NeMo/nemo/core/classes/modelPT.py

# Copyright (c) 2021, NVIDIA CORPORATION.  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.

import copy
import inspect
import os
import uuid
from abc import abstractmethod
from os import path
from os.path import expanduser
from typing import Callable, Dict, List, Optional, Union

import hydra
import torch
from omegaconf import DictConfig, OmegaConf, open_dict
from pytorch_lightning import LightningModule, Trainer
from pytorch_lightning.utilities import rank_zero_only

from nemo.core import optim
from nemo.core.classes.common import Model
from nemo.core.connectors.save_restore_connector import SaveRestoreConnector
from nemo.core.optim import prepare_lr_scheduler
from nemo.utils import logging, model_utils
from nemo.utils.app_state import AppState
from nemo.utils.get_rank import is_global_rank_zero

__all__ = ['ModelPT']


class ModelPT(LightningModule, Model):
    """
    Interface for Pytorch-lightning based NeMo models
    """

    def __init__(self, cfg: DictConfig, trainer: Trainer = None):
        """
        Base class from which all NeMo models should inherit

        Args:
            cfg (DictConfig):  configuration object.
                The cfg object should have (optionally) the following sub-configs:

                * train_ds - to instantiate training dataset
                * validation_ds - to instantiate validation dataset
                * test_ds - to instantiate testing dataset
                * optim - to instantiate optimizer with learning rate scheduler

            trainer (Optional): Pytorch Lightning Trainer instance
        """
        if trainer is not None and not isinstance(trainer, Trainer):
            raise ValueError(
                f"trainer constructor argument must be either None or pytroch_lightning.Trainer. But got {type(trainer)} instead."
            )
        super().__init__()

        """
        Internal global flags that determine core functionality of ModelPT.

        _MODEL_IS_RESTORED:
            This flag determines the context of the model - whether the model is currently being
            restored or not.
            -   When set, it can be assumed that the model's will disable all automatic methods -
                setup_training_data(), setup_validation/test_data() and their multi equivalents.
            -   If a model is being restored from a archive file (tarfile), it can be assumed that
                under this context, the cwd is *inside* the tarfile itself.

        _MODEL_RESTORE_PATH:
            A string path to a a file from which the model is being restored.
            This file can either be a PyTorch Lightning Checkpoint, or a archive (tarfile) that contains
            artifact objects.
            If it is an archive file, during restoration, the cwd will be temporarily moved to inside the
            archive itself.
        """
        # set global vars in AppState
        app_state = AppState()

        # Convert config to a DictConfig
        cfg = model_utils.convert_model_config_to_dict_config(cfg)

        # Convert config to support Hydra 1.0+ instantiation
        cfg = model_utils.maybe_update_config_version(cfg)

        if 'target' not in cfg:
            # This is for Jarvis service.
            OmegaConf.set_struct(cfg, False)
            cfg.target = "{0}.{1}".format(self.__class__.__module__, self.__class__.__name__)
            OmegaConf.set_struct(cfg, True)

        self._cfg = cfg

        self.save_hyperparameters(self._cfg)
        self._train_dl = None
        self._validation_dl = None
        self._test_dl = None
        self._optimizer = None
        self._scheduler = None
        self.trainer = trainer  # reference required for self.*_rank
        self._trainer = self.trainer  # alias for backward compatibility
        self._save_restore_connector = SaveRestoreConnector()

        self._set_model_guid()

        # Set device_id in AppState
        if torch.cuda.is_available() and torch.cuda.current_device() is not None:
            app_state.device_id = torch.cuda.current_device()

        if self._cfg is not None and not self._is_model_being_restored():
            if 'train_ds' in self._cfg and self._cfg.train_ds is not None:
                self.setup_training_data(self._cfg.train_ds)

            if 'validation_ds' in self._cfg and self._cfg.validation_ds is not None:
                self.setup_multiple_validation_data(val_data_config=None)

            if 'test_ds' in self._cfg and self._cfg.test_ds is not None:
                self.setup_multiple_test_data(test_data_config=None)

        else:
            if 'train_ds' in self._cfg and self._cfg.train_ds is not None:
                logging.warning(
                    f"If you intend to do training or fine-tuning, please call the ModelPT.setup_training_data() method "
                    f"and provide a valid configuration file to setup the train data loader.\n"
                    f"Train config : \n{OmegaConf.to_yaml(self._cfg.train_ds)}"
                )

            if 'validation_ds' in self._cfg and self._cfg.validation_ds is not None:
                logging.warning(
                    f"If you intend to do validation, please call the ModelPT.setup_validation_data() or ModelPT.setup_multiple_validation_data() method "
                    f"and provide a valid configuration file to setup the validation data loader(s). \n"
                    f"Validation config : \n{OmegaConf.to_yaml(self._cfg.validation_ds)}"
                )
            if 'test_ds' in self._cfg and self._cfg.test_ds is not None:
                logging.warning(
                    f"Please call the ModelPT.setup_test_data() or ModelPT.setup_multiple_test_data() method "
                    f"and provide a valid configuration file to setup the test data loader(s).\n"
                    f"Test config : \n{OmegaConf.to_yaml(self._cfg.test_ds)}"
                )

        # ModelPT wrappers over subclass implementations
        self.training_step = model_utils.wrap_training_step(self.training_step)

    def __init_subclass__(cls) -> None:
        cls._save_restore_connector = SaveRestoreConnector()

    def register_artifact(
        self, config_path: str, src: str, verify_src_exists: bool = True,
    ):
        """ Register model artifacts with this function. These artifacts (files) will be included inside .nemo file
            when model.save_to("mymodel.nemo") is called.

