- Not to be confused with Cython.
CPython is the default, most-widely used implementation of the Python programming language. It is written in C. In addition to CPython, there are other "production-quality" Python implementations: Jython, written in Java, PyPy and IronPython, which is written for the Common Language Infrastructure. There are also several experimental implementations.
CPython is a bytecode interpreter. It has a foreign function interface with several languages including C, in which one must explicitly write bindings in a language other than Python.
Supported platforms 
Previously supported platforms 
PEP 11 lists platforms which are not supported in CPython by Python Software Foundation. These platforms can still be supported by external ports. See below.
External ports 
These are ports not integrated to Python Software Foundation's official version of CPython, with links to its main development site. Ports often include additional modules for platform-specific functionalities, like graphics and sound API for PSP and SMS and camera API for S60.
Concurrency issues 
A significant drawback to using CPython on a multitasking computer is the presence of a Global Interpreter Lock on each CPython interpreter process, which effectively disables concurrent Python threads within one process. To be truly concurrent in multitasking environment, separate CPython interpreter processes have to be run, which makes establishing communication between them a difficult task, though the multiprocessing module mitigates this somewhat. There is occasional discussion whether to remove the GIL from CPython.