CPythonstyle

CPythonstyle is an informal coding style guideline used by the CPython project to maintain a cohesive and readable codebase across its C core, extensions, and Python modules. It serves as a practical standard for contributors rather than a formal external specification.

It is not a separate PEP but a living set of conventions documented in the project’s contributor guidelines. The guideline aims to improve readability, reduce review time, and simplify onboarding for new contributors, while allowing for occasional deviations that are discussed and recorded as exceptions.

Core principles cover naming conventions, indentation, comments, and documentation. In C sources, CPythonstyle emphasizes consistent whitespace, clear function and type names, and careful use of the Python C API, including reference counting and error handling. Python code follows parallel goals where applicable, prioritizing clarity and maintainability in module code and tests.

Tools and enforcement: internal linting, static analysis, and continuous integration checks help codify and uphold CPythonstyle. Pre-commit hooks and structured code reviews support uniformity, and any deviations are typically resolved through discussion and update of the guidelines.

Relation to broader Python standards: CPythonstyle aligns with PEP 7 for Python’s C API style and PEP 8 for Python code, but it remains an internal standard tailored to the CPython project’s historical conventions and practical needs. It complements project-wide quality controls rather than replacing them.

History and governance: CPythonstyle evolves through core developer discussions and pull request reviews. It reflects CPython’s emphasis on reliability, maintainability, and a smooth onboarding experience for new contributors, while adapting to the evolving needs of the codebase.