Beispiel #1
0
    def fit(self,
            train_data,
            tuning_data=None,
            time_limit='auto',
            presets=None,
            hyperparameters=None,
            **kwargs):
        """Automatic fit process for image prediction.

        Parameters
        ----------
        train_data : pd.DataFrame or str
            Training data, can be a dataframe like image dataset.
            For dataframe like datasets, `image` and `label` columns are required.
            `image`: raw image paths. `label`: categorical integer id, starting from 0.
            For more details of how to construct a dataset for image predictor, check out:
            `http://preview.d2l.ai/d8/main/image_classification/getting_started.html`.
            If a string is provided, will search for d8 built-in datasets.
        tuning_data : pd.DataFrame or str, default = None
            Another dataset containing validation data reserved for model selection and hyperparameter-tuning,
            can be a dataframe like image dataset.
            If a string is provided, will search for k8 datasets.
            If `None`, the validation dataset will be randomly split from `train_data` according to `holdout_frac`.
        time_limit : int, default = 'auto' (defaults to 2 hours if no presets detected)
            Time limit in seconds, if `None`, will run until all tuning and training finished.
            If `time_limit` is hit during `fit`, the HPO process will interrupt and return the current best configuration.
        presets : list or str or dict, default = ['medium_quality_faster_train']
            List of preset configurations for various arguments in `fit()`. Can significantly impact predictive accuracy, memory-footprint, and inference latency of trained models,
            and various other properties of the returned `predictor`.
            It is recommended to specify presets and avoid specifying most other `fit()` arguments or model hyperparameters prior to becoming familiar with AutoGluon.
            As an example, to get the most accurate overall predictor (regardless of its efficiency), set `presets='best_quality'`.
            To get good quality with faster inference speed, set `presets='good_quality_faster_inference'`
            Any user-specified arguments in `fit()` will override the values used by presets.
            If specifying a list of presets, later presets will override earlier presets if they alter the same argument.
            For precise definitions of the provided presets, see file: `autogluon/vision/configs/presets_configs.py`.
            Users can specify custom presets by passing in a dictionary of argument values as an element to the list.
            Available Presets: ['best_quality', 'high_quality_fast_inference', 'good_quality_faster_inference', 'medium_quality_faster_train']
            It is recommended to only use one `quality` based preset in a given call to `fit()` as they alter many of the same arguments and are not compatible with each-other.

            Note that depending on your specific hardware limitation(# gpu, size of gpu memory...) your mileage may vary a lot, you may choose lower quality presets if necessary, and
            try to reduce `batch_size` if OOM("RuntimeError: CUDA error: out of memory") happens frequently during the `fit`.

            In-depth Preset Info:
                # Best predictive accuracy with little consideration to inference time or model size. Achieve even better results by specifying a large time_limit value.
                # Recommended for applications that benefit from the best possible model accuracy.
                best_quality={
                    'hyperparameters': {
                        'model': Categorical('resnet50_v1b', 'resnet101_v1d', 'resnest200'),
                        'lr': Real(1e-5, 1e-2, log=True),
                        'batch_size': Categorical(8, 16, 32, 64, 128),
                        'epochs': 200,
                        'early_stop_patience': 50
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 1024,
                        'searcher': 'random',
                    },
                    'time_limit': 12*3600,
                },

                # Good predictive accuracy with fast inference.
                # Recommended for applications that require reasonable inference speed and/or model size.
                good_quality_fast_inference={
                    'hyperparameters': {
                        'model': Categorical('resnet50_v1b', 'resnet34_v1b'),
                        'lr': Real(1e-4, 1e-2, log=True),
                        'batch_size': Categorical(8, 16, 32, 64, 128),
                        'epochs': 150,
                        'early_stop_patience': 20
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 512,
                        'searcher': 'random',
                    },
                    'time_limit': 8*3600,
                },

                # Medium predictive accuracy with very fast inference and very fast training time.
                # This is the default preset in AutoGluon, but should generally only be used for quick prototyping.
                medium_quality_faster_train={
                    'hyperparameters': {
                        'model': 'resnet50_v1b',
                        'lr': 0.01,
                        'batch_size': 64,
                        'epochs': 50,
                        'early_stop_patience': 5
                        },
                    'time_limit': 1*3600,
                },

