Travis Oliphant schrieb: > Greg Ewing wrote: >> Travis Oliphant wrote: >> >> >>>Part of the problem is that ctypes uses a lot of different Python types >>>(that's what I mean by "multi-object" to accomplish it's goal). What >>>I'm looking for is a single Python type that can be passed around and >>>explains binary data. >> >> >> It's not clear that multi-object is a bad thing in and >> of itself. It makes sense conceptually -- if you have >> a datatype object representing a struct, and you ask >> for a description of one of its fields, which could >> be another struct or array, you would expect to get >> another datatype object describing that. >> >> Can you elaborate on what would be wrong with this? >> >> Also, can you clarify whether your objection is to >> multi-object or multi-type. They're not the same thing -- >> you could have a data structure built out of multiple >> objects that are all of the same Python type, with >> attributes distinguishing between struct, array, etc. >> That would be single-type but multi-object. > > I've tried to clarify this in another post. Basically, what I don't > like about the ctypes approach is that it is multi-type (every new > data-format is a Python type). > > In order to talk about all these Python types together, then they must > all share some attribute (or else be derived from a meta-type in C with > a specific function-pointer entry).
(I tried to read the whole thread again, but it is too large already.) There is a (badly named, probably) api to access information about ctypes types and instances of this type. The functions are PyObject_stgdict(obj) and PyType_stgdict(type). Both return a 'StgDictObject' instance or NULL if the funtion fails. This object is the ctypes' type object's __dict__. StgDictObject is a subclass of PyDictObject and has fields that carry information about the C type (alignment requirements, size in bytes, plus some other stuff). Also it contains several pointers to functions that implement (in C) struct-like functionality (packing/unpacking). Of course several of these fields can only be used for ctypes-specific purposes, for example a pointer to the ffi_type which is used when calling foreign functions, or the restype, argtypes, and errcheck fields which are only used when the type describes a function pointer. This mechanism is probably a hack because it'n not possible to add C accessible fields to type objects, on the other hand it is extensible (in principle, at least). Just to describe the implementation. Thomas _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
