On Nov 8, 2005, at 9:59 AM, Thomas Heller wrote:

>  Nicolas Pinault <nicolasp@[...].com> writes:
> 
> > Hello,
> >
> > I need to access data structures which are in big-endian format. I
> > would like to be able to declare and use Structures which manage this
> > automaticaly.
> > A keyword could say the structure contains big-endian data. When
> > accessing this structure fields, byte ordering would be done
> > automaticaly.
> 
>  This is not the first time this request comes up, although  
>  personally I
>  never had a need for it.
> 
>  First, there are some 'Struct' modules that I know of which are  
>  based on
>  the standard Python struct module, and so can handle different byte
>  orders.  (Bob Ippolito has something called ptypes, iirc, and Just van
>  Rossum has sstruct, but I'm less sure on the name of the latter).
>  Neither of them is compatible with ctypes, afaik.

This is the ptypes that Thomas is referring to (defaults to big endian):
http://svn.red-bean.com/bob/py2app/trunk/src/macholib/ptypes.py

This is an example of structures defined with it:
http://svn.red-bean.com/bob/py2app/trunk/src/macholib/mach_o.py

The MachOHeader class in this file shows how you could set up the  
endian stuff:
http://svn.red-bean.com/bob/py2app/trunk/src/macholib/MachO.py

This code successfully reads and writes Mach-O headers of big and  
little endian, in either 32 or 64 bit flavors.  Note that several  
Mach-O headers can be in a single file (a fat binary -- or Universal  
Binary in Mac OS X terminology), so this code can read/write  
different endians in the same file.  Endian is controlled at per- 
structure granularity (each struct is written by a single struct.pack).

-bob



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