python

name	python
description	Build maintainable Python backend and service code with strong typing, safe error handling, clean module boundaries, and testable workflows. Use for FastAPI services, data pipelines, and integration-heavy Python changes.

Python Skill

Use this skill for Python backend, service, and pipeline work.

When to apply

• FastAPI endpoint design and request/response contracts
• Service-layer refactors and orchestration logic
• Error handling and reliability hardening
• Data processing and integration workflows
• Type-driven cleanup and maintainability improvements

Workflow

1. Start from contracts.

• Define input/output schemas first.
• Keep transport models separate from business logic.

2. Keep modules focused.

• API routes: auth + validation + response mapping.
• Service layer: orchestration and domain rules.
• Data layer: storage/query concerns only.

3. Make failure modes explicit.

• Convert exceptions into actionable error responses.
• Add fallback behavior for external/model failures where needed.

4. Type and document critical paths.

• Add precise type hints on function boundaries.
• Keep complex behavior in small named functions.

5. Keep side effects controlled.

• Centralize environment/config access.
• Avoid hidden globals unless lifecycle is explicit.

6. Validate before ship.

• Run target tests/build checks.
• Confirm no regressions in endpoint contracts.

Patterns to prefer

• Pydantic models for API boundaries
• Service wrappers for orchestration flows
• Idempotent startup/init routines
• Structured logging around integration boundaries

Anti-patterns

• Endpoint handlers with embedded business logic
• Catch-all exceptions that hide root causes
• Implicit type conversions at runtime boundaries
• Global mutable state without init discipline

Validation checklist

• Endpoint contracts match actual responses
• Error paths return stable HTTP semantics
• State/init code is deterministic on restart
• Core functions are typed and reviewable