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Use Lightning Apps to build everything from production-ready, multi-cloud ML systems to simple research demos.

Project description


The Deep Learning framework to train, deploy, and ship AI products Lightning fast.

NEW- Lightning 2.0 is featuring a clean and stable API!!

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Install Lightning

Simple installation from PyPI

pip install lightning

Lightning has 3 core packages

PyTorch Lightning: Train and deploy PyTorch at scale.
Lightning Fabric: Expert control.
Lightning Apps: Build AI products and ML workflows.

Lightning gives you granular control over how much abstraction you want to add over PyTorch.

PyTorch Lightning: Train and Deploy PyTorch at Scale

PyTorch Lightning is just organized PyTorch - Lightning disentangles PyTorch code to decouple the science from the engineering.

Hello simple model

# ! pip install torchvision
import os, torch, torch.nn as nn, as data, torchvision as tv, torch.nn.functional as F
import lightning as L

# --------------------------------
# Step 1: Define a LightningModule
# --------------------------------
# A LightningModule (nn.Module subclass) defines a full *system*
# (ie: an LLM, difussion model, autoencoder, or simple image classifier).

class LitAutoEncoder(L.LightningModule):
    def __init__(self):
        self.encoder = nn.Sequential(nn.Linear(28 * 28, 128), nn.ReLU(), nn.Linear(128, 3))
        self.decoder = nn.Sequential(nn.Linear(3, 128), nn.ReLU(), nn.Linear(128, 28 * 28))

    def forward(self, x):
        # in lightning, forward defines the prediction/inference actions
        embedding = self.encoder(x)
        return embedding

    def training_step(self, batch, batch_idx):
        # training_step defines the train loop. It is independent of forward
        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)
        self.log("train_loss", loss)
        return loss

    def configure_optimizers(self):
        optimizer = torch.optim.Adam(self.parameters(), lr=1e-3)
        return optimizer

# -------------------
# Step 2: Define data
# -------------------
dataset = tv.datasets.MNIST(os.getcwd(), download=True, transform=tv.transforms.ToTensor())
train, val = data.random_split(dataset, [55000, 5000])

# -------------------
# Step 3: Train
# -------------------
autoencoder = LitAutoEncoder()
trainer = L.Trainer(), data.DataLoader(train), data.DataLoader(val))

Run the model on your terminal

pip install torchvision

Advanced features

Lightning has over 40+ advanced features designed for professional AI research at scale.

Here are some examples:

Train on 1000s of GPUs without code changes
# 8 GPUs
# no code changes needed
trainer = Trainer(accelerator="gpu", devices=8)

# 256 GPUs
trainer = Trainer(accelerator="gpu", devices=8, num_nodes=32)
Train on other accelerators like TPUs without code changes
# no code changes needed
trainer = Trainer(accelerator="tpu", devices=8)
16-bit precision
# no code changes needed
trainer = Trainer(precision=16)
Experiment managers
from lightning import loggers

# tensorboard
trainer = Trainer(logger=TensorBoardLogger("logs/"))

# weights and biases
trainer = Trainer(logger=loggers.WandbLogger())

# comet
trainer = Trainer(logger=loggers.CometLogger())

# mlflow
trainer = Trainer(logger=loggers.MLFlowLogger())

# neptune
trainer = Trainer(logger=loggers.NeptuneLogger())

# ... and dozens more
Early Stopping
es = EarlyStopping(monitor="val_loss")
trainer = Trainer(callbacks=[es])
checkpointing = ModelCheckpoint(monitor="val_loss")
trainer = Trainer(callbacks=[checkpointing])
Export to torchscript (JIT) (production use)
# torchscript
autoencoder = LitAutoEncoder(), "")
Export to ONNX (production use)
# onnx
with tempfile.NamedTemporaryFile(suffix=".onnx", delete=False) as tmpfile:
    autoencoder = LitAutoEncoder()
    input_sample = torch.randn((1, 64))
    autoencoder.to_onnx(, input_sample, export_params=True)

Advantages over unstructured PyTorch

  • Models become hardware agnostic
  • Code is clear to read because engineering code is abstracted away
  • Easier to reproduce
  • Make fewer mistakes because lightning handles the tricky engineering
  • Keeps all the flexibility (LightningModules are still PyTorch modules), but removes a ton of boilerplate
  • Lightning has dozens of integrations with popular machine learning tools.
  • Tested rigorously with every new PR. We test every combination of PyTorch and Python supported versions, every OS, multi GPUs and even TPUs.
  • Minimal running speed overhead (about 300 ms per epoch compared with pure PyTorch).