            How it works:
            1. It always returns existing absolute path which can be used during Model constructor call
                EXCEPTION: src is None or "" in which case nothing will be done and src will be returned
            2. It will add (config_path, model_utils.ArtifactItem()) pair to self.artifacts

            If "src" is local existing path, then it will be returned in absolute path form.
            elif "src" starts with "nemo_file:unique_artifact_name":
                .nemo will be untarred to a temporary folder location and an actual existing path will be returned
            else an error will be raised.

            WARNING: use .register_artifact calls in your models' constructors.
            The returned path is not guaranteed to exist after you have exited your model's constuctor.

            Args:
                config_path (str): Artifact key. Usually corresponds to the model config.
                src (str): Path to artifact.
                verify_src_exists (bool): If set to False, then the artifact is optional and register_artifact will return None even if
                                          src is not found. Defaults to True.
                save_restore_connector (SaveRestoreConnector): Can be overrided to add custom save and restore logic.

            Returns:
                str: If src is not None or empty it always returns absolute path which is guaranteed to exists during model instnce life
        """

        app_state = AppState()

        if src is None or src == "":
            return src

        if not hasattr(self, 'artifacts'):
            self.artifacts = {}

        if self.artifacts is None:
            self.artifacts = {}

        if config_path in self.artifacts.keys():
            logging.warning(
                f"You tried to register an artifact under config key={config_path} but an artifact for "
                f"it has already been registered."
            )

        return self._save_restore_connector.register_artifact(self, config_path, src, verify_src_exists)

    @rank_zero_only
    def save_to(self, save_path: str):
        """
        Saves model instance (weights and configuration) into .nemo file
         You can use "restore_from" method to fully restore instance from .nemo file.

        .nemo file is an archive (tar.gz) with the following:
            model_config.yaml - model configuration in .yaml format. You can deserialize this into cfg argument for model's constructor
            model_wights.chpt - model checkpoint

        Args:
            save_path: Path to .nemo file where model instance should be saved
        """

        # Add NeMo rank check as well
        if not is_global_rank_zero():
            return
        else:
            save_path = os.path.abspath(os.path.expanduser(save_path))
            self._save_restore_connector.save_to(self, save_path)

    @classmethod
    def restore_from(
        cls,
        restore_path: str,
        override_config_path: Optional[Union[OmegaConf, str]] = None,
        map_location: Optional[torch.device] = None,
        strict: bool = True,
        return_config: bool = False,
        save_restore_connector: SaveRestoreConnector = None,
    ):
        """
        Restores model instance (weights and configuration) from .nemo file.

        Args:
            restore_path: path to .nemo file from which model should be instantiated
            override_config_path: path to a yaml config that will override the internal
                config file or an OmegaConf / DictConfig object representing the model config.
            map_location: Optional torch.device() to map the instantiated model to a device.
                By default (None), it will select a GPU if available, falling back to CPU otherwise.
            strict: Passed to load_state_dict. By default True.
            return_config: If set to true, will return just the underlying config of the restored
                model as an OmegaConf DictConfig object without instantiating the model.
            save_restore_connector (SaveRestoreConnector): Can be overrided to add custom save and restore logic.

            Example:
                ```
                model = nemo.collections.asr.models.EncDecCTCModel.restore_from('asr.nemo')
                assert isinstance(model, nemo.collections.asr.models.EncDecCTCModel)
                ```

        Returns:
            An instance of type cls or its underlying config (if return_config is set).
        """

        if save_restore_connector is None:
            save_restore_connector = SaveRestoreConnector()

        restore_path = os.path.abspath(os.path.expanduser(restore_path))
        if not path.exists(restore_path):
            raise FileNotFoundError(f"Can't find {restore_path}")

        app_state = AppState()
        app_state.model_restore_path = restore_path

        cls.update_save_restore_connector(save_restore_connector)
        instance = cls._save_restore_connector.restore_from(
            cls, restore_path, override_config_path, map_location, strict, return_config
        )
        if isinstance(instance, ModelPT):
            instance._save_restore_connector = save_restore_connector
        return instance

    @classmethod
    def load_from_checkpoint(
        cls,
        checkpoint_path: str,
        *args,
        map_location: Optional[Union[Dict[str, str], str, torch.device, int, Callable]] = None,
        hparams_file: Optional[str] = None,
        strict: bool = True,
        **kwargs,
    ):
        """
        Loads ModelPT from checkpoint, with some maintenance of restoration.
        For documentation, please refer to LightningModule.load_from_checkpoin() documentation.
        """
        checkpoint = None
        try:
            cls._set_model_restore_state(is_being_restored=True)

            checkpoint = super().load_from_checkpoint(
                checkpoint_path=checkpoint_path,
                *args,
                map_location=map_location,
                hparams_file=hparams_file,
                strict=strict,
                **kwargs,
            )

        finally:
            cls._set_model_restore_state(is_being_restored=False)
        return checkpoint

