---
name: python-16255e718f65
description: Python engineering guidance for type hints, pydantic validation, httpx usage, pytest conventions, pyproject structure, async patterns, and lightweight dependency injection. Use when building or reviewing Python services and libraries.
---

# Python

Prefer typed, explicit Python with validation at boundaries, modern async I/O, and simple seams over framework-heavy indirection.

## When to Activate

- Add or refactor Python modules
- Choose a model type for request or domain data
- Write an outbound HTTP integration
- Add async handlers or background jobs
- Configure pytest, typing, or packaging
- Replace hidden globals with explicit dependencies
- Review Python code for type and validation drift

## Typing and Modeling

| Pattern | Preferred | Avoid |
| --- | --- | --- |
| Public functions | Full parameter and return annotations | Unannotated signatures |
| Collections | `list[str]`, `dict[str, int]` | `List`, `Dict` unless compatibility requires it |
| Optional values | `str | None` | Implicit `None` returns |

| Need | Use |
| --- | --- |
| External input validation | `pydantic.BaseModel` |
| Internal immutable value object | `@dataclass(frozen=True)` |
| Loosely structured mapping shape | `TypedDict` |

## HTTP and Async

BAD

```python
import requests

response = requests.get(url, timeout=30)
```

GOOD

```python
import httpx

async with httpx.AsyncClient(timeout=10.0) as client:
    response = await client.get(url)
```

| Rule | Why |
| --- | --- |
| Use `async` only for real I/O boundaries | Avoid fake async complexity |
| Do not call blocking I/O inside async handlers | Prevent event loop stalls |
| Batch concurrent I/O with `asyncio.TaskGroup` or `gather` where safe | Improve latency deterministically |

## Project Layout and DI

| Section | Purpose |
| --- | --- |
| `[project]` | Metadata and dependencies |
| `[tool.pytest.ini_options]` | Test discovery and markers |
| `[tool.ruff]` or `[tool.black]` | Lint and format configuration |
| `[tool.mypy]` | Type checking configuration |

| Preferred | Avoid |
| --- | --- |
| Pass collaborators through constructors or function parameters | Global singletons hidden inside modules |
| Build objects in a wiring layer | Import-time side effects creating clients |

BAD

```python
def create_user(data):
    return User(**data)
```

GOOD

```python
class CreateUserInput(BaseModel):
    email: EmailStr
    name: str


def create_user(data: CreateUserInput) -> User:
    return User(email=data.email, name=data.name)
```

## Checklist

- [ ] Public functions and methods have type hints
- [ ] Boundary inputs are validated with pydantic where appropriate
- [ ] `httpx` is used for outbound HTTP unless a project standard overrides it
- [ ] Async code avoids blocking calls
- [ ] `pyproject.toml` centralizes tool configuration
- [ ] Data models use `BaseModel`, `dataclass`, or `TypedDict` intentionally
- [ ] Dependencies are injected explicitly


---
Source attribution: kid-sid
Original project: https://github.com/kid-sid/codex-spellbook/blob/c8c7cac59c0da19cadc52a9b211dd497e1a0b710/skills/python/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 Sidhartha Mohanty 

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: kid-sid
Original project: https://github.com/kid-sid/codex-spellbook/blob/c8c7cac59c0da19cadc52a9b211dd497e1a0b710/skills/python/SKILL.md
Attribution basis: Source repository record

Fields of work: Data & Analytics, Development & Engineering, Product Management
Roles: Backend Developer, Data Scientist, ML / AI Engineer, Product Manager, Technical Product Manager
Specialties: API, Backend, Cross Platform
Tools: Httpx, Pydantic, Pytest
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 37e4124adf4bbb6663ec8f3a4fefe85afb14a82548eb8c45175ddc0c3c5c1d33