Pytorch-lightning

The Keras for ML-researchers in PyTorch.

Usage

To use lightning do 2 things:

1. Define a trainer (which will run ALL your models).
2. Define a model.

Example:

Define the trainer

# trainer.py

from pytorch_lightning.models.trainer import Trainer   
from pytorch_lightning.utils.pt_callbacks import EarlyStopping, ModelCheckpoint
from my_project import My_Model   
from test_tube import HyperOptArgumentParser, Experiment, SlurmCluster

# --------------
# TEST TUBE INIT
exp = Experiment(
    name='my_exp',
    debug=True,
    save_dir='/some/path',
    autosave=False,
    description='my desc'
)

# --------------------
# 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(
    experiment=experiment,
    cluster=cluster,
    checkpoint_callback=checkpoint,
    early_stop_callback=early_stop
)  

# init model and train
model = My_Model()
trainer.fit(model)

Define the model

from torch import nn

class My_Model(RootModule):
    def __init__(self):
        # define model
        self.l1 = nn.Linear(200, 10)
    
    # ---------------
    # 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

Optional model hooks.

Add these to the model whenever you want to configure training behavior.

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