[Python-Dev] buffer object
Guido van Rossum
Sun, 07 May 2000 17:29:43 -0400
> Forgive me for rewinding this to the very beginning. But what is a
> buffer object usefull for? I'm trying think about buffer object in terms
> of jpython, so my primary interest is the user experience of buffer
> Please correct my misunderstandings.
> - There is not a buffer protocol exposed to python object (in the way
> the sequence protocol __getitem__ & friends are exposed).
> - A buffer object typically gives access to the raw bytes which
> under lays the backing object. Regardless of the structure of the
> - It is only intended for object which have a natural byte storage to
> implement the buffer interface.
> - Of the builtin object only string, unicode and array supports the
> buffer interface.
And the new mmap module.
> - When slicing a buffer object, the result is always a string regardless
> of the buffer object base.
> In jpython, only byte arrays like jarrays.array('b', [0,1,2]) can be
> said to have some natural byte storage. The jpython string type doesn't.
> It would take some awful bit shifting to present a jpython string as an
> array of bytes.
I don't recall why JPython has jarray instead of array -- how do they
differ? I think it's a shame that similar functionality is embodied
in different APIs.
> Would it make any sense to have a buffer object which only accept a byte
> array as base? So that jpython would say:
> >>> buffer("abc")
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> TypeError: buffer object expected
> Would it make sense to tell python users that they cannot depend on the
> portability of using strings (both 8bit and 16bit) as buffer object
I think that the portability of many string properties is in danger
with the Unicode proposal. Supporting this in the next version of
JPython will be a bit tricky.
> Because it is so difficult to look at java storage as a sequence of
> bytes, I think I'm all for keeping the buffer() builtin and buffer
> object as obscure and unknown as possible <wink>.
I basically agree, and in a private email to Greg Stein I've told him
this. I think that the array module should be promoted to a built-in
function/type, and should be the recommended solution for data
storage. The buffer API should remain a C-level API, and the buffer()
built-in should be labeled with "for experts only".
--Guido van Rossum (home page: http://www.python.org/~guido/)