What problem does it solve? Writing raw PyTorch training loops requires repetitive boilerplate for device management, distributed synchronization, checkpointing, and logging, which introduces bugs and slows down research iteration. ## Core Features & Use Cases - Structured Training Loops: Organize model code into a LightningModule with training_step, validation_step, and configure_optimizers while the Trainer handles devices, precision, and logging. - Automatic Distributed Training: Switch between DDP, FSDP, and DeepSpeed strategies with a single parameter, scaling from one GPU to multi-node clusters without code changes. - Callbacks and Tuning: Use ModelCheckpoint, EarlyStopping, and LearningRateMonitor callbacks, plus integrations with Ray Tune, Optuna, and WandB sweeps for hyperparameter search. - Use Case: Convert an existing PyTorch training script into a LightningModule, then launch 8-GPU DDP training with BF16 precision and automatic best-model checkpointing using one Trainer configuration. ## Quick Start Convert my PyTorch training loop into a PyTorch Lightning module and run it on multiple GPUs with DDP and early stopping.