An express way to extend Python!

The name expy repeats itself in the title above, and it means just that. Why consider expy? Here are some good reasons:

(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 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.

Currently, EXPY/CXPY works with Python 2.5, 2.6. I haven’t tested with Python 2.7 or 3.x (for 3.x, need to use the code tool first, and I am not sure if the C API for 3.x has changed much, if you happen to try it out, let me know what happened).

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.

More expy resources at

Getting Help

There are several ways to get some help:

1. Email list: https://lists.sourceforge.net/mailman/listinfo/expy-help
2. Project homepage: http://expy.sf.net/
3. Forum: https://sourceforge.net/forum/forum.php?forum_id=954895

Contents:

• A Dive-In Tutorial on EXPY
  • A module with some functions
  • Insert code using tags
  • Expressions v.s. code blocks
  • Allow keywords arguments
  • Customize returned values
  • Add global attributes
  • Exception for arguments/returns
  • Functions invisible to Python
  • Use ‘rawtype’ for default values
  • Add pigtails to string arguments
• Create Extension Types
  • A Dive-in Example
  • Defining A New Extension Type
  • Adding Instance Members to Types
  • Adding Class Members to Types
  • Adding Methods to Types
  • Adding Special Methods
  • Adding Properties
  • Generate and Test the Example
  • Create Base Extension Types
  • Create Numeric Types
  • Create Mapping Types
  • Create Sequence Types
  • Create Iterator Types
  • Static array dimension
  • Exposing nested C struct
  • Writing your __init__ function
  • Warnings on Py_INCREF
  • Conclusion

Indices and tables

• Index
• Search Page