Antoine Pitrou <solip...@pitrou.net> wrote:
> On Thu, 18 Aug 2011 18:57:00 +0200
> Stefan Krah <ste...@bytereef.org> wrote:
> >
> > Oh no, the name isn't quite right then. It should be a replacement
> > for the combination PyBuffer_FillInfo()/PyMemoryView_FromBuffer()
> > and it should temporarily wrap a C-string.
>
> Ah, nice.
>
> > PyObject * PyMemoryView_FromCString(char *s, Py_ssize_t size, int flags);
>
> It's not really a C string, since it's not null-terminated.
> PyMemoryView_FromMemory?
>
> (that would mirror PyUnicode_FromUnicode, for example)
I see, yes. PyMemoryView_FromStringAndSize()? No, too much typing. I prefer
PyMemoryView_FromMemory().
> > 'flags' is just PyBUF_READ or PyBUF_WRITE.
>
> Why do we have these in addition to PyBUF_WRITABLE already?
That's a bit involved, this is how I see it:
There are four buffer *request* flags that can be sent to a buffer provider
and that indicate the amount of complexity that a consumer can handle (in
decreasing order):
PyBUF_INDIRECT -> suboffsets (PIL-style)
PyBUF_STRIDES -> strides (Numpy-style)
PyBUF_ND -> C-contiguous, but possibly multi-dimensional
PyBUF_SIMPLE -> contiguous, one-dimensional, unsigned bytes
Each of those flags can be mixed freely with two additional flags:
PyBUF_WRITABLE
PyBUF_FORMAT
All other buffer request flags are simply combinations of those.
For example, if you use PyBUF_WRITABLE as the only flag, logically
it should be seen as PyBUF_WRITABLE|PyBUF_SIMPLE (this works since
PyBUF_SIMPLE is defined as 0).
PyBUF_READ and PyBUF_WRITE are so far only used for
PyMemoryView_GetContiguous().
The PEP still has a flag named PyBUF_UPDATEIFCOPY, but that didn't make it
into object.h.
I thought it might be appropriate to use PyBUF_READ and PyBUF_WRITE
to underline the fact that you cannot send a fine grained buffer
request to PyMemoryView_FromMemory()[1]. Also, PyBUF_READ is easier
to understand than PyBUF_SIMPLE.
But I'd be equally happy with PyBUF_SIMPLE/PyBUF_WRITABLE.
Stefan Krah
[1] The terminology might sound funny, but there is a function that
can act a micro buffer provider:
int PyBuffer_FillInfo(Py_buffer *view, PyObject *obj, void *buf, Py_ssize_t len,
int readonly, int infoflags)
An exporter can use this function as a building block for a getbuffer()
method for unsigned bytes, since it reacts correctly to *all* possible
buffer requests in 'infoflags'.
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