A Language-Based Version Control System for Python

We extend prior work on a language-based approach to versioned software development to support versioned programs with mutable state and evolving method interfaces. Unlike the traditional approach of mainstream version control systems, where a textual diff represents each evolution step, we treat versions as programming elements. Each evolution step, merge operation, and version relationship is represented explicitly in a multifaceted code representation. This provides static guarantees for safe code reuse from previous versions and forward and backwards compatibility between versions, allowing clients to use newly introduced code without needing to refactor their program manually. By lifting versioning to the language level, we pave the way for tools that interact with software repositories to have more insight into a system’s behavior evolution. We instantiate our work in the Python programming language and demonstrate its applicability regarding common evolution and refactoring patterns found in different versions of popular Python packages.