                # Medium predictive accuracy with very fast inference.
                # Comparing with `medium_quality_faster_train` it uses faster model but explores more hyperparameters.
                medium_quality_faster_inference={
                    'hyperparameters': {
                        'model': Categorical('resnet18_v1b', 'mobilenetv3_small'),
                        'lr': Categorical(0.01, 0.005, 0.001),
                        'batch_size': Categorical(64, 128),
                        'epochs': Categorical(50, 100),
                        'early_stop_patience': 10
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 32,
                        'searcher': 'random',
                    },
                    'time_limit': 2*3600,
                },
        hyperparameters : dict, default = None
            Extra hyperparameters for specific models.
            Accepted args includes(not limited to):
            epochs : int, default value based on network
                The `epochs` for model training.
            net : mx.gluon.Block
                The custom network. If defined, the model name in config will be ignored so your
                custom network will be used for training rather than pulling it from model zoo.
            optimizer : mx.Optimizer
                The custom optimizer object. If defined, the optimizer will be ignored in config but this
                object will be used in training instead.
            batch_size : int
                Mini batch size
            lr : float
                Trainer learning rate for optimization process.
            early_stop_patience : int, default=10
                Number of epochs with no improvement after which train is early stopped. Use `None` to disable.
            early_stop_min_delta : float, default=1e-4
                The small delta value to ignore when evaluating the metric. A large delta helps stablize the early
                stopping strategy against tiny fluctuation, e.g. 0.5->0.49->0.48->0.499->0.500001 is still considered as
                a good timing for early stopping.
            early_stop_baseline : float, default=None
                The minimum(baseline) value to trigger early stopping. For example, with `early_stop_baseline=0.5`,
                early stopping won't be triggered if the metric is less than 0.5 even if plateau is detected.
                Use `None` to disable.
            early_stop_max_value : float, default=None
                The max value for metric, early stop training instantly once the max value is achieved. Use `None` to disable.
            You can get the list of accepted hyperparameters in `config.yaml` saved by this predictor.
        **kwargs :
            holdout_frac : float, default = 0.1
                The random split ratio for `tuning_data` if `tuning_data==None`.
            random_state : int, default = None
                The random_state(seed) for shuffling data, only used if `tuning_data==None`.
                Note that the `random_state` only affect the splitting process, not model training.
                If not specified(None), will leave the original random sampling intact.
            nthreads_per_trial : int, default = (# cpu cores)
                Number of CPU threads for each trial, if `None`, will detect the # cores on current instance.
            ngpus_per_trial : int, default = (# gpus)
                Number of GPUs to use for each trial, if `None`, will detect the # gpus on current instance.
            hyperparameter_tune_kwargs: dict, default = None
                num_trials : int, default = 1
                    The limit of HPO trials that can be performed within `time_limit`. The HPO process will be terminated
                    when `num_trials` trials have finished or wall clock `time_limit` is reached, whichever comes first.
                search_strategy : str, default = 'random'
                    Searcher strategy for HPO, 'random' by default.
                    Options include: ‘random’ (random search), ‘bayesopt’ (Gaussian process Bayesian optimization),
                    ‘grid’ (grid search).
                max_reward : float, default = None
                    The reward threashold for stopping criteria. If `max_reward` is reached during HPO, the scheduler
                    will terminate earlier to reduce time cost.
                scheduler_options : dict, default = None
                    Extra options for HPO scheduler, please refer to :class:`autogluon.core.Searcher` for details.
        """
        if self._problem_type is None:
            # options: multiclass, binary, regression
            self._problem_type = MULTICLASS
        assert self._problem_type in (
            MULTICLASS, BINARY,
            REGRESSION), f"Invalid problem_type: {self._problem_type}"
        if self._eval_metric is None:
            if self._problem_type == REGRESSION:
                # options: rmse
                self._eval_metric = 'rmse'
                logger.log(
                    20,
                    'ImagePredictor sets rmse as default eval_metric for regression problems.'
                )
            else:
                # options: accuracy
                self._eval_metric = 'accuracy'
                logger.log(
                    20,
                    'ImagePredictor sets accuracy as default eval_metric for classification problems.'
                )
        # init/validate kwargs
        kwargs = self._validate_kwargs(kwargs)
        # unpack
        num_trials = kwargs['hyperparameter_tune_kwargs']['num_trials']
        nthreads_per_trial = kwargs['nthreads_per_trial']
        ngpus_per_trial = kwargs['ngpus_per_trial']
        holdout_frac = kwargs['holdout_frac']
        random_state = kwargs['random_state']
        scheduler = kwargs['hyperparameter_tune_kwargs']['scheduler']
        searcher = kwargs['hyperparameter_tune_kwargs']['searcher']
        max_reward = kwargs['hyperparameter_tune_kwargs']['max_reward']
        scheduler_options = kwargs['hyperparameter_tune_kwargs'][
            'scheduler_options']
        # deep copy to avoid inplace overwrite
        train_data = copy.deepcopy(train_data)
        tuning_data = copy.deepcopy(tuning_data)

        log_level = verbosity2loglevel(self._verbosity)
        set_logger_verbosity(self._verbosity, logger=logger)
        if presets:
            if not isinstance(presets, list):
                presets = [presets]
            logger.log(20, f'Presets specified: {presets}')

        if time_limit == 'auto':
            # no presets, no user specified time_limit
            time_limit = 7200
            logger.log(20,
                       f'`time_limit=auto` set to `time_limit={time_limit}`.')

