[Python-Dev] PEP 3118: Extended buffer protocol (new version)

[Travis Oliphant]

Greg Ewing wrote:
> From PEP 3118:
>
>   A memory-view object is an extended buffer object that
>   should replace the buffer object in Python 3K.
>
>   typedef struct {
>     PyObject_HEAD
>     PyObject *base;
>     struct bufferinfo view;
>     int itemsize;
>     int flags;
>   } PyMemoryViewObject;
>
> If the purpose is to provide Python-level access to an
> object via its buffer interface, then keeping a bufferinfo
> struct in it is the wrong implementation strategy, since it
> implies keeping the base object's memory locked as long as
> the view object exists.

Yes, but that was the intention.   The MemoryView Object is basically an 
N-d array object. 
>
> That was the mistake made by the original buffer object,
> and the solution is not to hold onto the info returned by
> the base object's buffer interface, but to make a new
> buffer request for each Python-level access.
I could see this approach also, but if we went this way then the memory 
view object should hold "slice" information so that it can be a "sliced" 
view of a memory area.

Because slicing NumPy array's already does it by holding on to a view, I 
guess having an object that doesn't hold on to a view in Python but 
"re-gets" it every time it is needed, would be useful. 

In that case:

typedef struct {
    PyObject_HEAD
    PyObject *base;
    int ndims;
    PyObject **slices;  /* or 3 Py_ssize_t arrays */
    int flags;
} PyMemoryViewObject;

would be enough to store, I suppose.


-Travis