Python3 Development

Opinionated Python Development Skill

Python development guide for modern Python 3.11-3.14 patterns.

Domain-Specific Skill Routing

Testing

Load /python3-development:comprehensive-test-review when reviewing test quality or performing test audits (full checklist).

Load /python3-development:analyze-test-failures when analyzing failing tests or debugging test failures (balanced investigation).

Load /python3-development:test-failure-mindset when resetting approach to test failures (tests-as-spec mindset).

CLI and UI libraries

Load /python3-development:typer-and-rich when building CLIs with Typer and Rich together (integration, width handling, examples).

Load /python3-development:typer when working on Typer-only CLI patterns (commands, arguments, Typer features).

Load /python3-development:rich when working on Rich output (tables, panels, progress, trees).

Load /python3-development:textual when building terminal UIs with Textual.

Development workflows

Load /python3-development:create-feature-task when creating a structured feature task with tracking and phases.

Load /python3-development:use-command-template when creating a new Claude Code skill from the template workflow.

Code quality

Load /python3-development:modernpython when applying modern Python 3.11+ patterns or modernizing legacy code (PEP-grounded).

Load /python3-development:shebangpython when validating shebangs or PEP 723 inline script metadata.

Load /python3-development:stinkysnake when running progressive quality improvement (static analysis, typing, modernization plan, TDD loop).

Extended tool matrix

Load /python3-development:specialist-skill-routing when the task involves uv, Hatchling, ty, pre-commit, packaging, or other specialists not listed above (full trigger map inside that skill).

Skill Architecture

Bundled Resources (Included in This Skill)

Reference Documentation:

• references/python3-standards.md — Unified Python 3.11+ standards, knowledge graph, process graph, and how to amend them (consult when enforcing plugin-wide rules)
• references/user-project-conventions.md — Conventions from production projects; consult when starting or matching an existing project style
• references/modern-modules.md - 50+ library guides with usage patterns and best practices
• references/tool-library-registry.md - Development tools catalog for linting, testing, and build automation
• references/python-development-orchestration.md - Detailed workflow patterns for TDD, feature addition, refactoring, and code review

Specialist Skills (routing commands — see Domain-Specific Skill Routing):

• Testing: comprehensive-test-review, analyze-test-failures, test-failure-mindset
• CLI/UI: typer-and-rich, typer, rich, textual
• Workflows: create-feature-task, use-command-template
• Quality: modernpython, shebangpython, stinkysnake
• More: specialist-skill-routing (uv, Hatchling, ty, packaging, …)

Scripts and Assets:

• Example scripts demonstrating patterns
• Configuration templates and boilerplate

System Tools (install via package manager or uv):

• uv - Python package and project manager (required)
• ruff - Linter and formatter
• ty - Primary static type checker (Astral); default for new work — see /astral:ty
• mypy - Static type checker; use when the project already configures it — do not force migration away from mypy
• pyright / basedpyright - Use when the project already standardizes on them
• pytest - Testing framework
• pre-commit - Git hook framework
• mutmut - Mutation testing (for critical code)
• bandit - Security scanner (for critical code)

Installation Notes:

• Use the uv skill for comprehensive uv documentation and package management guidance

Core Concepts

Python Development Standards

This skill provides modern Python 3.11+ standards, quality gates, and reference documentation for Python development.

Consult references/python3-standards.md when applying shared rules for:

• Architecture Standards (Layered architecture, Separation of concerns)
• Python Standards (Native type hints, Google-style docstrings, Fail-fast error handling)
• CLI Standards (Typer/Rich)
• Service Integration Standards (Protocol classes)
• Testing Standards (pytest-mock, 80% coverage)
• Identifier Naming Standards (expand acronyms in public names; see §1.5)

Python Development Process Graph

For the canonical development lifecycle, see references/python3-standards.md (Section 3).

Docstring standard Google style (Args/Returns/Raises sections). See references/user-project-conventions.md for ruff pydocstyle configuration (convention = "google").

Pyproject.toml template variables

All pyproject.toml examples use explicit template variables (e.g., {{project_name_from_directory_or_git_remote}}) instead of generic placeholders. Replace every template variable with actual values before writing files. See references/tool-library-registry.md#18-pyprojecttoml-template-variable-reference for variable reference, sourcing methods, and verification steps.

Command Usage

/python3-development:modernpython

Purpose: Comprehensive reference guide for Python 3.11+ patterns with official PEP citations

When to use:

• As reference guide when writing new code
• Learning modern Python 3.11-3.14 features and patterns
• Understanding official PEPs (585, 604, 695, etc.)
• Identifying legacy patterns to avoid
• Finding modern alternatives for old code

Note: This is a reference document to READ, not an automated validation tool. Use it to guide your implementation choices.