        use_rec = False
        if isinstance(train_data, str) and train_data == 'imagenet':
            # FIXME: imagenet does not work, crashes in validating data due to empty DataFrames.
            logger.warning(
                'ImageNet is a huge dataset which cannot be downloaded directly, '
                + 'please follow the data preparation tutorial in GluonCV.' +
                'The following record files(symlinks) will be used: \n' +
                'rec_train : ~/.mxnet/datasets/imagenet/rec/train.rec\n' +
                'rec_train_idx : ~/.mxnet/datasets/imagenet/rec/train.idx\n' +
                'rec_val : ~/.mxnet/datasets/imagenet/rec/val.rec\n' +
                'rec_val_idx : ~/.mxnet/datasets/imagenet/rec/val.idx\n')
            train_data = pd.DataFrame({'image': [], self._label_inner: []})
            tuning_data = pd.DataFrame({'image': [], self._label_inner: []})
            use_rec = True
        if isinstance(train_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if train_data.lower() in names:
                train_data = D8D.get(train_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(
                    f'`train_data` {train_data} is not among valid list {valid_names}'
                )
            if tuning_data is None:
                train_data, tuning_data = train_data.split(1 - holdout_frac)
        if isinstance(tuning_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if tuning_data.lower() in names:
                tuning_data = D8D.get(tuning_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(
                    f'`tuning_data` {tuning_data} is not among valid list {valid_names}'
                )

        # data sanity check
        train_data = self._validate_data(train_data)
        train_labels = _get_valid_labels(train_data)
        self._label_cleaner = LabelCleaner.construct(
            problem_type=self._problem_type,
            y=train_labels,
            y_uncleaned=train_labels)
        train_labels_cleaned = self._label_cleaner.transform(train_labels)
        # converting to internal label set
        _set_valid_labels(train_data, train_labels_cleaned)
        tuning_data_validated = False
        if tuning_data is None:
            train_data, tuning_data, _, _ = generate_train_test_split(
                X=train_data,
                y=train_data[self._label_inner],
                problem_type=self._problem_type,
                test_size=holdout_frac)
            logger.info(
                'Randomly split train_data into train[%d]/validation[%d] splits.',
                len(train_data), len(tuning_data))
            train_data = train_data.reset_index(drop=True)
            tuning_data = tuning_data.reset_index(drop=True)
            tuning_data_validated = True

        train_data = self._validate_data(train_data)
        if isinstance(train_data, self.Dataset):
            train_data = self.Dataset(train_data, classes=train_data.classes)
        if tuning_data is not None and not tuning_data_validated:
            tuning_data = self._validate_data(tuning_data)
            # converting to internal label set
            _set_valid_labels(
                tuning_data,
                self._label_cleaner.transform(_get_valid_labels(tuning_data)))
            if isinstance(tuning_data, self.Dataset):
                tuning_data = self.Dataset(tuning_data,
                                           classes=tuning_data.classes)

        if self._classifier is not None:
            logging.getLogger("ImageClassificationEstimator").propagate = True
            self._classifier._logger.setLevel(log_level)
            self._fit_summary = self._classifier.fit(train_data,
                                                     tuning_data,
                                                     1 - holdout_frac,
                                                     random_state,
                                                     resume=False)
            if hasattr(self._classifier, 'fit_history'):
                self._fit_summary[
                    'fit_history'] = self._classifier.fit_history()
            return self

