Setting Up Python Projects

Prerequisites

This is a Python-specific extension to myai's setting-up-projects. Load setting-up-projects first for the project shape decision framework, directory layout patterns, bootstrap checklist philosophy, graceful shutdown strategy, and domain adaptation guidance. This skill provides only the Python-specific tooling, config, and code examples.

Also requires engineering-principles (via myai bootstrap).

When to Use This Extension

Use setting-up-projects for all project bootstrap decisions, then load this extension for Python-specific tooling when the project is Python.

For standalone scripts, use writing-scripts (myai). For backend/service repos, start with setting-up-python-backends (Python-specific) after myai's setting-up-backends. For architecture shape decisions on existing projects, use architecting-python-changes.

Templates location

All templates, rules and docs are available at upstream source of this ruleset <https://github.com/quick-brown-foxxx/codingrulespython>.

Python Project Layout

See setting-up-projects for the philosophy behind this layout.

project/
├── src/appname/
│   ├── __init__.py           # __version__ = "0.1.0"
│   ├── __main__.py           # Entry point
│   ├── constants.py          # Shared constants
│   ├── core/                 # Business logic
│   │   ├── models.py         # Data types (dataclasses)
│   │   └── manager.py        # Business operations
│   ├── cli/                  # CLI interface
│   │   ├── commands.py       # Command implementations
│   │   ├── parser.py         # Argument parsing
│   │   └── output.py         # Formatted output helpers
│   ├── ui/                   # Qt GUI (if applicable)
│   │   ├── main_window.py
│   │   ├── dialogs/
│   │   └── widgets/
│   ├── utils/                # Stateless utilities
│   │   ├── paths.py
│   │   └── logging.py
│   ├── wrappers/             # Third-party lib wrappers
│   │   └── some_wrapper.py
│   └── stubs/                # Type stubs for untyped libs
├── tests/
│   ├── unit/
│   ├── integration/
│   ├── fixtures/
│   └── conftest.py
├── scripts/                  # Dev utilities
│   └── check_type_ignore.py
├── docs/
│   └── coding_rules.md       # Copy from rules/coding_rules.md
├── shared/                   # Cross-cutting shared code copied from this repo
│   ├── logging/              # Logging + colored output (if needed)
│   └── shortcuts/            # Keyboard shortcuts (if PySide6 app)
├── shared_tests/             # Generic tests for copied shared modules
│   ├── test_shortcuts_base.py
│   └── test_shortcuts_manager.py
├── AGENTS.md                 # Copy from templates/AGENTS.md, customize
├── CLAUDE.md                 # Symlink → AGENTS.md
├── pyproject.toml            # Copy from templates/pyproject.toml, customize
├── .pre-commit-config.yaml   # Copy from templates/pre-commit-config.yaml
├── .gitignore                # Copy from templates/gitignore
└── .vscode/
    ├── settings.json         # Copy from templates/vscode_settings.json
    └── extensions.json       # Copy from templates/vscode_extensions.json

Python Setup Checklist

See setting-up-projects for the general bootstrap philosophy.

1. Create directory structure:

`` mkdir -p src/APPNAME tests/unit tests/integration tests/fixtures scripts docs .vscode ``

1. Copy baseline files and directories:

- Promote template files into the new project: - templates/pyproject.toml → pyproject.toml (update [project] section) - templates/AGENTS.md → AGENTS.md (fill TODO sections) - templates/pre-commit-config.yaml → .pre-commit-config.yaml - templates/gitignore → .gitignore - templates/vscodesettings.json → .vscode/settings.json - templates/vscodeextensions.json → .vscode/extensions.json - Copy shared/ and sharedtests/ into the new project root if you need the provided building blocks. Trim unused shared modules and dependencies afterward. - Copy rules/codingrules.md → docs/codingrules.md - Create symlink: ln -s AGENTS.md CLAUDE.md - Canonical local bootstrap artifact: skills/setting-up-python-projects/bootstrapdownstreamrepo.sh SOURCEREPO TARGET_REPO

1. Trim copied shared modules (if needed):

- Keep only the shared/ and sharedtests/ subdirectories you actually use - shared/logging/ — colored logging, file rotating logs, CLI output (see setting-up-logging) - shared/shortcuts/ — keyboard shortcuts for PySide6 apps (see setting-up-shortcuts) - Keep matching generic tests in sharedtests/ beside the copied shared modules - Update import paths after copying if the project package name changes

1. Create entry points:

```python # src/APPNAME/init.py version = "0.1.0"

# src/APPNAME/main.py from future import annotations

import sys

def main() -> int: from APPNAME.bootstrap import createservices from APPNAME.cli import buildcli_app

services = createservices(debug=False) app = buildcliapp(services) app(args=sys.argv[1:], progname="APPNAME", standalone_mode=False) return 0

if name == "main": sys.exit(main()) `` Keep main.py thin. Assemble the real presentation layer elsewhere and let main.py do only the final handoff. For multi-interface apps, use the pattern from building-multi-ui-apps`.

1. Create initial test:

```python # tests/test_main.py from future import annotations

import sys

import pytest

from APPNAME.main import main

def testmainruns(monkeypatch: pytest.MonkeyPatch) -> None: monkeypatch.setattr(sys, "argv", ["APPNAME"]) assert main() == 0 ```

1. Initialize environment:

``bash git init uv sync --all-extras --group dev uv run poe lintfull uv run poe test ` After setup, keep using project-local commands through uv: uv run python, uv run pytest, uv run ruff, uv run basedpyright, uv run poe, uv run pre-commit. The default verification flow is uv run poe lintfull followed by uv run poe test`.

