using expy to extend python
lanyjie at yahoo.com
Thu Aug 6 01:05:41 CEST 2009
The expy project provides an express way to extend Python. After some careful considerations, I came up with some reasons for expy (this is not an exhaustive list):
(I). WYSIWYG. The expy project enables you to write your module in Python the way your extension would be (WYSIWYG), and meanwhile write your implementation in pure C. You specify your modules, functions, methods, classes, and even their documentations the usual way of writing your Python correspondences. Then your provide your implementation to the functions/methods by returning a multi-line string. By such an arrangement, everything falls in its right place, and your extension code becomes easy to read and maintain. Also, the generated code is very human-friendly.
(II). You only provide minimal information to indicate your intension of how your module/class would function in Python. So your extension is largely independent from the Python extension API. As your interaction with the Python extension API is reduced to minimal (you only care about the functionality and logic), it is then possible that your module written in expy can be independent of changes in the extension API.
(III). The building and setup of your project can be automatically done with the distutil tool. In the tutorial, there are ample examples on how easily this is achieved.
(IV). Very light weight. The expy tool is surprisingly light weight dispite of its powerful ability, as it is written in pure Python. There is no parser or compiler for code generation, but rather the powerful reflexion mechanism of Python is exploited in a clever way to generate human-friendly codes. Currently, generating code in C is supported, however, the implementation is well modularized and code generation in other languages such as Java and C++ should be easy.
While there are already a couple of other projects trying to simply this task with different strategies, such as Cython, Pyrex and modulator, this project is unique and charming in its own way. All you need is the WYSIWYG Python file for your module extension, then expy takes care of everything else. What follows in this documentation is on how to extend Python in C using expy-cxpy: the module expy helps define your module, while module cxpy helps generate C codes for your defined module.
For more information about expy, please visit its homepage at: http://expy.sf.net/
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