Picking a Python Version: A Manifesto

Chapter 4. Other Implementations

Several implementations of the Python interpreter exist other than the CPython implementation written and maintained by the Python Software Foundation (that is, actually written by volunteer core contributors, but with the intellectual property maintained by the PSF). The version of Python you can download directly from the python.org website—and the version included in most operating system distributions that have any version—is CPython, so named because it is written in the C programming language (although a lot of bootstrapping is done in Python itself, even for CPython).

PyPy

A fascinating, arcane, and remarkable project is PyPy, an implementation of the Python interpreter written in … Python. Well, OK, technically it is written in a constrained subset of Python called RPython, but every RPython program is a Python program, in any case.

The PyPy website describes the project this way:

PyPy is a fast, compliant alternative implementation of the Python language (2.7.8 and 3.2.5). It has several advantages and distinct features:

• Speed: thanks to its Just-in-Time compiler, Python programs often run faster on PyPy.

• Memory usage: memory-hungry Python programs (several hundreds of MBs or more) might end up taking less space than they do in CPython.

• Compatibility: PyPy is highly compatible with existing python code. It supports cffi and can run popular Python libraries like twisted and django.

• Sandboxing: PyPy provides the ability to run ...