        # new HPO task
        if time_limit is not None and num_trials is None:
            num_trials = 99999
        if time_limit is None and num_trials is None:
            raise ValueError(
                '`time_limit` and `num_trials` can not be `None` at the same time, '
                'otherwise the training will not be terminated gracefully.')
        config = {
            'log_dir': self._log_dir,
            'num_trials': 99999 if num_trials is None else max(1, num_trials),
            'time_limits':
            2147483647 if time_limit is None else max(1, time_limit),
            'searcher': searcher,
            # needed for gluon-cv TODO: remove after gluon-cv is updated https://github.com/dmlc/gluon-cv/issues/1633
            'search_strategy': searcher,
            'scheduler': scheduler,
        }
        if max_reward is not None:
            config['max_reward'] = max_reward
        if nthreads_per_trial is not None:
            config['nthreads_per_trial'] = nthreads_per_trial
        elif is_fork_enabled():
            # This is needed to address multiprocessing.context.TimeoutError in fork mode
            config['nthreads_per_trial'] = 0
        if ngpus_per_trial is not None:
            config['ngpus_per_trial'] = ngpus_per_trial
        if isinstance(hyperparameters, dict):
            if 'batch_size' in hyperparameters:
                bs = hyperparameters['batch_size']
                _check_gpu_memory_presets(bs, ngpus_per_trial, 4,
                                          256)  # 256MB per sample
            net = hyperparameters.pop('net', None)
            if net is not None:
                config['custom_net'] = net
            optimizer = hyperparameters.pop('optimizer', None)
            if optimizer is not None:
                config['custom_optimizer'] = optimizer
            # check if hyperparameters overwriting existing config
            for k, v in hyperparameters.items():
                if k in config:
                    raise ValueError(
                        f'Overwriting {k} = {config[k]} to {v} by hyperparameters is ambiguous.'
                    )
            config.update(hyperparameters)
        if scheduler_options is not None:
            config.update(scheduler_options)
        if use_rec == True:
            config['use_rec'] = True
        if 'early_stop_patience' not in config:
            config['early_stop_patience'] = 10
        if config['early_stop_patience'] == None:
            config['early_stop_patience'] = -1
        # TODO(zhreshold): expose the transform function(or sign function) for converting custom metrics
        if 'early_stop_baseline' not in config or config[
                'early_stop_baseline'] == None:
            config['early_stop_baseline'] = -np.Inf
        if 'early_stop_max_value' not in config or config[
                'early_stop_max_value'] == None:
            config['early_stop_max_value'] = np.Inf
        # batch size cannot be larger than dataset size
        if ngpus_per_trial is not None and ngpus_per_trial > 1:
            min_value = ngpus_per_trial
        else:
            min_value = 1
        bs = sanitize_batch_size(config.get('batch_size', 16),
                                 min_value=min_value,
                                 max_value=len(train_data))
        config['batch_size'] = bs
        # verbosity
        if log_level > logging.INFO:
            logging.getLogger(
                'gluoncv.auto.tasks.image_classification').propagate = False
            logging.getLogger("ImageClassificationEstimator").propagate = False
            logging.getLogger("ImageClassificationEstimator").setLevel(
                log_level)
        task = _ImageClassification(config=config,
                                    problem_type=self._problem_type)
        # GluonCV can't handle these separately - patching created config
        task.search_strategy = scheduler
        task.scheduler_options['searcher'] = searcher
        task._logger.setLevel(log_level)
        task._logger.propagate = True
        self._train_classes = train_data.classes
        with warnings.catch_warnings(record=True) as w:
            warnings.simplefilter("always")
            with MXNetErrorCatcher() as err:
                self._classifier = task.fit(train_data, tuning_data,
                                            1 - holdout_frac, random_state)
            if err.exc_value is not None:
                raise RuntimeError(err.exc_value + err.hint)
        self._classifier._logger.setLevel(log_level)
        self._classifier._logger.propagate = True
        self._fit_summary = task.fit_summary()
        if hasattr(task, 'fit_history'):
            self._fit_summary['fit_history'] = task.fit_history()
        return self
    def fit(self,
            train_data,
            val_data=None,
            holdout_frac=0.1,
            random_state=None,
            time_limit=12*60*60,
            epochs=None,
            num_trials=1,
            hyperparameters=None,
            search_strategy='random',
            scheduler_options=None,
            nthreads_per_trial=None,
            ngpus_per_trial=None,
            dist_ip_addrs=None,
            verbosity=3):
        """Automatic fit process for image prediction.

