[Python-Dev] PEP: Adding data-type objects to Python

[Travis Oliphant]

Martin v. Löwis wrote:
> Robert Kern schrieb:
> 
>>>As I unification mechanism, I think it is insufficient. I doubt it
>>>can express all the concepts that ctypes supports.
>>
>>What do you think is missing that can't be added?
> 
> 
> I can factually only report what is missing. Whether it can be added,
> I don't know. As I just wrote in a few other messages: pointers,
> unions, functions pointers, packed structs, incomplete/recursive
> types. Also "flexible array members" (i.e. open-ended arrays).
> 

I understand function pointers, pointers, and unions.

Function pointers are "supported" with the void data-type and could be 
more specifically supported if it were important.   People typically 
don't use the buffer protocol to send function-pointers around in a way 
that the void description wouldn't be enough.


Pointers are also "supported" with the void data-type.  If pointers to 
other data-types were an important feature to support, then this could 
be added in many ways (a flag on the data-type object for example is how 
this is done is NumPy).

Unions are actually supported (just define two fields with the same 
offset).

I don't know what you mean by "packed structs" (unless you are talking 
about alignment issues in which case there is support for it).

I'm not sure I understand what you mean by "incomplete / recursive" 
types unless you are referring to something like a node where an element 
of the structure is a pointer to another structure of the same kind 
(like used in linked-lists or trees).  If that is the case, then it's 
easily supported once support for pointers is added.

I also don't know what you mean by "open-ended arrays."  The data-format 
is meant to describe a fixed-size chunk of data.

String syntax is not needed to support all of these things.  What I'm 
asking for and proposing is a way to construct an instance of a single 
Python type that communicates this data-format information in a 
standardized way.


-Travis