[New-bugs-announce] [issue4270] struct module: pack/unpack and byte order on x86_64

[Mikhail Terekhov]

New submission from Mikhail Terekhov <termim at gmail.com>:

pack/unpack behavior changes unexpectedly depending on the byte order:

l:/tmp >uname -pmiovs
Linux #1 SMP 2008-10-14 22:17:43 +0200 x86_64 x86_64 x86_64 GNU/Linux
l:/tmp >python
python
Python 2.5.1 (r251:54863, Aug  1 2008, 00:35:20) 
[GCC 4.2.1 (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import struct
import struct
>>> struct.pack(">L",0xdeadbeef)
struct.pack(">L",0xdeadbeef)
'\xde\xad\xbe\xef'
>>> struct.pack("L",0xdeadbeef)
struct.pack("L",0xdeadbeef)
'\xef\xbe\xad\xde\x00\x00\x00\x00'
>>> struct.pack("<L",0xdeadbeef)
struct.pack("<L",0xdeadbeef)
'\xef\xbe\xad\xde'
>>> 

The length of the result above is 8 when no byte order is specified
and 4 when it is.

Another example:

>>> struct.pack("L",0xdeadbeef00000000)
'\x00\x00\x00\x00\xef\xbe\xad\xde'
>>> struct.pack("<L",0xdeadbeef00000000)
'\x00\x00\x00\x00'
>>> struct.pack("!L",0xdeadbeef00000000)
'\x00\x00\x00\x00'
>>> struct.pack("!L",0x12345678deadbeef)
'\xde\xad\xbe\xef'
>>> struct.pack("L",0x12345678deadbeef)
'\xef\xbe\xad\xdexV4\x12'
>>> 

Last results look strange.

----------
components: Library (Lib)
messages: 75569
nosy: mmm77
severity: normal
status: open
title: struct module: pack/unpack and byte order on x86_64
type: behavior
versions: Python 2.5

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue4270>
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