ai-ml-expert（AI 机器学习专家）

AI/ML Expert

Core Framework Guidelines

PyTorch

When reviewing or writing PyTorch code, apply these guidelines:

• Use torch.nn.Module for all model definitions; avoid raw function-based models
• Move tensors and models to the correct device explicitly: model.to(device), tensor.to(device)
• Use model.train() and model.eval() context switches appropriately
• Accumulate gradients with optimizer.zero_grad() at the top of the training loop
• Use torch.no_grad() or @torch.inference_mode() for all inference code
• Pin memory (pin_memory=True) and use multiple workers in DataLoader for GPU training
• Use torch.compile() (PyTorch 2.x) for production inference speedups
• Prefer F.cross_entropy over manual softmax + NLLLoss (numerically stable)

TensorFlow / Keras

When reviewing or writing TensorFlow code, apply these guidelines:

• Use the Keras functional API or subclassing API; avoid Sequential for complex models
• Prefer tf.data.Dataset pipelines over manual batching for scalability
• Use tf.function for graph execution on performance-critical paths
• Apply mixed precision training: tf.keras.mixed_precision.set_global_policy('mixed_float16')
• Use tf.saved_model for portable model export; avoid pickling

Hugging Face Transformers

When reviewing or writing Hugging Face code, apply these guidelines:

• Always use the tokenizer associated with the model checkpoint
• Set padding=True and truncation=True when tokenizing batches
• Use AutoModel, AutoTokenizer, and AutoConfig for checkpoint portability
• Apply model.gradient_checkpointing_enable() to reduce memory for large models
• Use Trainer API for standard fine-tuning; use custom loops only when Trainer is insufficient
• Cache models with TRANSFORMERS_CACHE environment variable in CI/CD pipelines

scikit-learn

When reviewing or writing scikit-learn code, apply these guidelines:

• Use Pipeline to chain preprocessing and model steps; prevents data leakage
• Use StratifiedKFold for classification tasks with class imbalance
• Prefer GridSearchCV or RandomizedSearchCV for hyperparameter tuning
• Always call .fit() only on training data; transform test data with the fitted transformer
• Serialize models with joblib.dump / joblib.load (faster than pickle for large arrays)

LLM Integration Patterns

Prompt Engineering

• Structure prompts with a clear system message, context, and user instruction
• Use few-shot examples in the system prompt for consistent output formatting
• Apply chain-of-thought prompting ("Think step by step...") for complex reasoning tasks
• Set temperature=0 for deterministic, fact-based outputs; increase for creative tasks
• Manage token budgets explicitly: estimate prompt tokens before sending
• Implement output parsing with structured formats (JSON mode, XML tags)

RAG Pipelines

# Standard RAG pipeline components
from langchain.embeddings import HuggingFaceEmbeddings
from langchain.vectorstores import FAISS  # or Chroma, Pinecone, Weaviate
from langchain.chains import RetrievalQA

# 1. Embed and index documents
embeddings = HuggingFaceEmbeddings(model_name="sentence-transformers/all-mpnet-base-v2")
vectorstore = FAISS.from_documents(documents, embeddings)

# 2. Retrieve relevant chunks
retriever = vectorstore.as_retriever(search_kwargs={"k": 4})

# 3. Generate with retrieved context
chain = RetrievalQA.from_chain_type(llm=llm, retriever=retriever)

RAG best practices:

• Chunk documents at natural boundaries (paragraphs, sections), not fixed character counts
• Use hybrid retrieval: combine dense embeddings with sparse BM25 for better recall
• Implement semantic caching for repeated queries to reduce latency and cost
• Validate retrieved context relevance before passing to the LLM
• Store metadata alongside embeddings for filtering (date, source, author)

LangChain / LangGraph

• Use LCEL (LangChain Expression Language) for composable chains
• Apply RunnableParallel for concurrent retrieval steps
• Use LangGraph for stateful multi-agent workflows with cycles
• Implement retry logic with RunnableRetry for unreliable external calls
• Trace and evaluate chains with LangSmith in development

Training Loop Standards

# Standard PyTorch training loop with best practices
for epoch in range(num_epochs):
    model.train()
    for batch in train_dataloader:
        optimizer.zero_grad()
        inputs, labels = batch["input_ids"].to(device), batch["labels"].to(device)
        outputs = model(inputs)
        loss = criterion(outputs, labels)
        loss.backward()
        torch.nn.utils.clip_grad_norm_(model.parameters(), max_norm=1.0)  # gradient clipping
        optimizer.step()
        scheduler.step()

    # Validation loop
    model.eval()
    with torch.no_grad():
        for batch in val_dataloader:
            # evaluate...