    @abstractmethod
    def setup_training_data(self, train_data_config: Union[DictConfig, Dict]):
        """
        Setups data loader to be used in training

        Args:
            train_data_layer_config: training data layer parameters.
        Returns:

        """
        pass

    @abstractmethod
    def setup_validation_data(self, val_data_config: Union[DictConfig, Dict]):
        """
        Setups data loader to be used in validation
        Args:

            val_data_layer_config: validation data layer parameters.
        Returns:

        """
        pass

    def setup_test_data(self, test_data_config: Union[DictConfig, Dict]):
        """
        (Optionally) Setups data loader to be used in test

        Args:
            test_data_layer_config: test data layer parameters.
        Returns:

        """
        raise NotImplementedError()

    def setup_multiple_validation_data(self, val_data_config: Union[DictConfig, Dict]):
        """
        (Optionally) Setups data loader to be used in validation, with support for multiple data loaders.

        Args:
            val_data_layer_config: validation data layer parameters.
        """
        # Set some placeholder overriden by helper method
        self._val_dl_idx = 0
        self._validation_names = None
        self._validation_dl = None  # type: torch.utils.data.DataLoader

        # preserve config
        self._update_dataset_config(dataset_name='validation', config=val_data_config)

        try:
            self._multi_dataset_mode = True
            model_utils.resolve_validation_dataloaders(model=self)
        finally:
            self._multi_dataset_mode = False

        if self._validation_names is None:
            if self._validation_dl is not None and type(self._validation_dl) in [list, tuple]:
                self._validation_names = ['val_{}_'.format(idx) for idx in range(len(self._validation_dl))]

    def setup_multiple_test_data(self, test_data_config: Union[DictConfig, Dict]):
        """
        (Optionally) Setups data loader to be used in test, with support for multiple data loaders.

        Args:
            test_data_layer_config: test data layer parameters.
        """
        # Set some placeholder overriden by helper method
        self._test_dl_idx = 0
        self._test_names = None
        self._test_dl = None  # type: torch.utils.data.DataLoader

        # preserve config
        self._update_dataset_config(dataset_name='test', config=test_data_config)

        try:
            self._multi_dataset_mode = True
            model_utils.resolve_test_dataloaders(model=self)
        finally:
            self._multi_dataset_mode = False

        if self._test_names is None:
            if self._test_dl is not None and type(self._test_dl) in [list, tuple]:
                self._test_names = ['test_{}_'.format(idx) for idx in range(len(self._test_dl))]

    def setup_optimization(self, optim_config: Optional[Union[DictConfig, Dict]] = None):
        """
        Prepares an optimizer from a string name and its optional config parameters.

        Args:
            optim_config: A dictionary containing the following keys:

                * "lr": mandatory key for learning rate. Will raise ValueError if not provided.
                * "optimizer": string name pointing to one of the available optimizers in the registry. \
                If not provided, defaults to "adam".
                * "opt_args": Optional list of strings, in the format "arg_name=arg_value". \
                The list of "arg_value" will be parsed and a dictionary of optimizer kwargs \
                will be built and supplied to instantiate the optimizer.
        """
        # If config was not explicitly passed to us
        if optim_config is None:
            # See if internal config has `optim` namespace
            if self._cfg is not None and hasattr(self._cfg, 'optim'):
                optim_config = self._cfg.optim

        # If config is still None, or internal config has no Optim, return without instantiation
        if optim_config is None:
            logging.info('No optimizer config provided, therefore no optimizer was created')
            return

        else:
            # Preserve the configuration
            if not isinstance(optim_config, DictConfig):
                optim_config = OmegaConf.create(optim_config)

            # See if internal config has `optim` namespace before preservation
            if self._cfg is not None and hasattr(self._cfg, 'optim'):
                if self._cfg.optim is None:
                    self._cfg.optim = copy.deepcopy(optim_config)
                else:
                    with open_dict(self._cfg.optim):
                        self._cfg.optim = copy.deepcopy(optim_config)

        # Setup optimizer and scheduler
        if optim_config is not None and isinstance(optim_config, DictConfig):
            optim_config = OmegaConf.to_container(optim_config, resolve=True)

        if self._trainer is None:
            logging.warning(f"Trainer wasn't specified in model constructor. Make sure that you really wanted it.")

