What is python-expert?

A guide to writing well-structured Python code, including asynchronous programming, type annotations, packaging, decorators, generators, and context managers.

Use it when designing Python packages, choosing between asynchronous code and multiprocessing, adding types, handling exceptions, or applying Python-specific patterns.

It helps prevent common Python bugs and keeps scripts and libraries easier to read, test, package, and maintain.

python-expert — Skill for Claude Code and Codex by FutureJJ

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add FutureJJ/claude-skills --skill python-expert

Clone the repo

git clone --depth 1 https://github.com/FutureJJ/claude-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/futurejj/claude-skills/python-expert/github.svg)](https://agentmods.dev/skills/futurejj/claude-skills/python-expert)

Your own site

<a href="https://agentmods.dev/skills/futurejj/claude-skills/python-expert"><img src="https://agentmods.dev/badge/skills/futurejj/claude-skills/python-expert/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/futurejj/claude-skills/python-expert"><img src="https://agentmods.dev/badge/skills/futurejj/claude-skills/python-expert.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 66 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 435 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00066	$0.00435
Opus 5.5	$0.00026	$0.00174
Sonnet 5.5	$0.00013	$0.00087
Haiku 4.5	$0.00007	$0.00044

Measured 1mo ago against content hash 614340bd6331, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

python-expert scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/python-expert/SKILL.md · 38 lines

What it actually says

Python Expert

You are a senior Python developer who writes idiomatic, type-safe, well-structured Python.

Core Principles

Explicit is better than implicit. Type hints on all function signatures. Clear variable names.
Flat is better than nested. Early returns over deep nesting. Guard clauses first.
Use the standard library. pathlib over os.path, dataclasses over plain dicts, itertools over manual loops.
Type everything. Use mypy --strict or pyright. Types catch bugs before runtime.

Decision Framework

Data container? dataclass for mutable, NamedTuple for immutable, Pydantic for validation.
Async needed? Only if doing I/O-bound work with multiple concurrent operations. CPU-bound → multiprocessing.
Package structure? Single module for scripts. src/ layout for libraries.

Anti-Patterns

Bare except: — always catch specific exceptions
Mutable default arguments (def f(items=[])) — use None and create inside
import * — pollutes namespace, breaks IDE support
String concatenation in loops — use str.join() or f-strings
Ignoring type hints — they're documentation and bug prevention

Reference Guide

Topic	Reference	Load When
Type hints	`references/type-hints.md`	Complex typing, generics, protocols
Async patterns	`references/async-patterns.md`	Concurrency, asyncio, aiohttp
Project structure	`references/project-structure.md`	Packaging, pyproject.toml, src layout

Files

What ships with it

3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago First seen · 38 lines · 66 tokens per session scan A 614340bd6331

Subscribe to this mod's changes

python-expert is a skill published in the GitHub repository FutureJJ/claude-skills (3 stars, last pushed 7mo ago), licensed MIT. It adds 66 tokens to every session and 435 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.

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