chance=0.5,
              flip_y_chance=0.5,
          )
          visual_effect_generator = random_visual_effect_generator(
              contrast_range=(0.9, 1.1),
              brightness_range=(-0.1, 0.1),
              hue_range=(-0.05, 0.05),
              saturation_range=(0.95, 1.05),
          )
      else:
          transform_generator = random_transform_generator(flip_x_chance=0.5)
          visual_effect_generator = None
  
      if args.dataset_type == "csv":
          train_generator = CSVGenerator(
              args.annotations,
              args.classes,
              transform_generator=transform_generator,
              visual_effect_generator=visual_effect_generator,
              **common_args
          )
  
          if args.val_annotations:
              validation_generator = CSVGenerator(
                  args.val_annotations, args.classes, shuffle_groups=False, **common_args
              )
          else:
              validation_generator = None
      else:
          raise ValueError("Invalid data type received: {}".format(args.dataset_type))
  
      return train_generator, validation_generator
  
  
  def check_args(parsed_args):
      """ Function to check for inherent contradictions within parsed arguments.
      For example, batch_size < num_gpus
      Intended to raise errors prior to backend initialisation.
  
      Args
          parsed_args: parser.parse_args()
  
      Returns
          parsed_args
      """
  
      if parsed_args.multi_gpu > 1 and parsed_args.batch_size < parsed_args.multi_gpu:
          raise ValueError(
              "Batch size ({}) must be equal to or higher than the number of GPUs ({})".format(
                  parsed_args.batch_size, parsed_args.multi_gpu
              )
          )
  
      if parsed_args.multi_gpu > 1 and parsed_args.snapshot:
          raise ValueError(
              "Multi GPU training ({}) and resuming from snapshots ({}) is not supported.".format(
                  parsed_args.multi_gpu, parsed_args.snapshot
              )
          )
  
      if parsed_args.multi_gpu > 1 and not parsed_args.multi_gpu_force:
          raise ValueError(
              "Multi-GPU support is experimental, use at own risk! Run with --multi-gpu-force if you wish to continue."
          )
  
      if "resnet" not in parsed_args.backbone:
          warnings.warn(
              "Using experimental backbone {}. Only resnet50 has been properly tested.".format(
                  parsed_args.backbone
              )
          )
  
      return parsed_args
  
  
  def parse_args(args):
      """ Parse the arguments.
      """
      parser = argparse.ArgumentParser(
          description="Simple training script for training a RetinaNet network."
      )
      subparsers = parser.add_subparsers(
          help="Arguments for specific dataset types.", dest="dataset_type"
      )
      subparsers.required = True
  
      csv_parser = subparsers.add_parser("csv")
      csv_parser.add_argument(
          "annotations", help="Path to CSV file containing annotations for training."
      )
      csv_parser.add_argument(
          "classes", help="Path to a CSV file containing class label mapping."
      )
      csv_parser.add_argument(
          "--val-annotations",
          help="Path to CSV file containing annotations for validation (optional).",
      )
  
      group = parser.add_mutually_exclusive_group()
      group.add_argument("--snapshot", help="Resume training from a snapshot.")
      group.add_argument(
          "--imagenet-weights",
          help="Initialize the model with pretrained imagenet weights. This is the default behaviour.",
          action="store_const",
          const=True,
          default=True,
      )
      group.add_argument(
          "--weights", help="Initialize the model with weights from a file."
      )
      group.add_argument(
          "--no-weights",
          help="Don't initialize the model with any weights.",
          dest="imagenet_weights",
          action="store_const",
          const=False,
      )
      parser.add_argument(
          "--backbone",
          help="Backbone model used by retinanet.",
          default="resnet50",
          type=str,
      )
      parser.add_argument(
          "--batch-size", help="Size of the batches.", default=1, type=int
      )
      parser.add_argument(
          "--gpu", help="Id of the GPU to use (as reported by nvidia-smi).", type=int
      )
      parser.add_argument(
          "--multi-gpu",
          help="Number of GPUs to use for parallel processing.",
          type=int,
          default=0,
      )
      parser.add_argument(
          "--multi-gpu-force",
          help="Extra flag needed to enable (experimental) multi-gpu support.",
          action="store_true",
      )
      parser.add_argument(
          "--initial-epoch",
          help="Epoch from which to begin the train, useful if resuming from snapshot.",
          type=int,
          default=0,
      )
      parser.add_argument(
          "--epochs", help="Number of epochs to train.", type=int, default=50
      )
      parser.add_argument(
          "--steps", help="Number of steps per epoch.", type=int, default=10000
      )
      parser.add_argument("--lr", help="Learning rate.", type=float, default=1e-5)
      parser.add_argument(
          "--snapshot-path",
          help="Path to store snapshots of models during training (defaults to './snapshots')",
          default="./snapshots",
      )
      parser.add_argument(
          "--tensorboard-dir", help="Log directory for Tensorboard output", default=""
      )  # default='./logs') => https://github.com/tensorflow/tensorflow/pull/34870
      parser.add_argument(
          "--no-snapshots",
          help="Disable saving snapshots.",
          dest="snapshots",
          action="store_false",
      )
      parser.add_argument(
          "--no-evaluation",
          help="Disable per epoch evaluation.",
          dest="evaluation",
          action="store_false",
      )
      parser.add_argument(
          "--freeze-backbone",
          help="Freeze training of backbone layers.",
          action="store_true",
      )
      parser.add_argument(
          "--random-transform",
          help="Randomly transform image and annotations.",
          action="store_true",
      )
      parser.add_argument(
          "--image-min-side",
          help="Rescale the image so the smallest side is min_side.",
          type=int,
          default=800,
      )
      parser.add_argument(
          "--image-max-side",
          help="Rescale the image if the largest side is larger than max_side.",
          type=int,
          default=1333,
      )
      parser.add_argument(
          "--no-resize", help="Don" "t rescale the image.", action="store_true"
      )
      parser.add_argument(
          "--config", help="Path to a configuration parameters .ini file."
      )
      parser.add_argument(
          "--weighted-average",
          help="Compute the mAP using the weighted average of precisions among classes.",
          action="store_true",
      )
      parser.add_argument(
          "--compute-val-loss",
          help="Compute validation loss during training",
          dest="compute_val_loss",
          action="store_true",
      )
  
