Python Pro

What it does

When your agent uses it

• Adding type hints to an untyped Python module and getting mypy strict to pass
• Converting blocking I/O code to async/await
• Building a pytest suite with fixtures, mocking and parametrize
• Packaging a Python project with Poetry and pyproject.toml
• Replacing hand-written __init__ methods with dataclasses

Example prompts

• “Add type annotations to the billing package and make mypy --strict pass.”
• “Rewrite the downloader to use asyncio with a task group instead of threads.”
• “Write pytest tests for the config loader with fixtures and parametrized cases.”
• “Set up pyproject.toml with Poetry, ruff and black for this library.”

Requirements

• Python 3.11 or later
• `mypy`, `black`, `ruff` and `pytest`

Workflow steps

5 steps, taken from the first numbered list in SKILL.md.

1. 1Analyze codebase — Review structure, dependencies, type coverage, test suite
2. 2Design interfaces — Define protocols, dataclasses, type aliases
3. 3Implement — Write Pythonic code with full type hints and error handling
4. 4Test — Create comprehensive pytest suite with >90% coverage
5. 5Validate — Run mypy --strict, black, ruff

What it can do on your machine

Read from SKILL.md and the folder at commit 1be15d8. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Shell commands in SKILL.md call:

  • mypy

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Links to these hosts (documentation or services it may open):

  • github.com
  • synergetic.solutions
  • jeffallan.github.io

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Python Pro loads about 1.6k tokens when it runs, and up to ~13k if it reads all its reference files. Until then it costs about 105 tokens; SKILL.md has 385 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~105

When it runs · the whole SKILL.md, loaded when a task matches

~1.6k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~13k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from Jeffallan/claude-skills at commit 1be15d8, republished under its MIT licence (© Jeffallan). 385 words, ~1,565 tokens.

name

python-pro

description

Use when building Python 3.11+ applications requiring type safety, async programming, or robust error handling. Generates type-annotated Python code, configures mypy in strict mode, writes pytest test suites with fixtures and mocking, and validates code with black and ruff. Invoke for type hints, async/await patterns, dataclasses, dependency injection, logging configuration, and structured error handling.

license

MIT

metadata.author

https://github.com/Jeffallan

metadata.company

https://synergetic.solutions

metadata.version

1.1.0

metadata.domain

language

metadata.triggers

Python development, type hints, async Python, pytest, mypy, dataclasses, Python best practices, Pythonic code

metadata.role

specialist

metadata.scope

implementation

metadata.output-format

code

metadata.related-skills

fastapi-expert, devops-engineer

from pathlib import Path

def read_config(path: Path) -> dict[str, str]:
    """Read configuration from a file.

    Args:
        path: Path to the configuration file.

    Returns:
        Parsed key-value configuration entries.

    Raises:
        FileNotFoundError: If the config file does not exist.
        ValueError: If a line cannot be parsed.
    """
    config: dict[str, str] = {}
    with path.open() as f:
        for line in f:
            key, _, value = line.partition("=")
            if not key.strip():
                raise ValueError(f"Invalid config line: {line!r}")
            config[key.strip()] = value.strip()
    return config

from dataclasses import dataclass, field

@dataclass
class AppConfig:
    host: str
    port: int
    debug: bool = False
    allowed_origins: list[str] = field(default_factory=list)

    def __post_init__(self) -> None:
        if not (1 <= self.port <= 65535):
            raise ValueError(f"Invalid port: {self.port}")

import asyncio
import httpx

async def fetch_all(urls: list[str]) -> list[bytes]:
    """Fetch multiple URLs concurrently."""
    async with httpx.AsyncClient() as client:
        tasks = [client.get(url) for url in urls]
        responses = await asyncio.gather(*tasks)
        return [r.content for r in responses]

import pytest
from pathlib import Path

@pytest.fixture
def config_file(tmp_path: Path) -> Path:
    cfg = tmp_path / "config.txt"
    cfg.write_text("host=localhost\nport=8080\n")
    return cfg

@pytest.mark.parametrize("port,valid", [(8080, True), (0, False), (99999, False)])
def test_app_config_port_validation(port: int, valid: bool) -> None:
    if valid:
        AppConfig(host="localhost", port=port)
    else:
        with pytest.raises(ValueError):
            AppConfig(host="localhost", port=port)

[tool.mypy]
python_version = "3.11"
strict = true
warn_return_any = true
warn_unused_configs = true
disallow_untyped_defs = true

Success: no issues found in 12 source files

© Jeffallan, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 5 other files (references) in skills/python-pro of Jeffallan/claude-skills.

• SKILL.md
• references/async-patterns.md
• references/packaging.md
• references/standard-library.md
• references/testing.md
• references/type-system.md

Open the folder on GitHubat commit 1be15d8