        if 'sched' in optim_config and self._trainer is not None:
            if not isinstance(self._trainer.accumulate_grad_batches, int):
                raise ValueError("We do not currently support gradient acculumation that is not an integer.")
            if self._trainer.max_steps is None:
                # Store information needed to calculate max_steps
                optim_config['sched']['t_max_epochs'] = self._trainer.max_epochs
                optim_config['sched']['t_accumulate_grad_batches'] = self._trainer.accumulate_grad_batches
                optim_config['sched']['t_limit_train_batches'] = self._trainer.limit_train_batches
                if self._trainer.distributed_backend is None:
                    optim_config['sched']['t_num_workers'] = self._trainer.num_gpus or 1
                elif self._trainer.distributed_backend == "ddp_cpu":
                    optim_config['sched']['t_num_workers'] = self._trainer.num_processes * self._trainer.num_nodes
                elif self._trainer.distributed_backend == "ddp":
                    optim_config['sched']['t_num_workers'] = self._trainer.num_gpus * self._trainer.num_nodes
                else:
                    logging.warning(
                        f"The lightning trainer received accelerator: {self._trainer.distributed_backend}. We "
                        "recommend to use 'ddp' instead."
                    )
                    optim_config['sched']['t_num_workers'] = self._trainer.num_gpus * self._trainer.num_nodes
            else:
                optim_config['sched']['max_steps'] = self._trainer.max_steps

        # Force into DictConfig from nested structure
        optim_config = OmegaConf.create(optim_config)
        # Get back nested dict so we its mutable
        optim_config = OmegaConf.to_container(optim_config, resolve=True)

        # Extract scheduler config if inside optimizer config
        if 'sched' in optim_config:
            scheduler_config = optim_config.pop('sched')
        else:
            scheduler_config = None

        # Check if caller provided optimizer name, default to Adam otherwise
        optimizer_cls = optim_config.get('_target_', None)

        if optimizer_cls is None:
            # Try to get optimizer name for dynamic resolution, defaulting to Adam
            optimizer_name = optim_config.get('name', 'adam')
        else:
            if inspect.isclass(optimizer_cls):
                optimizer_name = optimizer_cls.__name__.lower()
            else:
                # resolve the class name (lowercase) from the class path if not provided
                optimizer_name = optimizer_cls.split(".")[-1].lower()

        # We are guarenteed to have lr since it is required by the argparser
        # But maybe user forgot to pass it to this function
        lr = optim_config.get('lr', None)

        # Check if caller has optimizer kwargs, default to empty dictionary
        if 'args' in optim_config:
            optimizer_args = optim_config.pop('args')
            optimizer_args = optim.parse_optimizer_args(optimizer_name, optimizer_args)
        else:
            optimizer_args = copy.deepcopy(optim_config)

            # Remove extra parameters from optimizer_args nest
            # Assume all other parameters are to be passed into optimizer constructor
            optimizer_args.pop('name', None)
            optimizer_args.pop('cls', None)
            optimizer_args.pop('lr', None)

        # Adaptive schedulers don't need `lr`
        if lr is not None:
            optimizer_args['lr'] = lr

        # Actually instantiate the optimizer
        if optimizer_cls is not None:
            if inspect.isclass(optimizer_cls):
                optimizer = optimizer_cls(self.parameters(), **optimizer_args)
                logging.info("Optimizer config = %s", str(optimizer))

                self._optimizer = optimizer

            else:
                # Attempt class path resolution
                try:
                    optimizer_cls = OmegaConf.create({'_target_': optimizer_cls})
                    if lr is not None:
                        optimizer_config = {'lr': lr}
                    else:
                        optimizer_config = {}
                    optimizer_config.update(optimizer_args)

                    optimizer_instance = hydra.utils.instantiate(
                        optimizer_cls, self.parameters(), **optimizer_config
                    )  # type: DictConfig

                    logging.info("Optimizer config = %s", str(optimizer_instance))

                    self._optimizer = optimizer_instance

                except Exception as e:
                    logging.error(
                        "Could not instantiate class path - {} with kwargs {}".format(
                            optimizer_cls, str(optimizer_config)
                        )
                    )
                    raise e

        else:
            optimizer = optim.get_optimizer(optimizer_name)
            optimizer = optimizer(self.parameters(), **optimizer_args)

            logging.info("Optimizer config = %s", str(optimizer))

            self._optimizer = optimizer

        # Try to instantiate scheduler for optimizer
        self._scheduler = prepare_lr_scheduler(
            optimizer=self._optimizer, scheduler_config=scheduler_config, train_dataloader=self._train_dl
        )

        # Return the optimizer with/without scheduler
        # This return allows multiple optimizers or schedulers to be created
        return self._optimizer, self._scheduler

    def configure_optimizers(self):
        self.setup_optimization()

        if self._scheduler is None:
            return self._optimizer
        else:
            return [self._optimizer], [self._scheduler]

    def train_dataloader(self):
        if self._train_dl is not None:
            return self._train_dl

    def val_dataloader(self):
        if self._validation_dl is not None:
            return self._validation_dl

    def test_dataloader(self):
        if self._test_dl is not None:
            return self._test_dl

    def validation_epoch_end(
        self, outputs: Union[List[Dict[str, torch.Tensor]], List[List[Dict[str, torch.Tensor]]]]
    ) -> Optional[Dict[str, Dict[str, torch.Tensor]]]:
        """
        Default DataLoader for Validation set which automatically supports multiple data loaders
        via `multi_validation_epoch_end`.

        If multi dataset support is not required, override this method entirely in base class.
        In such a case, there is no need to implement `multi_validation_epoch_end` either.