      # Fit generator arguments
      parser.add_argument(
          "--multiprocessing",
          help="Use multiprocessing in fit_generator.",
          action="store_true",
      )
      parser.add_argument(
          "--workers", help="Number of generator workers.", type=int, default=1
      )
      parser.add_argument(
          "--max-queue-size",
          help="Queue length for multiprocessing workers in fit_generator.",
          type=int,
          default=10,
      )
  
      return check_args(parser.parse_args(args))
  
  
  def main(args=None):
      # parse arguments
      if args is None:
          args = sys.argv[1:]
      args = parse_args(args)
  
      # create object that stores backbone information
      backbone = models.backbone(args.backbone)
  
      # make sure keras and tensorflow are the minimum required version
      check_keras_version()
      check_tf_version()
  
      # optionally choose specific GPU
      if args.gpu is not None:
          setup_gpu(args.gpu)
  
      # optionally load config parameters
      if args.config:
          args.config = read_config_file(args.config)
  
      # create the generators
      train_generator, validation_generator = create_generators(
          args, backbone.preprocess_image
      )
  
      # create the model
      if args.snapshot is not None:
          print("Loading model, this may take a second...")
          model = models.load_model(args.snapshot, backbone_name=args.backbone)
          training_model = model
          anchor_params = None
          if args.config and "anchor_parameters" in args.config:
              anchor_params = parse_anchor_parameters(args.config)
          prediction_model = retinanet_bbox(model=model, anchor_params=anchor_params)
      else:
          weights = args.weights
          # default to imagenet if nothing else is specified
          if weights is None and args.imagenet_weights:
              weights = backbone.download_imagenet()
  
          print("Creating model, this may take a second...")
          model, training_model, prediction_model = create_models(
              backbone_retinanet=backbone.retinanet,
              num_classes=train_generator.num_classes(),
              weights=weights,
              multi_gpu=args.multi_gpu,
              freeze_backbone=args.freeze_backbone,
              lr=args.lr,
              config=args.config,
          )
  
      # print model summary
      print(model.summary())
  
      # this lets the generator compute backbone layer shapes using the actual backbone model
      if "vgg" in args.backbone or "densenet" in args.backbone:
          train_generator.compute_shapes = make_shapes_callback(model)
          if validation_generator:
              validation_generator.compute_shapes = train_generator.compute_shapes
  
      # create the callbacks
      callbacks = create_callbacks(
          model, training_model, prediction_model, validation_generator, args,
      )
  
      if not args.compute_val_loss:
          validation_generator = None
  
      # start training
      return training_model.fit_generator(
          generator=train_generator,
          steps_per_epoch=args.steps,
          epochs=args.epochs,
          verbose=1,
          callbacks=callbacks,
          workers=args.workers,
          use_multiprocessing=args.multiprocessing,
          max_queue_size=args.max_queue_size,
          validation_data=validation_generator,
          initial_epoch=args.initial_epoch,
      )
  
  
  if __name__ == "__main__":
      main()
  
apis: tensorflow.device