MLOps Coding - Productionizing Skill

Goal

To convert experimental code (notebooks/scripts) into a high-quality, distributable Python package. This skill enforces the src/ layout, a Hybrid Paradigm (OOP structure + Functional purity), and Strict Configuration to ensure scalability, security, and maintainability.

Prerequisites

• Language: Python
• Manager: uv
• Context: Moving from notebooks/ to src/.

Instructions

1. Packaging Structure (src Layout)

Adopt the src layout to prevent import errors and separate source from tooling.

1. Directory Tree:

   my-project/
   ├── pyproject.toml       # Dependencies & Metadata
   ├── uv.lock
   ├── README.md
   └── src/
       └── my_package/      # Main package directory
           ├── __init__.py
           ├── io/          # Side-effects (Datasets, APIs)
           ├── domain/      # Pure business logic (Models, Features)
           └── application/ # Orchestration (Training loops, Inference)

2. Configuration: Use pyproject.toml for all build metadata and dependencies.

2. Modularity & Paradigm (Hybrid Style)

Balance structure with predictability.

1. Domain Layer (Pure):
   • Rule: Code here must be deterministic and free of side effects (no I/O).
   • Use Case: Feature transformations, Model architecture definitions.
   • Style: Functional (pure functions) or Immutable Objects (dataclasses).
2. I/O Layer (Impure):
   • Rule: Isolate external interactions here.
   • Use Case: Loading data from S3, saving models to disk, logging to MLflow.
   • Style: OOP (Classes to manage connections/state).
3. Application Layer (Orchestration):
   • Rule: Wire Domain and I/O together.
   • Use Case: Tuning, Training, Inference, Evaluation, etc.

3. Application Entrypoints

Create standard, installable CLI tools.

1. Define Script: Create src/my_package/scripts.py with a main() function.

2. Register: Add to pyproject.toml:

   [project.scripts]
   my-tool = "my_package.scripts:main"

3. CLI Execution:

   • Dev: uv run my-tool (No install needed).
   • Prod: pip install . -> my-tool (Installed on PATH).

4. Guard: Always use if __name__ == "__main__": in scripts to prevent execution on import.

4. Configuration Management

Decouple settings from code using OmegaConf (Parsing) and Pydantic (Validation).

1. Define Schema (Pydantic):

   • Create a class that defines expected types and defaults.

   from pydantic import BaseModel
   
   class TrainingConfig(BaseModel):
       batch_size: int = 32
       learning_rate: float = 0.001
       use_gpu: bool = False

2. Parse & Validate (OmegaConf):

   • Load YAML, merge with CLI args, and validate against the schema.

   import omegaconf
   
   # 1. Load YAML
   conf = omegaconf.OmegaConf.load("config.yaml")
   # 2. Merge with CLI (optional)
   cli_conf = omegaconf.OmegaConf.from_cli()
   merged = omegaconf.OmegaConf.merge(conf, cli_conf)
   # 3. Validate -> Returns a validated Pydantic object
   cfg: TrainingConfig = TrainingConfig(**omegaconf.OmegaConf.to_container(merged))

3. Secrets: Use Environment Variables (os.getenv), never commit them.

5. Documentation & Quality

Make code usable and maintainable.

1. Docstrings: Use Google Style docstrings for all modules, classes, and functions.

   def calculate_metric(y_true: np.ndarray, y_pred: np.ndarray) -> float:
       """Calculates the accuracy score.
   
       Args:
           y_true: Ground truth labels.
           y_pred: Predicted labels.
   
       Returns:
           The accuracy as a float between 0 and 1.
       """

2. Type Hints: Use standard python typing (typing, list[str]) everywhere.

6. Best Practices Summary

• Config != Code: Never hardcode paths or hyperparams; use the Pydantic + OmegaConf pattern.
• Entrypoints are APIs: Design your CLI ([project.scripts]) as the public interface for your automation tools.
• Immutable Core: Keep your domain logic side-effect free; push I/O to the edges.

Self-Correction Checklist

• No Side Effects on Import: Does import my_package run any code? (It shouldn't).
• Src Layout: Is code inside src/?
• Config Safety: Are secrets excluded from pyproject.toml and YAML?
• Typing: Are function signatures fully type-hinted?
• Entrypoints: Is the CLI registered in pyproject.toml?