pytorch

Overview

PyTorch is a deep learning framework for building and training neural networks with dynamic computation graphs and automatic differentiation. It provides tensor operations with GPU acceleration, nn.Module for defining architectures, DataLoader for efficient data loading, mixed precision training for performance, and export tools (TorchScript, ONNX) for production deployment.

Instructions

• When defining models, subclass nn.Module with __init__ for layers and forward for computation, using nn.Sequential for simple stacks and custom forward logic for complex architectures.
• When training, implement the standard loop: forward pass, loss computation, loss.backward(), optimizer.step(), optimizer.zero_grad(), with gradient clipping via clip_grad_norm_ for stability.
• When loading data, subclass Dataset with __len__ and __getitem__, then use DataLoader with num_workers=4 and pin_memory=True for GPU training throughput.
• When optimizing performance, use torch.compile(model) on PyTorch 2.0+ for 20-50% speedup, mixed precision with torch.amp.autocast() for halved memory and doubled throughput, and DistributedDataParallel for multi-GPU training.
• When doing transfer learning, load pretrained models from torchvision.models or Hugging Face, freeze the backbone, and replace the classifier head for your task.
• When deploying, use torch.export() or torch.jit.trace() for production, torch.onnx.export() for cross-framework compatibility, and torch.quantization for INT8 inference speedup.

Examples

Example 1: Fine-tune a vision model for image classification

User request: "Fine-tune a pretrained ResNet for classifying product images"

Actions:

1. Load resnet50(weights=ResNet50_Weights.DEFAULT) and freeze all layers except the final classifier
2. Replace the classifier head with nn.Linear(2048, num_classes)
3. Set up DataLoader with image augmentation transforms (RandomCrop, ColorJitter, Normalize)
4. Train with AdamW, CosineAnnealingLR scheduler, and mixed precision

Output: A fine-tuned image classifier with production-quality accuracy and efficient mixed-precision training.

Example 2: Train a text classification model with Hugging Face

User request: "Build a sentiment analysis model using a pretrained transformer"

Actions:

1. Load AutoModel.from_pretrained("bert-base-uncased") with a classification head
2. Tokenize the dataset using AutoTokenizer and create a DataLoader
3. Fine-tune with AdamW, linear warmup scheduler, and gradient clipping
4. Export the trained model with torch.export() for production serving

Output: A sentiment analysis model fine-tuned on custom data and exported for production inference.

Guidelines

• Use torch.compile(model) on PyTorch 2.0+ for a free 20-50% speedup with one line.
• Use AdamW over Adam for correct weight decay implementation with modern architectures.
• Use mixed precision (torch.amp) for any GPU training to halve memory and double throughput.
• Move data to device in the training loop, not in the Dataset, to keep Dataset device-agnostic.
• Use model.eval() and torch.no_grad() during inference to prevent unnecessary gradient computation.
• Use pin_memory=True in DataLoader when training on GPU to speed up CPU-to-GPU data transfer.
• Save model.state_dict() not the full model since state dicts are portable across code changes.