        .. note::
            If more than one data loader exists, and they all provide `val_loss`,
            only the `val_loss` of the first data loader will be used by default.
            This default can be changed by passing the special key `val_dl_idx: int`
            inside the `validation_ds` config.

        Args:
            outputs: Single or nested list of tensor outputs from one or more data loaders.

        Returns:
            A dictionary containing the union of all items from individual data_loaders,
            along with merged logs from all data loaders.
        """
        # Case where we dont provide data loaders
        if outputs is not None and len(outputs) == 0:
            return {}

        # Case where we provide exactly 1 data loader
        if type(outputs[0]) == dict:
            output_dict = self.multi_validation_epoch_end(outputs, dataloader_idx=0)

            if output_dict is not None and 'log' in output_dict:
                self.log_dict(output_dict.pop('log'), on_epoch=True)

            return output_dict

        else:  # Case where we provide more than 1 data loader
            output_dict = {'log': {}}

            # The output is a list of list of dicts, outer list corresponds to dataloader idx
            for dataloader_idx, val_outputs in enumerate(outputs):
                # Get prefix and dispatch call to multi epoch end
                dataloader_prefix = self.get_validation_dataloader_prefix(dataloader_idx)
                dataloader_logs = self.multi_validation_epoch_end(val_outputs, dataloader_idx=dataloader_idx)

                # If result was not provided, generate empty dict
                dataloader_logs = dataloader_logs or {}

                # Perform `val_loss` resolution first (if provided outside logs)
                if 'val_loss' in dataloader_logs:
                    if 'val_loss' not in output_dict and dataloader_idx == self._val_dl_idx:
                        output_dict['val_loss'] = dataloader_logs['val_loss']

                # For every item in the result dictionary
                for k, v in dataloader_logs.items():
                    # If the key is `log`
                    if k == 'log':
                        # Parse every element of the log, and attach the prefix name of the data loader
                        log_dict = {}

                        for k_log, v_log in v.items():
                            # If we are logging the metric, but dont provide it at result level,
                            # store it twice - once in log and once in result level.
                            # Also mark log with prefix name to avoid log level clash with other data loaders
                            if k_log not in output_dict['log'] and dataloader_idx == self._val_dl_idx:
                                new_k_log = k_log

                                # Also insert duplicate key with prefix for ease of comparison / avoid name clash
                                log_dict[dataloader_prefix + k_log] = v_log

                            else:
                                # Simply prepend prefix to key and save
                                new_k_log = dataloader_prefix + k_log

                            # Store log value
                            log_dict[new_k_log] = v_log

                        # Update log storage of individual data loader
                        output_logs = output_dict['log']
                        output_logs.update(log_dict)

                        # Update global log storage
                        output_dict['log'] = output_logs

                    else:
                        # If any values are stored outside 'log', simply prefix name and store
                        new_k = dataloader_prefix + k
                        output_dict[new_k] = v

            if 'log' in output_dict:
                self.log_dict(output_dict.pop('log'), on_epoch=True)

            # return everything else
            return output_dict

    def test_epoch_end(
        self, outputs: Union[List[Dict[str, torch.Tensor]], List[List[Dict[str, torch.Tensor]]]]
    ) -> Optional[Dict[str, Dict[str, torch.Tensor]]]:
        """
        Default DataLoader for Test set which automatically supports multiple data loaders
        via `multi_test_epoch_end`.

        If multi dataset support is not required, override this method entirely in base class.
        In such a case, there is no need to implement `multi_test_epoch_end` either.

        .. note::
            If more than one data loader exists, and they all provide `test_loss`,
            only the `test_loss` of the first data loader will be used by default.
            This default can be changed by passing the special key `test_dl_idx: int`
            inside the `test_ds` config.

        Args:
            outputs: Single or nested list of tensor outputs from one or more data loaders.

        Returns:
            A dictionary containing the union of all items from individual data_loaders,
            along with merged logs from all data loaders.
        """
        # Case where we dont provide data loaders
        if outputs is not None and len(outputs) == 0:
            return {}

        # Case where we provide exactly 1 data loader
        if type(outputs[0]) == dict:
            output_dict = self.multi_test_epoch_end(outputs, dataloader_idx=0)

            if output_dict is not None and 'log' in output_dict:
                self.log_dict(output_dict.pop('log'), on_epoch=True)

            return output_dict

        else:  # Case where we provide more than 1 data loader
            output_dict = {'log': {}}

            # The output is a list of list of dicts, outer list corresponds to dataloader idx
            for dataloader_idx, test_outputs in enumerate(outputs):
                # Get prefix and dispatch call to multi epoch end
                dataloader_prefix = self.get_test_dataloader_prefix(dataloader_idx)
                dataloader_logs = self.multi_test_epoch_end(test_outputs, dataloader_idx=dataloader_idx)

                # If result was not provided, generate empty dict
                dataloader_logs = dataloader_logs or {}

                # Perform `test_loss` resolution first (if provided outside logs)
                if 'test_loss' in dataloader_logs:
                    if 'test_loss' not in output_dict and dataloader_idx == self._test_dl_idx:
                        output_dict['test_loss'] = dataloader_logs['test_loss']

