NNx

Lightweight PyTorch training / eval / visualization toolkit, with first-class support for graph neural networks (GCN / GraphSAGE / GAT). Originally extracted from thekaveh/ml to underpin training loops, checkpointing, and result visualization across notebook-based experiments; now standalone.

1. Why NNx

If you've ever found yourself rewriting the same training loop, the same checkpoint shuffling, and the same metric plotting from project to project, that's NNx's purpose: a tight, opinionated layer that owns the boring parts so you can focus on the model.

1.1. Core capabilities

• Generic training loop — callbacks, early stopping, schedulers, AMP, gradient clipping, gradient accumulation, and seeded reproducibility.
• Content-addressed checkpoint management — FIRST / Q1 / Q2 / Q3 / LAST / BEST tags and a runs/best symlink that always points at your lowest-error run (lowest-loss for paradigm runs without a supervised error).
• Warm-resume training — load weights AND optimizer state from any saved checkpoint.
• Custom metrics injection — plug in any callable(Y_true, Y_pred) -> float via NNTrainParams.extra_metrics.
• TensorBoard and Weights & Biases callbacks — opt-in via extras.
• ONNX export — NNModel.to_onnx(path, example_input) with a single method call. Defaults to the legacy torch.onnx.export path (no extra deps); pass dynamo=True (with thekaveh-nnx[onnx-dynamo] installed) to use PyTorch's newer torch.export-based exporter.

1.2. Specializations

• Fine-tuning (transfer learning) — glob-pattern layer freezing, external state-dict loading, per-layer-group learning rates.
• Parameter-efficient fine-tuning (PEFT) — LoRA + DoRA + IA3 + Prefix-Tuning + Prompt-Tuning + Adapters. Per-method save_*_weights / load_*_weights persist only the trainable delta.
• Multi-optimizer Trainer — parallel to NNModel.train() for GAN / actor-critic workflows with a name-keyed dict of optimizers scoped via NNParamGroupSpec.
• Quantization — PTQ INT8 weight-only (quantize_int8) and QAT 8da4w (qat_train_step_factory + QATLifecycleCallback) via torchao.
• Pruning — magnitude unstructured (checkpoint-safe) and 2:4 semi-structured via torchao.
• Model surgery — widen / deepen (function-preserving Net2Net), drop_layer, low_rank_factorize (SVD), expand_embedding.
• Diffusion (DDPM) — noise-prediction training and reverse-diffusion sampling.
• Training paradigms — knowledge distillation (Hinton + FitNets-style feature-KD), contrastive (SimCLR / NT-Xent), Mixup, CutMix, sparse top-k Mixture-of-Experts (MoELinear + Switch-style aux loss), I-JEPA self-supervised pretraining, DPO preference fine-tuning, Born-Again iterated self-distillation.
• Language modeling — TransformerNN (decoder-only: RMSNorm + RoPE + SwiGLU + KV-cache) + NNTransformerParams + NNTokenizerParams + GenerativeNNModel.generate() with greedy / top-k / top-p / repetition-penalty sampling.
• Embeddings + FAISS — contrastive text-embedder training + FAISS index export for downstream RAG.
• GGUF + Ollama export — write a .gguf for the llama.cpp / Ollama / LM Studio ecosystem, including the Ollama Modelfile bundle.
• HuggingFace Hub — save_pretrained / push_to_hub / from_pretrained on NNModel via the PyTorchModelHubMixin, plus safetensors checkpoint format.
• Model-internals visualization — nnx.viz.summary (torchinfo) + weight_histogram + activation_map + attribute (Captum) + gradient_flow (per-layer gradient-norm diagnostic) + netron_export.
• Training-loop diagnostics — nnx.lr_finder(model, train_loader, *, loss_fn, ...) returns the Smith-2017 suggested one-cycle max_lr plus a Plotly figure; non-destructive (model state + training-mode restored on exit).
• Type-checked downstream — PEP 561 py.typed marker so consumers' pyright / mypy honor the public-surface annotations.

2. Where to next

2.1. Get running

• Quickstart — five minutes to a trained model, paste-runnable.

2.2. Understand the design

• Concepts — what an NNRun is, where things land on disk, how the enum-as-factory pattern works, how the twelve specialization subpackages compose.

2.3. Deep-dive guides

• Language modeling — train a tiny TransformerNN end-to-end (CPU-friendly).
• Direct Preference Optimization — fine-tune an LM on (prompt, chosen, rejected) preference pairs.
• I-JEPA — masked-patch latent-prediction self-supervised pretraining.
• Model surgery — function-preserving Net2Net + low-rank + drop primitives.
• Embeddings + FAISS — contrastive training + RAG-ready export.
• HuggingFace Hub — safetensors + Hub publish/load.
• GGUF & Ollama — export to llama.cpp ecosystem.
• Comparison vs Lightning / HF / fastai / Composer — scope-explicit decision matrix for picking the right PyTorch training toolkit.

2.4. Look things up

• API Reference — auto-generated from docstrings (sections 1–20).
• Examples catalog — annotated index of the runnable scripts under examples/.
• CONTRIBUTING — editable install, dev toolchain, PR workflow.
• CHANGELOG — user-visible changes per PR.

3. Status

Alpha. API is stable for the existing thekaveh/ml notebook consumer; pre-1.0 means we'll fix bugs (see CHANGELOG) without renaming public APIs unless they're broken in ways notebooks can't work around.