        Parameters
        ----------
        train_data : pd.DataFrame or str
            Training data, can be a dataframe like image dataset.
            If a string is provided, will search for k8 datasets.
        val_data : pd.DataFrame or str, default = None
            Training data, can be a dataframe like image dataset.
            If a string is provided, will search for k8 datasets.
            If `None`, the validation dataset will be randomly split from `train_data`.
        holdout_frac : float, default = 0.1
            The random split ratio for `val_data` if `val_data==None`.
        random_state : numpy.random.state, default = None
            The random_state for shuffling, only used if `val_data==None`.
            Note that the `random_state` only affect the splitting process, not model training.
        time_limit : int, default = 43200
            Time limit in seconds, default is 12 hours. If `time_limit` is hit during `fit`, the
            HPO process will interrupt and return the current best configuration.
        epochs : int, default value based on network
            The `epochs` for model training, if `None` is provided, then default `epochs` for model
            will be used.
        num_trials : int, default = 1
            The number of HPO trials. If `None`, will run infinite trials until `time_limit` is met.
        hyperparameters : dict, default = None
            Extra hyperparameters for specific models.
            Accepted args includes(not limited to):
            net : mx.gluon.Block
                The custom network. If defined, the model name in config will be ignored so your
                custom network will be used for training rather than pulling it from model zoo.
            optimizer : mx.Optimizer
                The custom optimizer object. If defined, the optimizer will be ignored in config but this
                object will be used in training instead.
            batch_size : int
                Mini batch size
            learning_rate : float
                Trainer learning rate for optimization process.
            You can get the list of accepted hyperparameters in `config.yaml` saved by this predictor.
        search_strategy : str, default = 'random'
            Searcher strategy for HPO, 'random' by default.
            Options include: ‘random’ (random search), ‘bayesopt’ (Gaussian process Bayesian optimization),
            ‘skopt’ (SKopt Bayesian optimization), ‘grid’ (grid search).
        scheduler_options : dict, default = None
            Extra options for HPO scheduler, please refer to `autogluon.core.Searcher` for details.
        nthreads_per_trial : int, default = (# cpu cores)
            Number of CPU threads for each trial, if `None`, will detect the # cores on current instance.
        ngpus_per_trial : int, default = (# gpus)
            Number of GPUs to use for each trial, if `None`, will detect the # gpus on current instance.
        dist_ip_addrs : list, default = None
            If not `None`, will spawn tasks on distributed nodes.
        verbosity : int, default = 3
            Controls how detailed of a summary to ouput.
            Set <= 0 for no output printing, 1 to print just high-level summary,
            2 to print summary and create plots, >= 3 to print all information produced during fit().
        """
        log_level = verbosity2loglevel(verbosity)
        use_rec = False
        if isinstance(train_data, str) and train_data == 'imagenet':
            logging.warn('ImageNet is a huge dataset which cannot be downloaded directly, ' +
                         'please follow the data preparation tutorial in GluonCV.' +
                         'The following record files(symlinks) will be used: \n' +
                         'rec_train : ~/.mxnet/datasets/imagenet/rec/train.rec\n' +
                         'rec_train_idx : ~/.mxnet/datasets/imagenet/rec/train.idx\n' +
                         'rec_val : ~/.mxnet/datasets/imagenet/rec/val.rec\n' +
                         'rec_val_idx : ~/.mxnet/datasets/imagenet/rec/val.idx\n')
            train_data = pd.DataFrame({'image': [], 'label': []})
            val_data = pd.DataFrame({'image': [], 'label': []})
            use_rec = True
        if isinstance(train_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if train_data.lower() in names:
                train_data = D8D.get(train_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(f'`train_data` {train_data} is not among valid list {valid_names}')
            if val_data is None:
                train_data, val_data = train_data.split(1 - holdout_frac)
        if isinstance(val_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if val_data.lower() in names:
                val_data = D8D.get(val_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(f'`val_data` {val_data} is not among valid list {valid_names}')
        if self._classifier is not None:
            logging.getLogger("ImageClassificationEstimator").propagate = True
            self._classifier._logger.setLevel(log_level)
            self._fit_summary = self._classifier.fit(train_data, val_data, 1 - holdout_frac, random_state, resume=False)
            return

        # new HPO task
        config={'log_dir': self._log_dir,
                'num_trials': 99999 if num_trials is None else max(1, num_trials),
                'time_limits': time_limit,
                'search_strategy': search_strategy,
                }
        if nthreads_per_trial is not None:
            config.update({'nthreads_per_trial': nthreads_per_trial})
        if ngpus_per_trial is not None:
            config.update({'ngpus_per_trial': ngpus_per_trial})
        if dist_ip_addrs is not None:
            config.update({'dist_ip_addrs': dist_ip_addrs})
        if epochs is not None:
            config.update({'epochs': epochs})
        if isinstance(hyperparameters, dict):
            net = hyperparameters.pop('net', None)
            if net is not None:
                config.update({'custom_net': net})
            optimizer = hyperparameters.pop('optimizer', None)
            if optimizer is not None:
                config.update({'custom_optimizer': optimizer})
            # check if hyperparameters overwriting existing config
            for k, v in hyperparameters.items():
                if k in config:
                    raise ValueError(f'Overwriting {k} = {config[k]} to {v} by hyperparameters is ambiguous.')
            config.update(hyperparameters)
        if scheduler_options is not None:
            config.update(scheduler_options)
        if use_rec == True:
            config['use_rec'] = True
        # verbosity
        if log_level > logging.INFO:
            logging.getLogger('gluoncv.auto.tasks.image_classification').propagate = False
            logging.getLogger("ImageClassificationEstimator").propagate = False
            logging.getLogger("ImageClassificationEstimator").setLevel(log_level)
        task = _ImageClassification(config=config)
        task._logger.setLevel(log_level)
        task._logger.propagate = True
        self._classifier = task.fit(train_data, val_data, 1 - holdout_frac, random_state)
        self._classifier._logger.setLevel(log_level)
        self._classifier._logger.propagate = True
        self._fit_summary = task.fit_summary()
Beispiel #3
0
    def fit(self,
            train_data,
            tuning_data=None,
            time_limit=None,
            presets=None,
            hyperparameters=None,
            **kwargs):
        """Automatic fit process for image prediction.

