[Jython-dev] Buffer API

[Jeff A. <ja...@fa...>]

In the implementation of bytearray for Jython, I used the C source 
extensively to understand the intended behaviour. I observed that 
CPython makes heavy use of the Buffer API in bytearrayobject.c. In fact, 
the answer to "what type is this argument" is frequently "anything 
supporting the buffer API".

Earlier this year, Jim Baker contributed an outline "MemoryView" to the 
Jython code base intended to fill this role, but not enough to use 
directly, or for me at the time, even to see how it should develop. 
PyByteArray therefore uses a "View" wrapper, where needed around 
arguments of well-known type, that provides privately to bytearray many 
of the benefits of the buffer API. But Jython's bytearray will never 
really be finished while a new type can come along that (in CPython) 
presents the buffer API. And now, it turns out, code in other modules 
needs to access bytearray through the expected buffer API.

So I bit the bullet, and propose to implement a Java-flavour of the 
buffer API that I will put on PyByteArray and PyString. It will 
certainly work for one-dimensional byte arrays, and is faithful enough 
to CPython design (taking the hint from Jim's work) that I think it 
would work for NumPy and PIL-style arrays but I don't intend to 
implement a support class for those. My homework is here on the wiki:
http://wiki.python.org/jython/BufferProtocol

I'm going to claim contributor's rights on questions of taste and style, 
but does anyone out there, especially anyone who has followed 
development of the CPython buffer API,  or put it to sophisticated use, 
see a massive pitfall?

Jeff Allen