On Thursday 20 September 2007 11:19, Paul Hankin wrote:
>> I suppose I could get the relevant source from the 2.5 source and compile
>> it as a custom package, but that wouldn't be very transparent for my
>> users, and would probably be getting in way over my head. :)
>>
>> Ideas? Suggestions?
>
> Here's a wrapped pack:
>
> import struct
>
> pack_double_workaround = {
> 'inf': struct.pack('Q', 0x7ff0000000000000L),
> '-inf': struct.pack('Q', 0xfff0000000000000L),
> 'nan': struct.pack('Q', 0x7ff8000000000000L)
> }
>
> def pack_one_safe(f, a):
> if f == 'd' and str(f) in pack_double_workaround:
> return pack_double_workaround[str(f)]
> return struct.pack(f, a)
>
> def pack(fmt, *args):
> return ''.join(pack_one_safe(f, a) for f, a in zip(fmt, args))
>
> Unpacking is similar: unpack doubles with 'Q' and test the
> long for equality with +-inf, and find nan's by checking bits
> 52 to 62. If the number's ok, unpack again using 'd'.
>
> You can get python values for nan, -inf and inf by using
> float('nan'), float('-inf'), float('inf').
>
> I've not been able to properly test this, as struct seems
> to work fine in Python 2.3 and 2.4 on MacOS X.
Thanks for the ideas, Paul! I came up with something that works for me, but
this has a few ideas that I'm going to implement in my wrapper to make for
cleaner code.
As to testing it on MacOS X: yeah, it can be a somewhat system-dependent
problem, so may not show up on all architectures.
Thanks for the tips!
j
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