Lightning Fabric: Expert control.

Run on any device at any scale with expert-level control over PyTorch training loop and scaling strategy. You can even write your own Trainer.

Fabric is designed for the most complex models like foundation model scaling, LLMs, diffussion, transformers, reinforcement learning, active learning.

+ import lightning as L
  import torch
  import torch.nn as nn
  from import DataLoader, Dataset
  class PyTorchModel(nn.Module):
  class PyTorchDataset(Dataset):
+ fabric = L.Fabric(accelerator="cuda", devices=8, strategy="ddp")
+ fabric.launch()
- device = "cuda" if torch.cuda.is_available() else "cpu
  model = PyTorchModel(...)
  optimizer = torch.optim.SGD(model.parameters())
+ model, optimizer = fabric.setup(model, optimizer)
  dataloader = DataLoader(PyTorchDataset(...), ...)
+ dataloader = fabric.setup_dataloaders(dataloader)
  for epoch in range(num_epochs):
      for batch in dataloader:
          input, target = batch
-         input, target =,
          output = model(input)
          loss = loss_fn(output, target)
-         loss.backward()
+         fabric.backward(loss)

Key features

  • Easily switch from running on CPU to GPU (Apple Silicon, CUDA, …), TPU, multi-GPU or even multi-node training
  • Use state-of-the-art distributed training strategies (DDP, FSDP, DeepSpeed) and mixed precision out of the box
  • All the device logic boilerplate is handled for you
  • Designed with multi-billion parameter models in mind
  • Build your own custom Trainer using Fabric primitives for training checkpointing, logging, and more

Lightning Apps: Build AI products and ML workflows

Lightning Apps remove the cloud infrastructure boilerplate so you can focus on solving the research or business problems. Lightning Apps can run on the Lightning Cloud, your own cluster or a private cloud.

Hello Lightning app world

import lightning as L

class TrainComponent(L.LightningWork):
    def run(self, x):
        print(f"train a model on {x}")

class AnalyzeComponent(L.LightningWork):
    def run(self, x):
        print(f"analyze model on {x}")

class WorkflowOrchestrator(L.LightningFlow):
    def __init__(self) -> None:
        self.train = TrainComponent(cloud_compute=L.CloudCompute("cpu"))
        self.analyze = AnalyzeComponent(cloud_compute=L.CloudCompute("gpu"))

    def run(self):"CPU machine 1")"GPU machine 2")

app = L.LightningApp(WorkflowOrchestrator())

Run on the cloud or locally

# run on the cloud
lightning run app --setup --cloud

# run locally
lightning run app


Self-supervised Learning
Convolutional Architectures
Reinforcement Learning
Classic ML

Continuous Integration

Lightning is rigorously tested across multiple CPUs, GPUs, TPUs, IPUs, and HPUs and against major Python and PyTorch versions.

*Codecov is > 90%+ but build delays may show less
Current build statuses <center>
System / PyTorch ver. 1.11 1.12 1.13 2.0
Linux py3.9 [GPUs] - Build Status Build Status Soon
Linux py3.9 [TPUs] - Test PyTorch - TPU Soon
Linux py3.8 [IPUs] - - Build Status Soon
Linux py3.8 [HPUs] - - Build Status Soon
Linux (multiple Python versions) Test PyTorch Test PyTorch Test PyTorch Soon
OSX (multiple Python versions) Test PyTorch Test PyTorch Test PyTorch Soon
Windows (multiple Python versions) Test PyTorch Test PyTorch Test PyTorch Soon


The lightning community is maintained by

  • 10+ core contributors who are all a mix of professional engineers, Research Scientists, and Ph.D. students from top AI labs.
  • 590+ active community contributors.

Want to help us build Lightning and reduce boilerplate for thousands of researchers? Learn how to make your first contribution here

Lightning is also part of the PyTorch ecosystem which requires projects to have solid testing, documentation and support.

Asking for help

If you have any questions please:

  1. Read the docs.
  2. Search through existing Discussions, or add a new question
  3. Join our discord.

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