[Python-Dev] PEP: Adding data-type objects to Python (original) (raw)

Travis Oliphant oliphant.travis at ieee.org
Mon Oct 30 23:00:49 CET 2006

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

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