Usage:

/python3-development:modernpython
→ Loads comprehensive reference guide
→ Provides Python 3.11+ pattern examples
→ Includes PEP citations with research tool guidance (prefer MCP tools: Ref/exa over WebFetch)
→ Shows legacy patterns to avoid
→ Shows modern alternatives to use
→ Framework-specific guides (Typer, Rich, pytest)

Research tool preference for PEP documentation:
1. mcp__Ref__ref_search_documentation(query="PEP {number} Python enhancement proposal")
2. mcp__exa__get_code_context_exa(query="PEP {number} implementation examples")
3. WebFetch as fallback

> [Web resource access, definitive guide for getting accurate data for high quality results](./references/accessing_online_resources.md)

With file path argument:

/python3-development:modernpython src/mymodule.py
→ Loads guide for reference while working on specified file
→ Use guide to manually identify and refactor legacy patterns

/python3-development:shebangpython

Purpose: Validate correct shebang for ALL Python scripts based on their dependencies and execution context

When to use:

• Creating any standalone executable Python script
• Validating script shebang correctness
• Ensuring scripts have proper execution configuration

Required for: ALL executable Python scripts (validates shebang matches script type)

What it validates:

• Stdlib-only scripts: #!/usr/bin/env python3 (no PEP 723 needed - nothing to declare)
• Scripts with dependencies: #!/usr/bin/env -S uv --quiet run --active --script + PEP 723 metadata declaring those dependencies
• Package executables: #!/usr/bin/env python3 (dependencies via package manager)
• Library modules: No shebang (not directly executable)

See: references/PEP723.md for details on inline script metadata

Pattern:

/python3-development:shebangpython scripts/deploy.py
→ Analyzes imports to determine dependency type
→ **Corrects shebang** to match script type (edits file if wrong)
→ **Adds PEP 723 metadata** if external dependencies detected (edits file)
→ **Removes PEP 723 metadata** if stdlib-only (edits file)
→ Sets execute bit if needed
→ Provides detailed verification report

Quality Gates

For the mandatory quality gate sequence (linting, type checking, tests, full-file review, shebang validation), activate the /python3-development:python-cli-architect skill.

Diagnostic Rules

error[unresolved-import]: Cannot resolve imported module 'X' — Add the directory containing module X to [tool.ty.environment] extra-paths in pyproject.toml; run uv run ty check <path> to verify; if errors persist, confirm pyproject.toml is the config ty is reading (a ty.toml in the project root takes precedence and pyproject.toml will be ignored).

Standard Project Structure

For project directory layout, Hatchling configuration, and package naming rules, activate the /python3-development:python-cli-architect skill.

Integration

Reference Example (Bundled)

Complete working example (bundled): Load Skill(skill="python3-development:typer-and-rich") to access python-cli-demo.py — a complete CLI demo demonstrating all recommended patterns.

This reference implementation demonstrates all recommended patterns:

• PEP 723 metadata with correct shebang
• Typer + Rich integration
• Modern Python 3.11+ (StrEnum, Protocol, TypeVar, Generics)
• Annotated syntax for CLI params
• Async processing
• Comprehensive docstrings

This file is bundled with this plugin to keep the workflow self-contained. Use it as reference when creating CLI tools.

Using Asset Templates

When creating new Python projects, copy standard configuration files from the skill's assets directory to ensure consistency with established conventions:

Reason: Templates implement proven patterns and save setup time.

Asset Directory Location (in plugin): ./assets/

Available Templates:

1. version.py - Dual-mode version management (hatch-vcs + importlib.metadata fallback)

   cp "${CLAUDE_PLUGIN_ROOT}/skills/python3-development/assets/version.py" "packages/{package_name}/version.py"
   

2. hatch_build.py - Build hook for binary/asset handling (only if needed)

   mkdir -p scripts/
   cp "${CLAUDE_PLUGIN_ROOT}/skills/python3-development/assets/hatch_build.py" "scripts/hatch_build.py"
   

3. .markdownlint.json - Markdown linting configuration

   cp "${CLAUDE_PLUGIN_ROOT}/skills/python3-development/assets/.markdownlint.json" "."
   

4. .pre-commit-config.yaml - Standard git hooks configuration

   cp "${CLAUDE_PLUGIN_ROOT}/skills/python3-development/assets/example.pre-commit-config.yaml" ".pre-commit-config.yaml"
   
   # Install hooks using pre-commit or prek (whichever is available)
   # Both tools use the same configuration file and have identical interfaces
   uv run pre-commit install  # or: uv run prek install
   

5. .editorconfig - Editor formatting settings

   cp "${CLAUDE_PLUGIN_ROOT}/skills/python3-development/assets/.editorconfig" "."
   

These templates implement the patterns documented in references/user-project-conventions.md and ensure all projects follow the same standards for version management, linting, formatting, and build configuration.

Detailed Documentation

Reference Documentation

PEP 723 Specification: references/PEP723.md - User-friendly guide to PEP 723 inline script metadata with examples and migration patterns

Exception Handling and Typer/Rich Examples: Load Skill(skill="python3-development:typer-and-rich") — covers exception chain prevention, Typer exit patterns, Rich non-TTY display solutions, and working executable examples including typer_examples/ scripts and python-cli-demo.py.

Module Reference: references/modern-modules.md - Comprehensive guide to 50+ modern Python libraries with deep-dive documentation for each module including usage patterns and best practices

Tool Registry: references/tool-library-registry.md - Catalog of development tools, their purposes, and usage patterns for linting, testing, and build automation

Navigating Large References

To find specific modules in modern-modules.md:

grep -i "^### " references/modern-modules.md

To search for tools by category in tool-library-registry.md:

grep -A 5 "^## " references/tool-library-registry.md

To locate workflow patterns in python-development-orchestration.md:

grep -i "^## " references/python-development-orchestration.md

External Commands

These skills are bundled with this plugin and available as slash commands:

• ../modernpython/SKILL.md - Python 3.11+ patterns and PEP references
• ../shebangpython/SKILL.md - PEP 723 validation and shebang standards

Summary

• Modern Python 3.11+ standards and patterns
• Quality gates: ruff, ty (default type check), mypy/pyright when project uses them, pytest (>80% coverage)
• Command standards: /python3-development:modernpython, /python3-development:shebangpython
• Reference documentation for 50+ modern Python modules
• Tool and library registry