        Parameters
        ----------
        train_data : pd.DataFrame or str
            Training data, can be a dataframe like image dataset.
            For dataframe like datasets, `image` and `label` columns are required.
            `image`: raw image paths. `label`: categorical integer id, starting from 0.
            For more details of how to construct a dataset for image predictor, check out:
            `http://preview.d2l.ai/d8/main/image_classification/getting_started.html`.
            If a string is provided, will search for k8 built-in datasets.
        tuning_data : pd.DataFrame or str, default = None
            Another dataset containing validation data reserved for model selection and hyperparameter-tuning,
            can be a dataframe like image dataset.
            If a string is provided, will search for k8 datasets.
            If `None`, the validation dataset will be randomly split from `train_data` according to `holdout_frac`.
        time_limit : int, default = None
            Time limit in seconds, if not specified, will run until all tuning and training finished.
            If `time_limit` is hit during `fit`, the
            HPO process will interrupt and return the current best configuration.
        presets : list or str or dict, default = ['medium_quality_faster_train']
            List of preset configurations for various arguments in `fit()`. Can significantly impact predictive accuracy, memory-footprint, and inference latency of trained models, 
            and various other properties of the returned `predictor`.
            It is recommended to specify presets and avoid specifying most other `fit()` arguments or model hyperparameters prior to becoming familiar with AutoGluon.
            As an example, to get the most accurate overall predictor (regardless of its efficiency), set `presets='best_quality'`.
            To get good quality with faster inference speed, set `presets='good_quality_faster_inference'`
            Any user-specified arguments in `fit()` will override the values used by presets.
            If specifying a list of presets, later presets will override earlier presets if they alter the same argument.
            For precise definitions of the provided presets, see file: `autogluon/vision/configs/presets_configs.py`.
            Users can specify custom presets by passing in a dictionary of argument values as an element to the list.
            Available Presets: ['best_quality', 'high_quality_fast_inference', 'good_quality_faster_inference', 'medium_quality_faster_train']
            It is recommended to only use one `quality` based preset in a given call to `fit()` as they alter many of the same arguments and are not compatible with each-other.
            
            Note that depending on your specific hardware limitation(# gpu, size of gpu memory...) your mileage may vary a lot, you may choose lower quality presets if necessary, and 
            try to reduce `batch_size` if OOM("RuntimeError: CUDA error: out of memory") happens frequently during the `fit`.

            In-depth Preset Info:
                best_quality={
                    'hyperparameters': {
                        'model': Categorical('resnet50_v1b', 'resnet101_v1d', 'resnest200'),
                        'lr': Real(1e-5, 1e-2, log=True),
                        'batch_size': Categorical(8, 16, 32, 64, 128),
                        'epochs': 200
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 1024,
                        'search_strategy': 'bayesopt'}}
                    Best predictive accuracy with little consideration to inference time or model size. Achieve even better results by specifying a large time_limit value.
                    Recommended for applications that benefit from the best possible model accuracy.

                good_quality_fast_inference={
                    'hyperparameters': {
                        'model': Categorical('resnet50_v1b', 'resnet34_v1b'),
                        'lr': Real(1e-4, 1e-2, log=True),
                        'batch_size': Categorical(8, 16, 32, 64, 128),
                        'epochs': 150
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 512,
                        'search_strategy': 'bayesopt'}}
                    Good predictive accuracy with fast inference.
                    Recommended for applications that require reasonable inference speed and/or model size.

                medium_quality_faster_train={
                    'hyperparameters': {
                        'model': 'resnet50_v1b',
                        'lr': 0.01,
                        'batch_size': 64,
                        'epochs': 50
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 8,
                        'search_strategy': 'random'}}

