CPython is the “default” implementation of the
Python programming language, written in C. It was also the first
Python implementation, and was developed by
Guido Van Rossum himself.
The CPython interpreter and the extensive standard library are available in source or binary form without charge for all major platforms, and can be freely distributed.
The CPython implementation is portable: it runs on many brands of Unixes, on Windows, DOS, OS/2, Mac, Amiga and possibly other platforms.
CPython has a good C interface, dynamic loading of C modules, there are interfaces to many system calls and libraries, as well as to various windowing systems (X11, Motif, Tk, Mac, MFC). New built-in modules are easily written in C or C++.
Although CPython is copyrighted, the source code is freely available, and unlike GNU software, it can be commercially re-sold.
Other Python implementations such as Jython (Python for the Java Virtual Machine), Vyper (implemented in Ocaml), Stackless Python (a fork of CPython introducing a paralelism approach of "continuations"), and Managed Python for Microsoft's .NET platform (still very alpha quality) exist, but are less common.