1. Verify everything works:

- uv run poe lint_full passes (basedpyright + Ruff check/format + custom linters) - uv run poe test passes

Python Graceful Shutdown

See setting-up-projects for the shutdown strategy decision framework.

Scripts and simple CLIs

# __main__.py
def main() -> int:
    try:
        return run()
    except KeyboardInterrupt:
        return 130  # 128 + SIGINT(2), Unix convention

Subprocess wrappers

Always pass startnewsession=True — creates a process group so you can kill the entire tree, not just the parent.

Quick subtask (immediate kill):

import os, signal, subprocess

process = subprocess.Popen(cmd, start_new_session=True)
try:
    process.wait()
except KeyboardInterrupt:
    os.killpg(process.pid, signal.SIGKILL)

Complex tool wrapper (escalation):

process = subprocess.Popen(cmd, start_new_session=True)
try:
    process.wait()
except KeyboardInterrupt:
    os.killpg(process.pid, signal.SIGTERM)
    try:
        process.wait(timeout=5.0)
    except subprocess.TimeoutExpired:
        os.killpg(process.pid, signal.SIGKILL)

Async subprocess (complex apps using asyncio):

process = await asyncio.create_subprocess_exec(*cmd, start_new_session=True)
try:
    await process.wait()
except asyncio.CancelledError:
    process.terminate()
    try:
        await asyncio.wait_for(process.wait(), timeout=5.0)
    except TimeoutError:
        process.kill()
    raise

Bootstrap Script

Use skills/setting-up-python-projects/bootstrapdownstreamrepo.sh as the canonical local bootstrap artifact. It promotes template files into place, copies shared/, sharedtests/, and docs files, creates CLAUDE.md, then runs uv sync --all-extras --group dev, uv run poe lintfull, and uv run poe test in the downstream repo.

Python-Specific Customization

See setting-up-projects for the general domain adaptation framework.

Wrapper enforcement with banned-api

When the project wraps third-party libraries (for typing, platform abstraction, or swappability), enforce wrapper usage via ruff's flake8-tidy-imports.banned-api in pyproject.toml:

[tool.ruff.lint.flake8-tidy-imports.banned-api]
"soundcard".msg = "Use src/wrappers/audio_backend.py instead"
"faster_whisper".msg = "Use src/wrappers/transcriber.py instead"

Wrap when a library is poorly typed (need typed facade), platform-specific (need abstraction layer), or swappable (need stable internal API). The template pyproject.toml has commented examples — uncomment and customize per project.

Inside the wrapper files themselves, suppress the ban with a per-file ruff ignore: "src/wrappers/*".msg = "" in the banned-api config, or use # noqa: TID251 on individual import lines.

Research before building

When setting up a project in an unfamiliar domain or with unfamiliar libraries:

1. Research the domain's conventions — look up how well-maintained projects in the same space are structured
2. Check library compatibility — verify libraries work together and with basedpyright strict mode (some libraries have poor type stubs; plan wrappers early)
3. Identify domain-specific tooling — some domains have their own linters, formatters, or validation tools
4. Check for basedpyright known issues — some libraries (numpy, pandas, SQLAlchemy) need specific configuration or stub packages to work cleanly in strict mode

Quick customization checklist

• Directory layout matches the domain, not the generic template
• Dependencies are domain-appropriate (researched, not guessed)
• AGENTS.md describes this project, not a generic Python project
• coding_rules.md has domain-specific additions if needed
• Test structure reflects what matters most for this project
• basedpyright config accounts for domain-specific library quirks

Handoff

• Use setting-up-python-backends for backend repos (after setting-up-backends)
• Use building-multi-ui-apps for GUI+CLI sharing a core
• Use writing-python-code for implementation rules

Related Skills

• setting-up-projects (myai) — Parent skill. Load first for project shape decisions and bootstrap philosophy.
• engineering-principles (myai) — Foundation. Language-agnostic philosophy.
• architecting-changes (myai) — Architecture decisions.
• writing-scripts (myai) — For single-file scripts (Python and TypeScript/Node examples).
• setting-up-python-backends — For backend/service repos.
• testing-python — Python testing setup.
• writing-python-code — Python coding rules.