                    Medium predictive accuracy with very fast inference and very fast training time. 
                    This is the default preset in AutoGluon, but should generally only be used for quick prototyping.

                medium_quality_faster_inference={
                    'hyperparameters': {
                        'model': Categorical('resnet18_v1b', 'mobilenetv3_small'),
                        'lr': Categorical(0.01, 0.005, 0.001),
                        'batch_size': Categorical(64, 128),
                        'epochs': Categorical(50, 100),
                        },
                    'hyperparameter_tune_kwargs': {
                        'num_trials': 32,
                        'search_strategy': 'bayesopt'}}
                    
                    Medium predictive accuracy with very fast inference.
                    Comparing with `medium_quality_faster_train` it uses faster model but explores more hyperparameters.
        hyperparameters : dict, default = None
            Extra hyperparameters for specific models.
            Accepted args includes(not limited to):
            epochs : int, default value based on network
                The `epochs` for model training.
            net : mx.gluon.Block
                The custom network. If defined, the model name in config will be ignored so your
                custom network will be used for training rather than pulling it from model zoo.
            optimizer : mx.Optimizer
                The custom optimizer object. If defined, the optimizer will be ignored in config but this
                object will be used in training instead.
            batch_size : int
                Mini batch size
            lr : float
                Trainer learning rate for optimization process.
            You can get the list of accepted hyperparameters in `config.yaml` saved by this predictor.
        **kwargs :
            holdout_frac : float, default = 0.1
                The random split ratio for `tuning_data` if `tuning_data==None`.
            random_state : int, default = None
                The random_state(seed) for shuffling data, only used if `tuning_data==None`.
                Note that the `random_state` only affect the splitting process, not model training.
                If not specified(None), will leave the original random sampling intact.
            nthreads_per_trial : int, default = (# cpu cores)
                Number of CPU threads for each trial, if `None`, will detect the # cores on current instance.
            ngpus_per_trial : int, default = (# gpus)
                Number of GPUs to use for each trial, if `None`, will detect the # gpus on current instance.
            hyperparameter_tune_kwargs: dict, default = None
                num_trials : int, default = 1
                    The limit of HPO trials that can be performed within `time_limit`. The HPO process will be terminated 
                    when `num_trials` trials have finished or wall clock `time_limit` is reached, whichever comes first.
                search_strategy : str, default = 'random'
                    Searcher strategy for HPO, 'random' by default.
                    Options include: ‘random’ (random search), ‘bayesopt’ (Gaussian process Bayesian optimization),
                    ‘grid’ (grid search).
                max_reward : float, default = None
                    The reward threashold for stopping criteria. If `max_reward` is reached during HPO, the scheduler
                    will terminate earlier to reduce time cost.
                scheduler_options : dict, default = None
                    Extra options for HPO scheduler, please refer to :class:`autogluon.core.Searcher` for details.
        """
        if self._problem_type is None:
            # options: multiclass
            self._problem_type = 'multiclass'
        if self._eval_metric is None:
            # options: accuracy,
            self._eval_metric = 'accuracy'

        # init/validate kwargs
        kwargs = self._validate_kwargs(kwargs)
        # unpack
        num_trials = kwargs['hyperparameter_tune_kwargs']['num_trials']
        nthreads_per_trial = kwargs['nthreads_per_trial']
        ngpus_per_trial = kwargs['ngpus_per_trial']
        holdout_frac = kwargs['holdout_frac']
        random_state = kwargs['random_state']
        search_strategy = kwargs['hyperparameter_tune_kwargs'][
            'search_strategy']
        max_reward = kwargs['hyperparameter_tune_kwargs']['max_reward']
        scheduler_options = kwargs['hyperparameter_tune_kwargs'][
            'scheduler_options']