                # For every item in the result dictionary
                for k, v in dataloader_logs.items():
                    # If the key is `log`
                    if k == 'log':
                        # Parse every element of the log, and attach the prefix name of the data loader
                        log_dict = {}
                        for k_log, v_log in v.items():
                            # If we are logging the loss, but dont provide it at result level,
                            # store it twice - once in log and once in result level.
                            # Also mark log with prefix name to avoid log level clash with other data loaders
                            if k_log not in output_dict['log'] and dataloader_idx == self._test_dl_idx:
                                new_k_log = k_log

                                # Also insert duplicate key with prefix for ease of comparison / avoid name clash
                                log_dict[dataloader_prefix + k_log] = v_log

                            else:
                                # Simply prepend prefix to key and save
                                new_k_log = dataloader_prefix + k_log

                            log_dict[new_k_log] = v_log

                        # Update log storage of individual data loader
                        output_logs = output_dict.get('log', {})
                        output_logs.update(log_dict)

                        # Update global log storage
                        output_dict['log'] = output_logs

                    else:
                        # If any values are stored outside 'log', simply prefix name and store
                        new_k = dataloader_prefix + k
                        output_dict[new_k] = v

            if 'log' in output_dict:
                self.log_dict(output_dict.pop('log'), on_epoch=True)

            # return everything else
            return output_dict

    def multi_validation_epoch_end(
        self, outputs: List[Dict[str, torch.Tensor]], dataloader_idx: int = 0
    ) -> Optional[Dict[str, Dict[str, torch.Tensor]]]:
        """
        Adds support for multiple validation datasets. Should be overriden by subclass,
        so as to obtain appropriate logs for each of the dataloaders.

        Args:
            outputs: Same as that provided by LightningModule.validation_epoch_end()
                for a single dataloader.
            dataloader_idx: int representing the index of the dataloader.

        Returns:
            A dictionary of values, optionally containing a sub-dict `log`,
            such that the values in the log will be pre-pended by the dataloader prefix.
        """
        logging.warning(
            "Multi data loader support has been enabled, but "
            "`multi_validation_epoch_end(outputs, dataloader_idx) has not been implemented.\n"
            "If you require multi data loader support for validation sets, please override this method.\n"
            "If you do not require multi data loader support, please instead override "
            "`validation_epoch_end(outputs)."
        )

    def multi_test_epoch_end(
        self, outputs: List[Dict[str, torch.Tensor]], dataloader_idx: int = 0
    ) -> Optional[Dict[str, Dict[str, torch.Tensor]]]:
        """
        Adds support for multiple test datasets. Should be overriden by subclass,
        so as to obtain appropriate logs for each of the dataloaders.

        Args:
            outputs: Same as that provided by LightningModule.validation_epoch_end()
                for a single dataloader.
            dataloader_idx: int representing the index of the dataloader.

        Returns:
            A dictionary of values, optionally containing a sub-dict `log`,
            such that the values in the log will be pre-pended by the dataloader prefix.
        """
        logging.warning(
            "Multi data loader support has been enabled, but "
            "`multi_test_epoch_end(outputs, dataloader_idx) has not been implemented.\n"
            "If you require multi data loader support for validation sets, please override this method.\n"
            "If you do not require multi data loader support, please instead override "
            "`test_epoch_end(outputs)."
        )

    def get_validation_dataloader_prefix(self, dataloader_idx: int = 0) -> str:
        """
        Get the name of one or more data loaders, which will be prepended to all logs.

        Args:
            dataloader_idx: Index of the data loader.

        Returns:
            str name of the data loader at index provided.
        """
        return self._validation_names[dataloader_idx]

    def get_test_dataloader_prefix(self, dataloader_idx: int = 0) -> str:
        """
        Get the name of one or more data loaders, which will be prepended to all logs.

        Args:
            dataloader_idx: Index of the data loader.

        Returns:
            str name of the data loader at index provided.
        """
        return self._test_names[dataloader_idx]

    @rank_zero_only
    def maybe_init_from_pretrained_checkpoint(self, cfg: OmegaConf, map_location: str = 'cpu'):
        """
        Initializes a given model with the parameters obtained via specific config arguments.
        The state dict of the provided model will be updated with `strict=False` setting so as to prevent
        requirement of exact model parameters matching.

        Initializations:
            init_from_nemo_model: Str path to a .nemo model, which will be instantiated in order
                to extract the state dict.

            init_from_pretrained_model: Str name of a pretrained model checkpoint (obtained via cloud).
                The model will be downloaded (or a cached copy will be used), instantiated and then
                its state dict will be extracted.

            init_from_ptl_ckpt: Str name of a Pytorch Lightning checkpoint file. It will be loaded and
                the state dict will extracted.

        Args:
            cfg: The config used to instantiate the model. It need only contain one of the above keys.
            map_location: str or torch.device() which represents where the intermediate state dict
                (from the pretrained model or checkpoint) will be loaded.

