Train a model (basic)¶
Audience: Users who need to train a model without coding their own training loops.
Add imports¶
Add the relevant imports at the top of the file
import os
import torch
from torch import nn
import torch.nn.functional as F
from torchvision import transforms
from torchvision.datasets import MNIST
from torch.utils.data import DataLoader, random_split
import pytorch_lightning as pl
Define the PyTorch nn.Modules¶
class Encoder(nn.Module):
def __init__(self):
super().__init__()
self.l1 = nn.Sequential(nn.Linear(28 * 28, 64), nn.ReLU(), nn.Linear(64, 3))
def forward(self, x):
return self.l1(x)
class Decoder(nn.Module):
def __init__(self):
super().__init__()
self.l1 = nn.Sequential(nn.Linear(3, 64), nn.ReLU(), nn.Linear(64, 28 * 28))
def forward(self, x):
return self.l1(x)
Define a LightningModule¶
The LightningModule is the full recipe that defines how your nn.Modules interact.
The training_step defines how the nn.Modules interact together.
In the configure_optimizers define the optimizer(s) for your models.
class LitAutoEncoder(pl.LightningModule):
def __init__(self, encoder, decoder):
super().__init__()
self.encoder = encoder
self.decoder = decoder
def training_step(self, batch, batch_idx):
# training_step defines the train loop.
x, y = batch
x = x.view(x.size(0), -1)
z = self.encoder(x)
x_hat = self.decoder(z)
loss = F.mse_loss(x_hat, x)
return loss
def configure_optimizers(self):
optimizer = torch.optim.Adam(self.parameters(), lr=1e-3)
return optimizer
Define the training dataset¶
Define a PyTorch DataLoader
which contains your training dataset.
dataset = MNIST(os.getcwd(), download=True, transform=transforms.ToTensor())
train_loader = DataLoader(dataset)
Train the model¶
To train the model use the Lightning Trainer which handles all the engineering and abstracts away all the complexity needed for scale.
# model
autoencoder = LitAutoEncoder(Encoder(), Decoder())
# train model
trainer = pl.Trainer()
trainer.fit(model=autoencoder, train_dataloaders=train_loader)
Eliminate the training loop¶
Under the hood, the Lightning Trainer runs the following training loop on your behalf
autoencoder = LitAutoEncoder(Encoder(), Decoder())
optimizer = autoencoder.configure_optimizers()
for batch_idx, batch in enumerate(train_loader):
loss = autoencoder.training_step(batch, batch_idx)
loss.backward()
optimizer.step()
optimizer.zero_grad()
The power of Lightning comes when the training loop gets complicated as you add validation/test splits, schedulers, distributed training and all the latest SOTA techniques.
With Lightning, you can add mix all these techniques together without needing to rewrite a new loop every time.