Greg Ewing wrote:
> Travis E. Oliphant wrote:
>
>> typedef char *(*formatbufferproc)(PyObject *view, int *itemsize)
>>
>> Get the format-string of the memory using the struct-module
>> string syntax
>
> I'm not sure whether a struct-format string would be
> the most convenient form for use by C-level code, as
> it could require some tedious parsing to extract
> useful information from it.
Yes, this was the reason for my dtype object. But, I think that folks
felt it was too much, especially since the struct-style syntax is
already there in Python.
Do you have any other suggestions?
>
>> typedef PyObject *(*shapebufferproc)(PyObject *view)
>>
>> Return a 2-tuple of lists containing shape information: (shape,
>> strides).
>
> I'm also not sure about using Python data structures
> to represent this, as it will force C-level code to
> use Python API calls to pull it apart. What would be
> wrong with C array of structs containing two integers
> each?
Nothing except memory management. Now, you have to worry about
allocating and deallocating memory.
>
> The buffer API is for the use of C code, and it should
> be designed with the convenience of C code in mind.
I agree. I would like to use something besides Python objects, but
handling the memory allocation is non-trivial.
On the other hand, Python tuples are pretty simple wrappers around
integers.
> Using Python data structures unnecessarily seems like
> the wrong way to go about that.
>
> The following alternative would seem to provide most of
> the things that Travis's proposal does without involving
> Python objects:
>
> struct pybuffer_shape {
> Py_ssize_t length;
> Py_ssize_t stride;
> };
>
> typedef int (*getbufferproc)(PyObject *obj,
> void **buf, Py_ssize_t *len,
> char **format,
> struct pybuffer_shape **shape, int *ndim);
>
> /* Any of buf, format and shape may be NULL if you're
> not interested in them. */
>
Besides not allowing for the request of a "contiguous" buffer from the
object or a writeable one you are also not describing how allocation for
this array of structs will be handled.
I'm not opposed in principle. In fact, I would like to get rid of the
Python objects in the protocol (in the array_struct interface for NumPy
we have the shape and strides in an array of integers).
The memory management is the only issue.
-Travis
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