        """
        args = ['init_from_nemo_model', 'init_from_pretrained_model', 'init_from_ptl_ckpt']
        arg_matches = [(1 if arg in cfg and arg is not None else 0) for arg in args]

        if sum(arg_matches) == 0:
            # model weights do not need to be restored
            return

        if sum(arg_matches) > 1:
            raise ValueError(
                f"Cannot pass more than one model initialization arguments to config!\n"
                f"Found : {[args[idx] for idx, arg_present in enumerate(arg_matches) if arg_present]}"
            )

        if 'init_from_nemo_model' in cfg and cfg.init_from_nemo_model is not None:
            with open_dict(cfg):
                # Restore model
                model_path = cfg.pop('init_from_nemo_model')
                restored_model = self.restore_from(model_path, map_location=map_location, strict=True)

                # Restore checkpoint into current model
                self.load_state_dict(restored_model.state_dict(), strict=False)
                logging.info(f'Model checkpoint restored from nemo file with path : `{model_path}`')

                del restored_model

        if 'init_from_pretrained_model' in cfg and cfg.init_from_pretrained_model is not None:
            with open_dict(cfg):
                # Restore model
                model_name = cfg.pop('init_from_pretrained_model')

                # Check if model is being resumed or not - only works if `Trainer` is attached to model
                if hasattr(self, 'trainer') and self.trainer is not None:
                    trainer = self.trainer
                    if (
                        hasattr(trainer, 'resume_from_checkpoint')
                        and trainer.checkpoint_connector.resume_checkpoint_path is not None
                    ):
                        logging.info(
                            "Model training is being resumed via Pytorch Lightning.\n"
                            "Initialization from pretrained model (via cloud) will be skipped."
                        )
                        return

                restored_model = self.from_pretrained(model_name, map_location=map_location, strict=True)

                # Restore checkpoint into current model
                self.load_state_dict(restored_model.state_dict(), strict=False)
                logging.info(f'Model checkpoint restored from pretrained chackpoint with name : `{model_name}`')

                del restored_model

        if 'init_from_ptl_ckpt' in cfg and cfg.init_from_ptl_ckpt is not None:
            with open_dict(cfg):
                # Restore checkpoint
                ckpt_path = cfg.pop('init_from_ptl_ckpt')
                ckpt = torch.load(ckpt_path, map_location=map_location)

                # Restore checkpoint into current model
                self.load_state_dict(ckpt['state_dict'], strict=False)
                logging.info(f'Model checkpoint restored from pytorch lightning chackpoint with path : `{ckpt_path}`')

                del ckpt

    def teardown(self, stage: str):
        """
        Called at the end of fit and test.

        Args:
            stage: either 'fit' or 'test'
        """
        if stage == 'fit':
            # Update env variable to bypass multi gpu issue after training
            # This fix affects usage of trainer.test() after trainer.train()
            # If trainer.train() was done on multiple GPUs, then trainer.test()
            # will try to do ddp, even if its a new Trainer object with just 1 GPU.
            # Temporary patch to fix that
            if 'PL_TRAINER_GPUS' in os.environ:
                os.environ.pop('PL_TRAINER_GPUS')

        super().teardown(stage)

    @classmethod
    def extract_state_dict_from(
        cls,
        restore_path: str,
        save_dir: str,
        split_by_module: bool = False,
        save_restore_connector: SaveRestoreConnector = None,
    ):
        """
        Extract the state dict(s) from a provided .nemo tarfile and save it to a directory.

        Args:
            restore_path: path to .nemo file from which state dict(s) should be extracted
            save_dir: directory in which the saved state dict(s) should be stored
            split_by_module: bool flag, which determins whether the output checkpoint should
                be for the entire Model, or the individual module's that comprise the Model
            save_restore_connector (SaveRestoreConnector): Can be overrided to add custom save and restore logic.

        Example:
            To convert the .nemo tarfile into a single Model level PyTorch checkpoint
            ::
            state_dict = nemo.collections.asr.models.EncDecCTCModel.extract_state_dict_from('asr.nemo', './asr_ckpts')


            To restore a model from a Model level checkpoint
            ::
            model = nemo.collections.asr.models.EncDecCTCModel(cfg)  # or any other method of restoration
            model.load_state_dict(torch.load("./asr_ckpts/model_weights.ckpt"))


            To convert the .nemo tarfile into multiple Module level PyTorch checkpoints
            ::
            state_dict = nemo.collections.asr.models.EncDecCTCModel.extract_state_dict_from('asr.nemo', './asr_ckpts', split_by_module=True)


            To restore a module from a Module level checkpoint
            ::
            model = nemo.collections.asr.models.EncDecCTCModel(cfg)  # or any other method of restoration

            # load the individual components
            model.preprocessor.load_state_dict(torch.load("./asr_ckpts/preprocessor.ckpt"))
            model.encoder.load_state_dict(torch.load("./asr_ckpts/encoder.ckpt"))
            model.decoder.load_state_dict(torch.load("./asr_ckpts/decoder.ckpt"))


        Returns:
            The state dict that was loaded from the original .nemo checkpoint
        """
        if save_restore_connector is None:
            save_restore_connector = SaveRestoreConnector()

        if not path.exists(restore_path):
            raise FileExistsError(f"Can't find {restore_path}")

        cls.update_save_restore_connector(save_restore_connector)
        state_dict = cls._save_restore_connector.extract_state_dict_from(restore_path, save_dir, split_by_module)
        return state_dict

    def prepare_test(self, trainer: 'Trainer') -> bool:
        """
        Helper method to check whether the model can safely be tested
        on a dataset after training (or loading a checkpoint).

