python-patterns

name	python-patterns
description	Python development principles and decision-making. Framework selection, async patterns, type hints, project structure. Teaches thinking, not copying.
allowed-tools	Read, Write, Edit, Glob, Grep

Python Patterns (2025)

Principles > Memorization.

1. Decision Frameworks

Framework Selection

• API/Microservices: FastAPI (Async, Pydantic).
• Full-Stack/CMS: Django (Batteries-included).
• Simple/Script: Flask (Minimal).
• AI/ML Serving: FastAPI (Performance).

Async vs Sync

• Async (async def): I/O-bound (DB, HTTP), High concurrency.
• Sync (def): CPU-bound, Scripts, Simple apps.
• Golden Rule: Don't block the event loop. Offload CPU work.

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🧠 Aletheia Reasoning Protocol (Pythonic Logic)

Explicit is better than implicit.

1. Generator (Idiom Selection)

• Loop: "List comprehension vs for loop vs map()?".
• Concurrency: "Thread vs Process vs AsyncIO?".
• Data: "Dataclass vs Pydantic vs Dict?".

2. Verifier (Safety Check)

• Blocking: "Did I put a time.sleep() in an async def?".
• Typing: "Did I return Any? (Don't)".
• Memory: "Am I reading the whole file into RAM?".

3. Reviser (Refinement)

• Clean: "Replace if x: return True else: return False with return bool(x)".
• Doc: "Add Google-style docstrings".

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🛡️ Security & Safety Protocol (Python)

1. Serialization: NEVER use pickle on untrusted data. Use json or msgpack.
2. Shell: Avoid shell=True in subprocess.
3. SQL: Use ORM or parametrized queries. No f-strings in SQL.
4. Assert: Don't use assert for business logic (it's optimized out with -O).

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Technical Principles

Type Hints & Pydantic

• Always Type: Params, Returns, Public APIs.
• Pydantic: Use for API schemas, Config (Env vars), Data validation.

Project Structure (FastAPI)

• Layered: routes/ -> services/ -> models/ -> schemas/.
• Feature: users/ (routes, service, schema) -> products/.

Testing

• Tool: pytest + httpx.
• Async: @pytest.mark.asyncio.
• Fixtures: db_session, client, auth_user.

Anti-Patterns

❌ Sync libraries in Async code. ❌ shell=True. ❌ except Exception: pass (Bare except). ❌ Mutable default args (def foo(l=[])).