[Pyrex] Allocating an array.array of a specific length in pyrex

[Chris Lambacher]

I replaced:
a = array.array('B', , [0] * (pixels * 2))
with:
a = PyString_FromStringAndSize(NULL, pixels * 2)

and got:
C:\work\testing\plink_o_ip>python ycbycr.py
Traceback (most recent call last):
  File "ycbycr.py", line 62, in ?
    ycbycr = image2ycbycr(im)
  File "ycbycr.py", line 38, in image2ycbycr
    return _ycbycr.ycbcr2ycbycr(w, h, ycbcrim.tostring())
  File "_ycbycr.pyx", line 42, in _ycbycr.ycbcr2ycbycr
    res = get_w_buffer(a, &out_str, &buffer_len)
TypeError: Cannot use string as modifiable buffer

Strings are not mutable so this is not going to work for me :(

Is there a way to allocate a python buffer object and give that to
array.array or a string object?

-Chris

On 6/8/05, Chris Lambacher <lambacck at gmail.com> wrote:
> The memory is not temporary, I am passing it out as an array, thus the
> malloc/free route will require double allocation(once for malloc/free,
> once for array.array).  I am not using string because when I tried to
> pass the data in as string, pyrex complained about the conversion.
> However, I could probably use the same PyObject_AsReadBuffer function
> call to get at the data passed in to the function as a string and then
> pass it out as a string as well using the interface suggested (
> PyString_FromStringAndSize and PyString_AsString ).  Perhapse I need
> to substitute PyObject_AsWriteBuffer instead of PyString_AsString in
> order for my changes to get propegated back to the string object?
> 
> -Chris
> 
> 
> On 6/8/05, Adam Langley <alangley at gmail.com> wrote:
> > On 6/8/05, Chris Lambacher <lambacck at gmail.com> wrote:
> > > My question is, is there a better way to
> > > allocate the memory for the array.array object than:
> > >       a = array.array('B', [0] * (pixels * 2))
> >
> > cdef unsigned char *buffer
> > temp_string = PyString_FromStringAndSize(NULL, length)
> > buffer = <unsigned char *> PyString_AsString(temp_string)
> >
> > That's one way to do it. But it looks like you just want an area of
> > memory so why not:
> >
> > cdef extern from "stdlib.h":
> >   ctypedef unsigned long size_t
> >   void *malloc(size_t size)
> >   void free(void *mem)
> >
> > ?
> >
> > AGL
> >
> > --
> > Adam Langley                                      agl at imperialviolet.org
> > http://www.imperialviolet.org                       (+44) (0)7906 332512
> > PGP: 9113   256A   CC0F   71A6   4C84   5087   CDA5   52DF   2CB6   3D60
> >
> 
> 
> --
> Christopher Lambacher
> lambacck at computer.org
> 


-- 
Christopher Lambacher
lambacck at computer.org