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jmlrtjmlrt/skills/python-development/SKILL.md

python-development

Skill0 starsChanged 4 months agoMITView on GitHub

Guide Python development with greenfield defaults and brownfield flexibility. Apply when writing, maintaining, or reviewing Python code to ensure consistency with modern tooling (uv, ruff, ty, pytest, pre-commit) and patterns (CLI separation, type safety, error handling).

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The file

We split this skill into the rules it gives an agent

4 rules. 0 are common, 3 are distinctive, and 1 is very specific to this project.

  • 0

    Common

    Most of the 10 edited versions we read keep these.

  • 3

    Distinctive

    This author's own choices. Worth a look.

  • 1

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Distinctive:

    Read the existing code and tooling first and match it.

    line 41
  2. Distinctive:

    Keep the existing build system.

    line 44
  3. Very specific:

    Keep a flat tests/ under ~50 tests.

    line 47
  4. Distinctive:

    When a blocker is found, grep for the same pattern across the codebase and report every instance.

    line 65

“Common” is measured: kept by at least 6 in 10 of the 10 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Python Development

Personal tooling defaults and non-obvious patterns. Generic Python knowledge is assumed.

Supporting Files

  • tooling.md — read when setting up a greenfield project: pyproject.toml, Makefile, .pre-commit-config.yaml templates (use them verbatim)
  • patterns.md — read when structuring a CLI, defining exceptions, or writing tests that touch module-level state

Toolchain

uv (uv sync, uv run), ruff (check + format), ty (or mypy if the repo uses it), pytest, pre-commit; make targets install, test, lint, fmt/format, typecheck, check. Older repos may use other tools (e.g. poetry): read the Makefile first.

Greenfield Defaults

  • Python 3.12 (.python-version), hatchling, src/ layout with cli.py, commands/, core/; tests/conftest.py.
  • Modern type hints on every function (str | None, list[str], collections.abc), no from __future__.
  • One-line docstring per function and module; no Args:/Returns: sections.
  • Absolute imports only; pathlib.Path only; @dataclass for models with 2+ fields.
  • Output via typer.echo; add Rich + logging only when a --verbose flag is requested.
  • Config: tomllib + TOML file; Pydantic only for nested config needing validation. Env vars only for secrets or CI overrides.
  • __init__.py empty, or just __version__ when the CLI has --version.
  • TYPE_CHECKING guard only after hitting a real circular import.
  • Done when make install && make check passes and pre-commit install is enabled.

Brownfield

Read the existing code and tooling first and match it; don't retrofit greenfield defaults or change tooling unless asked.

  • Keep the existing build system; missing → hatchling.
  • Python ≤3.11 → keep it.
  • Type checking: 80%+ hint coverage → ty check; less → ruff check only; none → tests only.
  • Keep a flat tests/ under ~50 tests.
  • Refactor argparse/custom CLIs to Typer only when actively developing them.

Review Checklist

Blockers

  • Bare except: or except Exception without re-raising
  • Unused imports or dead code
  • Hardcoded secrets

Nits

  • Missing type hints or docstrings; os.path; mutable default arguments
  • Re-raise without from e; raising base Exception instead of a domain error
  • Tests touching real filesystem or env without tmp_path / monkeypatch
  • Module-level mutable state not isolated by an autouse fixture — see patterns.md

When a blocker is found, grep for the same pattern across the codebase and report every instance.

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