# Dev > Use this skill when working in the CPython repository for any development task - fixing bugs, adding features, understanding code, or making contributions. Provides codebase orientation and coordinates loading of specialized skills (build, style, docs, jit) as your workflow progresses. - Skill: `tomevault-io/dev-4` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/dev-4` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/dev-4/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Productivity - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/dev-4 --- # CPython Development You are working in the CPython repository - the implementation of the Python language runtime and standard library itself. ## Load Specialized Skills As Needed This skill provides orientation. **Load additional skills when your task requires them:** - **Load `build` skill when**: compiling CPython, running tests, verifying changes work, debugging test failures, or checking if your fix is correct - **Load `style` skill when**: preparing commits, running pre-commit hooks, checking code style, or validating changes before pushing - **Load `docs` skill when**: editing files in `Doc/`, adding version markers, creating NEWS entries, or updating documentation - **Load `jit` skill when**: working on the JIT compiler, modifying `Tools/jit/` or `Python/jit.c`, debugging JIT-specific failures, or changing bytecodes that affect stencil generation ## Recommended Tools Prefer these tools when available: `rg`, `gh`, `jq` ## Source Code Structure **`Lib/`** - Python standard library (pure Python). Example: `Lib/zipfile.py` **`Modules/`** - C extension modules for performance/low-level access. Example: `Modules/_csv.c` **`Objects/` and `Python/`** - Core types (list, dict, int), builtins, runtime, interpreter loop **`Include/`** - C header files for public and internal C APIs **`Lib/test/`** - All unittests - Test naming: `test_{module_name}.py` or `test_{module_name}/` - Examples: `Lib/zipfile.py` → `Lib/test/test_zipfile**`, `Modules/_csv.c` → `Lib/test/test_csv.py` - Test packages require `load_tests()` in `test_package/__init__.py` to work with `python -m test` **`Doc/`** - Documentation in .rst format (source for python.org docs), builds to `Doc/build/` **`InternalDocs/`** - Maintainer documentation (`InternalDocs/README.md` is the starting point) **`Tools/`** - Build tools like Argument Clinic, development utilities ## Argument Clinic **`**/clinic/**` subdirectories are auto-generated** - never edit these directly. Load the `build` skill for regeneration commands. ## Engineering Notebooks ALWAYS load and maintain notebooks when working on features or PRs: - **For PRs**: `.claude/pr-{PR_NUMBER}.md` - **For branches**: `.claude/branch-{branch_name_without_slashes}.md` (when not on `main`) Keep notebooks updated with learnings and project state as you work and after commits. Include: problem statement, key findings, file locations, design decisions, testing strategy, and status. ## Scratch Space **NEVER create throwaway files in repo root.** Use `.claude/sandbox/` for exploration files, test scripts, and prototypes. ## Optional Developer Resources - **Developer Guide**: If `REPO_ROOT/../devguide/` exists, see `developer-workflow/` and `documentation/` subdirectories - **PEPs**: May exist in `REPO_ROOT/../peps/` tree - reference relevant PEPs when working on changes ## Typical Workflow 1. **Understand the task** - explore code, read relevant files 2. **Make changes** - edit source files 3. **Build and test** - load `build` skill, compile, run tests 4. **Validate style** - load `style` skill, run pre-commit and patchcheck 5. **Update docs** - if needed, load `docs` skill for documentation changes --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/gpshead) — claim your Tome and manage your conversions.