        log_level = verbosity2loglevel(self._verbosity)
        set_logger_verbosity(self._verbosity, logger=logger)
        if presets:
            if not isinstance(presets, list):
                presets = [presets]
            logger.log(20, f'Presets specified: {presets}')
        use_rec = False
        if isinstance(train_data, str) and train_data == 'imagenet':
            logging.warn(
                'ImageNet is a huge dataset which cannot be downloaded directly, '
                + 'please follow the data preparation tutorial in GluonCV.' +
                'The following record files(symlinks) will be used: \n' +
                'rec_train : ~/.mxnet/datasets/imagenet/rec/train.rec\n' +
                'rec_train_idx : ~/.mxnet/datasets/imagenet/rec/train.idx\n' +
                'rec_val : ~/.mxnet/datasets/imagenet/rec/val.rec\n' +
                'rec_val_idx : ~/.mxnet/datasets/imagenet/rec/val.idx\n')
            train_data = pd.DataFrame({'image': [], 'label': []})
            tuning_data = pd.DataFrame({'image': [], 'label': []})
            use_rec = True
        if isinstance(train_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if train_data.lower() in names:
                train_data = D8D.get(train_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(
                    f'`train_data` {train_data} is not among valid list {valid_names}'
                )
            if tuning_data is None:
                train_data, tuning_data = train_data.split(1 - holdout_frac)
        if isinstance(tuning_data, str):
            from d8.image_classification import Dataset as D8D
            names = D8D.list()
            if tuning_data.lower() in names:
                tuning_data = D8D.get(tuning_data)
            else:
                valid_names = '\n'.join(names)
                raise ValueError(
                    f'`tuning_data` {tuning_data} is not among valid list {valid_names}'
                )
        if self._classifier is not None:
            logging.getLogger("ImageClassificationEstimator").propagate = True
            self._classifier._logger.setLevel(log_level)
            self._fit_summary = self._classifier.fit(train_data,
                                                     tuning_data,
                                                     1 - holdout_frac,
                                                     random_state,
                                                     resume=False)
            return

        # new HPO task
        if time_limit is not None and num_trials is None:
            num_trials = 99999
        if time_limit is None and num_trials is None:
            raise ValueError(
                '`time_limit` and `num_trials` can not be `None` at the same time, '
                'otherwise the training will not be terminated gracefully.')
        config = {
            'log_dir': self._log_dir,
            'num_trials': 99999 if num_trials is None else max(1, num_trials),
            'time_limits':
            2147483647 if time_limit is None else max(1, time_limit),
            'search_strategy': search_strategy,
        }
        if max_reward is not None:
            config['max_reward'] = max_reward
        if nthreads_per_trial is not None:
            config['nthreads_per_trial'] = nthreads_per_trial
        if ngpus_per_trial is not None:
            config['ngpus_per_trial'] = ngpus_per_trial
        if isinstance(hyperparameters, dict):
            if 'batch_size' in hyperparameters:
                bs = hyperparameters['batch_size']
                if ngpus_per_trial is not None and ngpus_per_trial > 1 and bs > 64:
                    # using gpus, check batch size vs. available gpu memory
                    free_gpu_memory = get_gpu_free_memory()
                    if not free_gpu_memory:
                        warnings.warn(
                            'Unable to detect free GPU memory, we are unable to verify '
                            'whether your data mini-batches will fit on the GPU for the specified batch_size.'
                        )
                    elif len(free_gpu_memory) < ngpus_per_trial:
                        warnings.warn(
                            f'Detected GPU memory for {len(free_gpu_memory)} gpus but {ngpus_per_trial} is requested.'
                        )
                    elif sum(free_gpu_memory[:ngpus_per_trial]) / bs < 128:
                        warnings.warn(
                            f'batch-size: {bs} is potentially larger than what your gpus can support '
                            +
                            f'free memory: {free_gpu_memory[:ngpus_per_trial]} '
                            +
                            'Try reducing "batch_size" if you encounter memory issues'
                        )
            net = hyperparameters.pop('net', None)
            if net is not None:
                config['custom_net'] = net
            optimizer = hyperparameters.pop('optimizer', None)
            if optimizer is not None:
                config['custom_optimizer'] = optimizer
            # check if hyperparameters overwriting existing config
            for k, v in hyperparameters.items():
                if k in config:
                    raise ValueError(
                        f'Overwriting {k} = {config[k]} to {v} by hyperparameters is ambiguous.'
                    )
            config.update(hyperparameters)
        if scheduler_options is not None:
            config.update(scheduler_options)
        if use_rec == True:
            config['use_rec'] = True
        # verbosity
        if log_level > logging.INFO:
            logging.getLogger(
                'gluoncv.auto.tasks.image_classification').propagate = False
            logging.getLogger("ImageClassificationEstimator").propagate = False
            logging.getLogger("ImageClassificationEstimator").setLevel(
                log_level)
        task = _ImageClassification(config=config)
        task._logger.setLevel(log_level)
        task._logger.propagate = True
        with warnings.catch_warnings(record=True) as w:
            warnings.simplefilter("always")
            self._classifier = task.fit(train_data, tuning_data,
                                        1 - holdout_frac, random_state)
        self._classifier._logger.setLevel(log_level)
        self._classifier._logger.propagate = True
        self._fit_summary = task.fit_summary()
        return self