Though there is one Python implementation which is by far the most popular, there are some alternate implementations which are of particular interest to different audiences.
Known implementations include:
This is the original and most-maintained implementation of Python, written in C. New language features generally appear here first.
Python implemented in Java. This implementation can be used as a scripting language for Java applications, or can be used to create applications using the Java class libraries. It is also often used to create tests for Java libraries. More information can be found at the Jython website.
Python for .NET
This implementation actually uses the CPython implementation, but is a managed .NET application and makes .NET libraries available. This was created by Brian Lloyd. For more information, see the Python for .NET home page.
An alternate Python for .NET. Unlike Python.NET, this is a complete Python implementation that generates IL, and compiles Python code directly to .NET assemblies. It was created by Jim Hugunin, the original creator of Jython. For more information, see the IronPython website.
An implementation of Python written in Python; even the bytecode interpreter is written in Python. This is executed using CPython as the underlying interpreter. One of the goals of the project is to encourage experimentation with the language itself by making it easier to modify the interpreter (since it is written in Python). Additional information is available on the PyPy project’s home page.
Each of these implementations varies in some way from the language as documented in this manual, or introduces specific information beyond what’s covered in the standard Python documentation. Please refer to the implementation-specific documentation to determine what else you need to know about the specific implementation you’re using.