[Python-Dev] Error in PEP3118?

[Guido van Rossum]

Travis,

Perhaps you can add this rationale to the PEP? It seems helpful and
might stave off future confusion.

--Guido

On Jan 23, 2008 8:17 AM, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> Thomas Heller wrote:
> > Hi Travis,
> >
> > The pep contains this sample:
> >
> > """
> > Nested array
> >     ::
> >
> >         struct {
> >              int ival;
> >              double data[16*4];
> >         }
> >         """i:ival:
> >            (16,4)d:data:
> >         """
> > """
> >
> > I think it is wrong and must be changed to the following; is this correct?
> >
> > """
> > Nested array
> >     ::
> >
> >         struct {
> >              int ival;
> >              double data[16][4];
> >         }
> >         """i:ival:
> >            (16,4)d:data:
> >         """
> > """
>
> I responded off list to this email and wanted to summarize my response
> for others to peruse.
>
> Basically,  the answer is that the struct syntax proposed for
> multi-dimensional arrays is not intended to mimic how the C-compiler
> handles statically defined C-arrays (i.e. the pointer-to-pointers style
> of multi-dimensional arrays).  It is intended to handle the
> contiguous-block-of-data style of multi-dimensional arrays that NumPy uses.
>
> I wanted to avoid 2-d static arrays in the examples because it gets
> confusing and AFAIK the layout of the memory for a double data[16][4] is
> the same as data[16*4].  The only difference is how the C-compiler
> translates data[4][3] and data[4].
>
> The intent of the struct syntax is to handle describing memory.  The
> point is not to replicate how the C-compiler deals with statically
> defined N-D arrays.  Thus, even though the struct syntax allows
> *communicating* the intent of a contiguous block of memory inside a
> structure as an N-d array, the fundamental memory block is the
> equivalent of a 1-d array in C.
>
> So, I think the example is correct (and intentional).
>
> -Travis O.
>
>
>
>
>
>
>
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-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)