python-coding

A set of rules for writing, reviewing, and testing Python 3.14 code in the appkit project.

In plain words
What is it for?
Use it when creating or changing Python modules, reviewing Python code, or adding tests.
Why use it?
It keeps code style, logging, type annotations, file size, testing, and project commands consistent. This reduces avoidable review issues and maintenance work.

Skill for Claude CodeCodex

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.

agentmods
npx agentmods add skills/jenreh/appkit/python-coding
Any agent
npx skills add jenreh/appkit --skill python-coding
Clone the repo
git clone --depth 1 https://github.com/jenreh/appkit

Made for: Claude Code, Codex.

Per session 57 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,086 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin 95% copy Near-identical to another mod 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.

ModelPer sessionOnce invoked
Fable 5 $0.00057 $0.01086
Opus 5 $0.00028 $0.00543
Sonnet 5 $0.00011 $0.00217
Haiku 4.5 $0.00006 $0.00109

Measured yesterday against content hash d4dcc40f6e48, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

python-coding 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 yesterday.

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.

Origin

This is a copy

95% identical to writing-python-code — 9 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

.claude/skills/python-coding/SKILL.md · 125 lines

How it starts

The opening of the file, as written. The whole thing — 125 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Writing Python Code

Quick reference

  • Python 3.14 only; deps via uv; line length 88 chars (Ruff/Black).
  • No f-strings in logger calls — use log.info("x: %s", val).
  • Type annotations on every function and method.
  • Files ≤ 1000 lines — refactor via Extract Class, Mixins, Strategy, etc.
  • Coverage ≥ 80% for non-Reflex classes and Reflex State classes.
  • Task runner: task format, task lint, task test (not make).

Code style

Logging

import logging

log = logging.getLogger(__name__)

log.info("Loaded items: %d", count)          # ✅ parameterized
# log.info(f"Loaded items: {count}")         # ❌ f-string

Never use print or printf. Log levels: debug → internal state (default), info → milestones, warning → recoverable, error → serious.

Type hints

def process(data: dict[str, Any], count: int = 0) -> list[str]: ...

async def handler(value: str) -> AsyncGenerator[Any, Any]:
    yield
  • Do not mix Literal[...] with str — pick one.
  • Remove unused imports immediately (F401).
  • Remove unused args or prefix with _ (ARG001).

Imports & formatting

  • Ruff handles lint + format; run task format before committing.
  • Break long calls/strings to fit 88 chars.

Ruff rules to watch (project-specific)

Code Rule Fix
UP031 No %-formatting outside logger calls — use f-strings Replace "x %s" % val with f"x {val}"
I001 Import order Auto-fixed by task format
PLC0415 No local imports inside functions or test methods Move to top of file
B017 pytest.raises(Exception) too broad Use specific exception, e.g. pytest.raises(ValidationError)

File size rule

No Python file may exceed 1000 lines. When approaching the limit, apply clean code refactoring strategies.

Design patterns & refactoring strategies: See skill python-clean-code.

Testing

Coverage target: ≥ 80% for services, repositories, models, utilities, and Reflex State classes. UI component rendering is best-effort.

Read the full file on GitHub · 125 lines

Files

What ships with it

1 file 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.

  1. yesterday First seen · 125 lines · 57 tokens per session scan A d4dcc40f6e48

Subscribe to this mod's changes

python-coding is a skill published in the GitHub repository jenreh/appkit (4 stars, last pushed 6d ago), licensed MIT. It adds 57 tokens to every session and 1,086 once invoked, about $0.0003 per session on Opus 5. A static security scan graded it A with 0 findings. It is 95% identical to writing-python-code, differing in 9 lines, and is treated as a copy.

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