python

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Develop Python applications using modern patterns, uv, functional-first design, and production-first practices. Use this whenever working with .py files, pyproject.toml, uv commands, pip/pip3, poetry, virtualenv/venv, inline script metadata, or Python tooling like pytest, mypy, ruff, asyncio, itertools, functools, or dataclasses. If the task involves running Python, managing Python dependencies, creating environments, or building Python packages, load this skill and prefer uv-oriented workflows.

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Sourceanntnzrb/agents

Added on2026-03-07

NPX Install

npx skill4agent add anntnzrb/agents python

SKILL.md Content

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Python Development

Functional-first, production-first Python 3.14+ with uv, type safety, immutability, and small composable modules.

Activation Triggers

```
.py
```
files,
```
pyproject.toml
```
, uv commands, Python packaging
pip, pip3, poetry, venv, virtualenv, inline script metadata
Python, typing, asyncio, pytest, mypy, ruff, dataclasses, itertools, functools
Async I/O, data pipelines, CLI tooling, validation, parsing, test strategy

Workflow

text

1. MODEL    -> types, invariants, boundaries
2. COMPOSE  -> pure functions, pipelines, small modules
3. VALIDATE -> parse at edges, return errors early
4. TEST     -> pytest, fixtures, async tests
5. HARDEN   -> ruff + format + mypy + regression tests

Core Principles

Functional core, imperative shell
Immutability by default; copy-on-write
Explicit types and error paths
Small composable units
Production defaults: logging, config, timeouts, retries
Prefer
```
uv
```
for running Python, dependency management, environments, scripts, and builds

When to Use

New or refactored Python modules
Async I/O, data pipelines, CLI tooling
Type-heavy APIs, validation, parsing
Test strategy or flaky tests
Any request that mentions Python setup, Python dependencies, virtual environments, or script execution

When Not to Use

Non-Python runtimes
Browser E2E tests (use Playwright)

uv-first workflow

Use

uv

instead of raw

python

,

pip

,

poetry

, or

python -m venv

.

Quick reference

bash

uv run python script.py
uv run pytest
uv run --with requests python script.py
uv add requests pydantic httpx
uv add --dev pytest pytest-asyncio mypy ruff
uv venv
uv run python -m ast path/to/file.py >/dev/null
uv init --script example.py --python 3.12
uv add --script example.py requests rich
uv lock --script example.py

Prefer these replacements

```
python script.py
```
->
```
uv run python script.py
```
```
python -m pytest
```
->
```
uv run pytest
```
```
pip install x
```
->
```
uv add x
```
```
python -m venv .venv
```
->
```
uv venv
```

python -m py_compile foo.py

->

uv run python -m ast foo.py >/dev/null

Inline script metadata

For standalone scripts, prefer uv inline metadata over ad-hoc setup.

python

# /// script
# requires-python = ">=3.12"
# dependencies = [
#   "requests<3",
#   "rich",
# ]
# ///

Then run:

bash

uv run script.py

Helpful commands:

bash

uv init --script script.py --python 3.12
uv add --script script.py requests rich
uv lock --script script.py

For executable scripts:

python

#!/usr/bin/env -S uv run --script
# /// script
# dependencies = ["httpx"]
# ///

Project quick start

bash

uv init my-project && cd my-project
uv add requests pydantic httpx
uv add --dev pytest pytest-asyncio mypy ruff

uv run python script.py
uv run pytest

Quality gates

bash

uv run ruff check src/
uv run ruff format --check src/
uv run mypy src/
uv run pytest

Build backend

Use

uv_build

for pure Python packages. For extension modules, prefer another backend such as

hatchling

.

toml

[build-system]
requires = ["uv_build>=0.9.28,<0.10.0"]
build-backend = "uv_build"

Prefer the standard

src/

layout unless the repo has a strong reason not to.

Must / Must Not

MUST: type hints on public APIs; validate inputs at boundaries; prefer pathlib
MUST: use
```
uv
```
for running Python, adding deps, script metadata, and env setup
MUST NOT: use raw
```
pip
```
,
```
pip3
```
,
```
poetry
```
, or
```
python -m venv
```
when uv is the intended workflow
MUST NOT: use mutable default args; bare except; mix sync/async in one call chain

Notes

Core patterns, async examples, and anti-patterns live in

reference.md

and the cookbooks. Read the relevant cookbook when the task narrows:

async work ->
```
cookbook/async.md
```
functional structure ->
```
cookbook/patterns*.md
```
tests ->
```
cookbook/testing*.md
```
language features ->
```
cookbook/modern*.md
```

Research tools

bash

# gh search code for real-world examples
gh search code "asyncio.TaskGroup(" --language=python
gh search code "class.*Protocol):" --language=python
gh search code "async with httpx.AsyncClient(" --language=python

References

reference.md - Data structures, best practices, idioms, error handling
patterns.md - Functional patterns
async.md - Async/await deep dive
testing.md - pytest patterns & fixtures
design-patterns.md - Builder, DI, Factory, Strategy, Repository
modern.md - Python 3.8-3.14 key features

python

NPX Install

Tags

SKILL.md Content

Python Development

Activation Triggers

Workflow

Core Principles

When to Use

When Not to Use

uv-first workflow

Quick reference

Prefer these replacements

Inline script metadata

Project quick start

Quality gates

Build backend

Must / Must Not

Notes

Research tools

References