Black is the uncompromising Python code formatter. It is a CLI tool that automatically reformats Python source code to a consistent style, with a focus on determinism and minimal configuration. The repository contains the core formatting engine, a HTTP server (blackd) for on-demand formatting, a GitHub Action for CI integration, and a Vim plugin. The architecture is modular: parsing uses a forked lib2to3 parser (blib2to3) for lenient syntax handling, then a visitor-based line generator produces formatted lines, with specialized transformers for strings, brackets, and comments. It supports Jupyter notebooks, line-range formatting, caching, and parallel execution. The codebase is exceptionally well-tested with hundreds of edge-case test files and a comprehensive test suite. It demonstrates high craftsmanship in areas like tree manipulation, concurrency patterns, and string normalization.
autopep8 is a production-grade Python code formatter that automatically modifies source code to conform to the PEP 8 style guide. It operates as both a CLI tool and a library, using pycodestyle to detect violations and applying targeted fixes for most reported error codes (E1xx, E2xx, E3xx, E4xx, E5xx, E7xx, E9xx, and W6xx). The tool supports incremental formatting, aggressive mode, configuration file inheritance (pyproject.toml, setup.cfg, tox.ini, .pep8, .flake8), and integration with pre-commit hooks and editors like Vim. The entire logic is contained in a single monolithic module (autopep8.py), which includes a complex line-wrapping system for long lines, a reindentation engine, and token-based heuristics. The test suite is exceptionally thorough, with fixture-based regression tests and an 'acid test' framework that validates correctness on arbitrary Python files (including live PyPI packages). While the single-file architecture limits modularity, the internal components are well-factored and demonstrate strong engineering practice.