Key standards:

• Proper train/validation/test splits: 80/10/10 or stratified for imbalanced datasets
• Gradient clipping (max_norm=1.0) for stability in Transformer training
• Learning rate scheduling: cosine annealing with warmup for Transformers
• Early stopping based on validation loss, not training loss
• Checkpoint the best model by validation metric, not the final epoch

Fine-Tuning Standards

Full Fine-Tuning

• Reduce learning rate 10-100x compared to training from scratch
• Freeze early layers; fine-tune upper layers and task head first
• Use discriminative learning rates: lower LR for frozen layers, higher for new layers
• Apply label smoothing (smoothing=0.1) to reduce overconfidence

Parameter-Efficient Fine-Tuning (PEFT)

from peft import LoraConfig, get_peft_model, TaskType

lora_config = LoraConfig(
    task_type=TaskType.CAUSAL_LM,
    r=16,               # LoRA rank
    lora_alpha=32,      # scaling factor
    target_modules=["q_proj", "v_proj"],
    lora_dropout=0.05,
)
model = get_peft_model(base_model, lora_config)
model.print_trainable_parameters()  # verify < 1% parameters trainable

PEFT guidelines:

• Use LoRA rank r=8 to r=64; higher rank = more capacity, more memory
• QLoRA (4-bit quantization + LoRA) for fine-tuning 7B+ models on consumer GPUs
• Merge adapter weights before serving to eliminate inference overhead
• Prefer adapter-based methods over full fine-tuning for limited data (< 10K examples)

MLOps and Experiment Tracking

MLflow

import mlflow

with mlflow.start_run():
    mlflow.log_params({"learning_rate": lr, "batch_size": bs, "epochs": epochs})
    mlflow.log_metrics({"train_loss": loss, "val_accuracy": acc}, step=epoch)
    mlflow.pytorch.log_model(model, "model")

Weights & Biases

import wandb

wandb.init(project="my-project", config={"lr": 1e-4, "epochs": 10})
wandb.log({"train_loss": loss, "val_f1": f1_score})
wandb.finish()

MLOps standards:

• Log every hyperparameter and dataset version before training starts
• Track system metrics (GPU utilization, memory, throughput) alongside model metrics
• Version datasets with DVC or Delta Lake; never overwrite raw data
• Use reproducible seeds: torch.manual_seed(42), np.random.seed(42), random.seed(42)
• Register production models in a model registry with stage gates (Staging → Production)

Model Evaluation Standards

Metrics by Task Type

Evaluation Best Practices

• Never tune hyperparameters on the test set; use a held-out validation set
• Report confidence intervals (bootstrap or cross-validation) for all metrics
• Disaggregate metrics by subgroup for fairness analysis
• Use statistical significance tests (McNemar, paired t-test) when comparing models
• Establish a simple baseline before reporting model results

Production ML Systems

Model Deployment

• Export to ONNX for cross-platform inference: torch.onnx.export(model,...)
• Use TorchServe, Triton Inference Server, or BentoML for serving
• Apply quantization for CPU deployment: torch.quantization.quantize_dynamic(model,...)
• Set up batching with a maximum batch size and timeout for throughput vs latency tradeoffs
• Use model warming (pre-load and dummy inference) to eliminate cold-start latency

Monitoring and Drift Detection

# Example: data drift detection with Evidently
from evidently.report import Report
from evidently.metric_preset import DataDriftPreset

report = Report(metrics=[DataDriftPreset()])
report.run(reference_data=reference_df, current_data=production_df)
report.save_html("drift_report.html")

Monitoring standards:

• Track feature distribution drift (KS test, PSI) on a daily schedule
• Alert on prediction distribution shift (concept drift)
• Log and sample model inputs/outputs for downstream evaluation
• Implement shadow mode (run new model alongside production, compare outputs)
• Define retraining triggers based on drift thresholds, not fixed schedules

