[Python-Dev] struct.pack inconsistencies between platforms

Sun Feb 26 13:34:24 CET 2012

On Sun, Feb 26, 2012 at 12:33, pmon mail <pmon.mail at gmail.com> wrote:
> Hi
>> I have found myself in the following troubling situation.
>> I'm running the following code on a Python 2.6.5 on Linux x86:
> Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56)
> [GCC 4.4.3] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import struct
> >>> len(struct.pack('L',0))
> 4
>> Works as expected and documented (
> http://docs.python.org/library/struct.html).
>> I'm running the same code on a MacPro (OS X 10.7.3) and I'm getting the
> following:
> Python 2.7.1 (r271:86832, Jun 16 2011, 16:59:05)
> [GCC 4.2.1 (Based on Apple Inc. build 5658) (LLVM build 23351500)] on
> darwin
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import struct
> >>> len(struct.pack('L',0))
> 8
>> Documentation clearly states that the 'L' is a 4 byte integer.
>> Is this a bug? I'm I missing something?
>>By default pack uses native size, not standard size. On a 64-bit machine:
>>> struct.pack('=L', 0)
'\x00\x00\x00\x00'
>>> struct.pack('L', 0)
'\x00\x00\x00\x00\x00\x00\x00\x00'
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