[Python-Dev] Error in PEP3118?

[Travis Oliphant]

Thomas Heller wrote:
> Travis Oliphant schrieb:
> 
>>
>> 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).
> 
> Sorry, I do not think so.  If you use a 2-d array in the example, you
> must describe it correctly.  The difference between this pep and the old
> buffer interface is that the pep allows to describe both how the compiler
> sees the memory block plus the size and layout of the memory block, while
> the old buffer interface only describes single-segment memory blocks.
> And 'double data[16][4]' *is* a single memory block containing a 2-d array,
> and *not* an array of pointers.
> 

I don't understand what you mean by "must describe it correctly".   The 
size and layout of the memory block description of the PEP is not 
supposed to be dependent on the C-compiler.  It should also be able to 
define memory as used in Fortran, C#, a file, or whatever.  So, I don't 
understand the insistence that the example use C-specific 2-d array syntax.

The example as indicated is correct.  It is true that the 2-d nature of 
the block of data is only known by Python in this example.  You could 
argue that it would be more informative by showing the C-equivalent 
structure as a 2-d array.  However, it would also create the possibility 
of confusion by implying an absolute relationship between the C-compiler 
and the type description.

Your insistence that the example is incorrect makes me wonder what point 
is not being communicated between us.  Clearly there is overlap between 
C structure syntax and the PEP syntax, but the PEP type syntax allows 
for describing data in ways that the C compiler doesn't.

I'd rather steer people away from statically defined arrays in C and 
don't want to continually explain how they are subtly different.

My perception is that you are seeing too much of a connection between 
the C-compiler and the PEP description of memory.   Perhaps that's not 
it, and I'm missing something else.

Best regards,


-Travis O.