gh-gpshead-cpython-skills-plugins-cpython-skills/skills/cpython-navigation/SKILL.md

name, description

name	description
cpython-navigation	Use this skill when you need to understand the CPython source code structure, find where specific functionality is implemented (C runtime, stdlib, tests, docs), or understand the relationship between different parts of the codebase like modules and their tests.

CPython Source Code Navigation

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

Generates C boilerplate for argument parsing from specially formatted comments in .c files. Output goes to **/clinic/** subdirectories.

NEVER edit files in **/clinic/** subdirectories - they're auto-generated! Edit the source .c file, then run make -C BUILD_DIR clinic.

Scratch Space

NEVER create throwaway files in repo root. Use .claude/sandbox/ for exploration files, test scripts, and prototypes.