        ::

            trainer = Trainer()
            if model.prepare_test(trainer):
                trainer.test(model)

        Returns:
            bool which declares the model safe to test. Provides warnings if it has to
            return False to guide the user.
        """
        if not hasattr(self._cfg, 'test_ds'):
            logging.info("No `test_ds` config found within the manifest.")
            return False

        # Replace ddp multi-gpu until PTL has a fix
        DDP_WARN = """\n\nDuring testing, it is currently advisable to construct a new Trainer "
                    "with single GPU and no DDP to obtain accurate results.
                    "Following pattern should be used: "
                    "gpu = 1 if cfg.trainer.gpus != 0 else 0"
                    "trainer = Trainer(gpus=gpu)"
                    "if model.prepare_test(trainer):"
                    "  trainer.test(model)\n\n"""

        if trainer is not None:
            if trainer.num_gpus > 1:
                logging.warning(DDP_WARN)
                return False

        # Assign trainer to the model
        self.set_trainer(trainer)
        return True

    def set_trainer(self, trainer: Trainer):
        """
        Set an instance of Trainer object.

        Args:
            trainer: PyTorch Lightning Trainer object.
        """
        self.trainer = trainer
        self._trainer = trainer
        self.set_world_size(self._trainer)

    def set_world_size(self, trainer: Trainer):
        """
        Determines the world size from the PyTorch Lightning Trainer.
        And then updates AppState.

        Args:
            trainer (Trainer): PyTorch Lightning Trainer object
        """
        # Update AppState with world information from trainer
        if isinstance(trainer, Trainer):
            app_state = AppState()
            if self._trainer.num_gpus and self._trainer.num_nodes:
                app_state.world_size = self._trainer.num_gpus * self._trainer.num_nodes
        else:
            logging.warning(f'World size can only be set by PyTorch Lightning Trainer.')

    def _update_dataset_config(self, dataset_name: str, config: Optional[Union[DictConfig, Dict]]):
        """
        Update the config (if not None) of the dataset by given name.
        Preserves said config after updating.

        Args:
            dataset_name: str name of the dataset whose config is being updated.
                Can be one of `train`, `validation` and `test`.
            config: Optional DictConfig or dict. If None is passed, this method simply returns.
                If dict is passed, it is cast into a DictConfig.
                The internal config is updated with the passed config.
        """
        if hasattr(self, '_multi_dataset_mode') and self._multi_dataset_mode is True:
            return

        if config is not None:
            if not isinstance(config, DictConfig):
                config = OmegaConf.create(config)

            if dataset_name in ['train', 'validation', 'test']:
                OmegaConf.set_struct(self.cfg, False)

                key_name = dataset_name + "_ds"
                self.cfg[key_name] = config

                OmegaConf.set_struct(self.cfg, True)

                # Update hyper parameters by calling property setter
                self.cfg = self._cfg
            else:
                raise ValueError("`dataset_name` when updating config must be one of [train, validation, test]")

    @property
    def num_weights(self):
        """
        Utility property that returns the total number of parameters of the Model.
        """
        num: int = 0
        for p in self.parameters():
            if p.requires_grad:
                num += p.numel()
        return num

    @property
    def cfg(self):
        """
        Property that holds the finalized internal config of the model.

        Note:
            Changes to this config are not reflected in the state of the model.
            Please create a new model using an updated config to properly update the model.
        """
        return self._cfg

    @cfg.setter
    def cfg(self, cfg):
        """
        Property that holds the finalized internal config of the model.

        Note:
            Changes to this config are not reflected in the state of the model.
            Please create a new model using an updated config to properly update the model.
        """
        self._cfg = cfg
        self._set_hparams(self._cfg)
        self._hparams_initial = copy.deepcopy(self._hparams)

    @staticmethod
    def _is_model_being_restored() -> bool:
        app_state = AppState()
        return app_state.is_model_being_restored

    @staticmethod
    def _set_model_restore_state(is_being_restored: bool, folder: str = None):
        app_state = AppState()
        app_state.is_model_being_restored = is_being_restored
        app_state.nemo_file_folder = folder

    def _set_model_guid(self):
        if not hasattr(self, 'model_guid'):
            appstate = AppState()

            # Generate a unique uuid for the instance
            # also determine if the model is being restored or not, and preserve the path
            self.model_guid = str(uuid.uuid4())
            if self._is_model_being_restored():
                restore_path = appstate.model_restore_path
            else:
                restore_path = None

            appstate.register_model_guid(self.model_guid, restoration_path=restore_path)

    @classmethod
    def update_save_restore_connector(cls, save_restore_connector):
        if hasattr(cls, '_save_restore_connector'):
            cls._save_restore_connector = save_restore_connector
        else:
            setattr(cls, '_save_restore_connector', save_restore_connector)