What is PyPy? — PyPy is a replacement for CPython. It is built using the RPython language that was co-developed with it. RPython is a subset of Python and can be translated to C. The main reason to use it instead of CPython is speed: it runs generally faster due to JIT compilation. PyPy implements Python 2.7.10. It supports all of the core language, passing the Python test suite (with minor modifications that were already accepted in the main python in newer versions). It supports most of the commonly used Python standard library modules.