RPython

RPython, short for Restricted Python, is a subset of Python designed for static analysis and translation into lower-level code. It is a core part of the PyPy project and is used to implement PyPy’s interpreter and related components. Programs written in RPython are intended to be translated by the PyPy translation toolchain into C code (and from there into a native executable), enabling a high-performance Python implementation with a Just-In-Time compiler.

RPython emphasizes static typing and a constrained feature set to allow automatic type inference, memory management, and efficient code generation. The subset restricts dynamic language features such as extensive reflection, arbitrary metaprogramming, and some forms of import-time behavior. The standard library within RPython is deliberately minimal, with most system-level functionality provided by PyPy’s own modules. The translation process involves stages that infer types and convert the program into a form suitable for a C backend, producing a standalone runtime with garbage collection and a JIT.

Originating within the PyPy project, RPython is used to implement PyPy’s Python interpreter and its runtime components, as well as other language implementations built on the same toolchain. It is not intended as a general-purpose Python dialect for everyday scripting; rather, it serves as a specialized language for building interpreters, language runtimes, and performance-sensitive software where static translation and memory management are advantageous. While powerful within its niche, RPython offers limited compatibility with CPython and presents restrictions on dynamic features to maintain the translator’s guarantees.