[Numpy-discussion] numpy, Py_ssize_t, cython and 64 bits python 2.4

Robert Kern robert.kern@gmail....
Sun Nov 9 15:17:17 CST 2008

On Sun, Nov 9, 2008 at 14:01, Charles R Harris
<charlesr.harris@gmail.com> wrote:
> On Sun, Nov 9, 2008 at 11:44 AM, David Cournapeau <cournape@gmail.com>
> wrote:
>> On Mon, Nov 10, 2008 at 2:40 AM, Charles R Harris
>> <charlesr.harris@gmail.com> wrote:
>> >
>> >
>> > Let me see if I understand this correctly. For Python < 2.5 the list
>> > indices
>> > and such are ints, while for later versions they are Py_ssize_t, which
>> > is
>> > larger on 64 bit systems. Meanwhile, Py_intptr_t is large enough to hold
>> > a
>> > pointer.
>> yes
>> > So why are these two numbers being mixed?
>> It is note that they are being mixed, but that cython does not support
>> this configuration: it has a internal check which raise an exception
>> in such a case. See around line 55:
>> http://hg.cython.org/cython/file/764f1578df40/Cython/Includes/numpy.pxd
>> As I understand, this means you can't use cython for such a
>> configuration, but I just wanted to confirm whether there were known
>> workarounds.
> Lessee,
> cdef extern from "Python.h":
>      ctypedef int Py_intptr_t
> cdef extern from "numpy/arrayobject.h":
>      ctypedef Py_intptr_t npy_intp
> So they are screwing with the npy_intp type. They should hang.

Chuck, you're being rude. This would be somewhat mitigated (at least
from my perspective) if you knew what you are talking about. However,
it appears that you don't.

For integer types, the exact ctypedefs don't actually matter. The same
code would probably be generated if you used "short", even. All these
do is tell Cython to convert them to/from a Python int if they cross
the Python boundary.

> Numpy is
> numpy, Python is python, and never the two should meet. Note that none of
> this crap is in the c_numpy.pxd included with numpy, BTW. I'd send the
> cython folks a note and tell them to knock it off, the Py_* values are
> irrelevant to numpy.

And this is entirely irrelevant to the problem at hand.

David, this exception is explicitly raised in __getbuffer__() defined
in numpy.pxd. It is a Cython limitation. Cython's buffer support
cannot be used with numpy in Python < 2.5 currently. Ask Dag about it.

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco

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