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Pytorch-lightning

The Keras for ML-research in Pytorch. Simple to use, but not as abstracted out.

Usage

To use lightning, first define a trainer function:

# trainer.py

from pytorch_lightning.models.trainer import Trainer   
from pytorch_lightning.utils.pt_callbacks import EarlyStopping, ModelCheckpoint
from my_project import My_Model   

# --------------------
# CALLBACKS
early_stop = EarlyStopping(
    monitor='val_loss',
    patience=3,
    verbose=True,
    mode='min'
)

model_save_path = 'PATH/TO/SAVE'
checkpoint = ModelCheckpoint(
    filepath=model_save_path,
    save_function=None,
    save_best_only=True,
    verbose=True,
    monitor='val_acc',
    mode='min'
)

# configure trainer
trainer = Trainer(
    on_gpu=False,
    enable_tqdm=True,
    overfit_pct=None,
    track_grad_norm=-1,
    fast_dev_run=False,
    check_val_every_n_epoch=1,
    accumulate_grad_batches=2,
    process_position=0,
    current_gpu_name=0,
    checkpoint_callback=checkpoint,
    early_stop_callback=early_stop,
    enable_early_stop=True,
    max_nb_epochs=12,
    min_nb_epochs=2,
    train_percent_check=1.0,
    val_percent_check=0.5,
    test_percent_check=0.5,
    val_check_interval=0.95,
    log_save_interval=0.95,
    add_log_row_interval=20,
    lr_scheduler_milestones=None
)

next define a model that implements these 10 functions:

import torch.nn as nn

class ExampleModel(RootModule):
    def __init__(self):
        # define model
    
    # ---------------
    # TRAINING
    def training_step(self, data_batch):
        x, y = data_batch
        y_hat = self.l1(x)
        loss = some_loss(y_hat)
        
        return loss_val, {'train_loss': loss}
    
    def validation_step(self, data_batch):
        x, y = data_batch
        y_hat = self.l1(x)
        loss = some_loss(y_hat)
        
        return loss_val, {'val_loss': loss}
 
     def validation_end(self, outputs):
        total_accs = []
        
        for output in outputs:
            total_accs.append(output['val_acc'].item())
        
        # return a dict
        return {'total_acc': np.mean(total_accs)}
     
     # ---------------
     # SAVING
     def get_save_dict(self):
        # lightning saves for you. Here's your chance to say what you want to save
        checkpoint = {'state_dict': self.state_dict()}

        return checkpoint

    def load_model_specific(self, checkpoint):
        # lightning loads for you. Here's your chance to say what you want to load
        self.load_state_dict(checkpoint['state_dict'])
    
    # ---------------
    # TRAINING CONFIG
    def configure_optimizers(self):
        # give lightning the list of optimizers you want to use.
        # lightning will call automatically
        optimizer = self.choose_optimizer('adam', self.parameters(), {'lr': self.hparams.learning_rate}, 'optimizer')
        return [optimizer]
    
    @property
    def tng_dataloader(self):
        return pytorch_dataloader('train')

    @property
    def val_dataloader(self):
        return pytorch_dataloader('val')

    @property
    def test_dataloader(self):
        return pytorch_dataloader('test')
        
    # ---------------
    # MODIFY YOUR COMMAND LINE ARGS
    @staticmethod
    def add_model_specific_args(parent_parser):    
        parser = HyperOptArgumentParser(strategy=parent_parser.strategy, parents=[parent_parser])
        parser.add_argument('--out_features', default=20)
        return parser

Details

Model definition

Name	Description	Input	Return
training_step	Called with a batch of data during training	data from your dataloaders	tuple: scalar, dict
validation_step	Called with a batch of data during validation	data from your dataloaders	tuple: scalar, dict
validation_end	Collate metrics from all validation steps	outputs: array where each item is the output of a validation step	dict: for logging
get_save_dict	called when your model needs to be saved (checkpoints, hpc save, etc...)	None	dict to be saved

Model training

Name	Description	Input	Return
configure_optimizers	called during training setup	None	list: optimizers you want to use
tng_dataloader	called during training	None	pytorch dataloader
val_dataloader	called during validation	None	pytorch dataloader
test_dataloader	called during testing	None	pytorch dataloader
add_model_specific_args	called with args you defined in your main. This lets you tailor args for each model and keep main the same	argparse	argparse

Model Saving/Loading

Name	Description	Input	Return
get_save_dict	called when your model needs to be saved (checkpoints, hpc save, etc...)	None	dict to be saved
load_model_specific	called when loading a model	checkpoint: dict you created in get_save_dict	dict: modified in whatever way you want

Add new model

Create a new model under /models.
Add model name to trainer_main

AVAILABLE_MODELS = {
    'model_1': ExampleModel1
}

Model methods that can be implemented

Method	Purpose	Input	Output	Required
forward()	Forward pass	model_in tuple with your data	model_out tuple to be passed to loss	Y
loss()	calculate model loss	model_out tuple from forward()	A scalar	Y
check_performance()	run a full loop through val data to check for metrics	dataloader, nb_tests	metrics tuple to be tracked	Y
tng_dataloader	Computed option, used to feed tng data	-	Pytorch DataLoader subclass	Y
val_dataloader	Computed option, used to feed tng data	-	Pytorch DataLoader subclass	Y
test_dataloader	Computed option, used to feed tng data	-	Pytorch DataLoader subclass	Y

Model lifecycle hooks

Use these hooks to customize functionality

Method	Purpose	Input	Output	Required
on_batch_start()	called right before the batch starts	-	-	N
on_batch_end()	called right after the batch ends	-	-	N
on_epoch_start()	called right before the epoch starts	-	-	N
on_epoch_end()	called right afger the epoch ends	-	-	N
on_pre_performance_check()	called right before the performance check starts	-	-	N
on_post_performance_check()	called right after the batch starts	-	-	N

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