Data Preprocessing Standards

# Proper train/test split to avoid leakage
from sklearn.model_selection import train_test_split

X_train, X_test, y_train, y_test = train_test_split(
    X, y, test_size=0.2, random_state=42, stratify=y  # stratify for classification
)

# Fit scaler ONLY on training data
from sklearn.preprocessing import StandardScaler
scaler = StandardScaler()
X_train_scaled = scaler.fit_transform(X_train)
X_test_scaled = scaler.transform(X_test)  # transform only, never fit_transform

Standards:

• Separate preprocessing pipeline per data modality (text, image, tabular)
• Validate schema and types before entering the pipeline
• Handle missing values with domain-aware strategies (median, mode, forward-fill)
• Detect and document outliers; do not silently remove them
• Apply augmentation only to training data, never validation or test data

Iron Laws

1. ALWAYS fix random seeds and log all hyperparameters before training — non-reproducible experiments cannot be shared, audited, or debugged; use torch.manual_seed(42), np.random.seed(42), random.seed(42) and log via MLflow/W&B.
2. NEVER fit preprocessing transformers on test data — fit only on training data, then .transform() test; fitting on test causes data leakage and inflated performance estimates.
3. ALWAYS evaluate with multiple metrics aligned to business goals — never report accuracy alone on imbalanced datasets; use F1, precision-recall curve, and ROC-AUC at minimum.
4. NEVER tune hyperparameters on the test set — use a held-out validation set for tuning; the test set is a one-time final evaluation only.
5. ALWAYS establish a simple baseline before reporting model results — a heuristic or random baseline is mandatory; without it, model quality cannot be assessed.

Anti-Patterns

Training a Transformer classifier:

from transformers import AutoTokenizer, AutoModelForSequenceClassification, Trainer, TrainingArguments

tokenizer = AutoTokenizer.from_pretrained("distilbert-base-uncased")
model = AutoModelForSequenceClassification.from_pretrained("distilbert-base-uncased", num_labels=3)

def tokenize(batch):
    return tokenizer(batch["text"], padding=True, truncation=True, max_length=512)

dataset = dataset.map(tokenize, batched=True)

training_args = TrainingArguments(
    output_dir="./results",
    num_train_epochs=3,
    per_device_train_batch_size=16,
    evaluation_strategy="epoch",
    save_strategy="epoch",
    load_best_model_at_end=True,
    metric_for_best_model="f1",
)

trainer = Trainer(
    model=model,
    args=training_args,
    train_dataset=dataset["train"],
    eval_dataset=dataset["validation"],
    compute_metrics=compute_metrics,
)
trainer.train()

Minimal RAG pipeline:

from langchain.embeddings import OpenAIEmbeddings
from langchain.vectorstores import Chroma
from langchain.chains import RetrievalQA
from langchain.chat_models import ChatOpenAI

vectorstore = Chroma.from_documents(docs, OpenAIEmbeddings())
retriever = vectorstore.as_retriever(search_kwargs={"k": 5})
qa = RetrievalQA.from_chain_type(ChatOpenAI(model="gpt-4o"), retriever=retriever)
answer = qa.run("What is the refund policy?")

Assigned Agents

This skill is used by:

• developer — Implements ML models, data pipelines, and LLM integrations
• researcher — Investigates novel architectures and evaluates research papers
• architect — Designs ML system architecture and deployment topology
• security-architect — Reviews data privacy, model security, and inference safety

Related Skills

• python-backend-expert — NumPy, Pandas, async Python patterns
• code-analyzer — Static analysis and complexity metrics for ML code
• debugging — Systematic debugging for training failures and inference errors

Memory Protocol (MANDATORY)

Before starting:

cat .claude/context/memory/learnings.md

Check for:

• Previously solved ML patterns in this codebase
• Known library version pinning requirements
• Infrastructure constraints (GPU type, memory limits)

After completing:

• New ML pattern or fix → .claude/context/memory/learnings.md
• Training failure root cause → .claude/context/memory/issues.md
• Architecture decision (framework choice, deployment strategy) → .claude/context/memory/decisions.md

ASSUME INTERRUPTION: Your context may reset. If it's not in memory, it didn't happen.