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Length of struct.pack('HL', 1,1) incorrect (8 instead of 6 bytes) #47731

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dparolin mannequin opened this issue Aug 1, 2008 · 2 comments
Closed

Length of struct.pack('HL', 1,1) incorrect (8 instead of 6 bytes) #47731

dparolin mannequin opened this issue Aug 1, 2008 · 2 comments
Labels
stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error

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@dparolin
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Mannequin

dparolin mannequin commented Aug 1, 2008

BPO 3481
Nosy @amauryfa

Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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GitHub fields:

assignee = None
closed_at = <Date 2008-08-01.00:40:32.380>
created_at = <Date 2008-08-01.00:17:05.150>
labels = ['invalid', 'type-bug', 'library']
title = "Length of struct.pack('HL', 1,1) incorrect (8 instead of 6 bytes)"
updated_at = <Date 2008-08-01.00:40:32.122>
user = 'https://bugs.python.org/dparolin'

bugs.python.org fields:

activity = <Date 2008-08-01.00:40:32.122>
actor = 'amaury.forgeotdarc'
assignee = 'none'
closed = True
closed_date = <Date 2008-08-01.00:40:32.380>
closer = 'amaury.forgeotdarc'
components = ['Library (Lib)']
creation = <Date 2008-08-01.00:17:05.150>
creator = 'dparolin'
dependencies = []
files = []
hgrepos = []
issue_num = 3481
keywords = []
message_count = 2.0
messages = ['70535', '70536']
nosy_count = 2.0
nosy_names = ['amaury.forgeotdarc', 'dparolin']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue3481'
versions = ['Python 2.5', 'Python 2.4']
@dparolin
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dparolin mannequin commented Aug 1, 2008

Python Versions tested:
Windows 2.5.2 (r252:60911)
Debian Linux Python 2.4.4

Example:
>>> import struct
>>> struct.pack('HL', 1, 1)

results in '\x01\x00\x00\x00\x01\x00\x00\x00'
although '\x01\x00\x01\x00\x00\x00' was expected.

if concatenated or done separately
>>> struct.pack('H', 1) + struct.pack('L', 1)

result is as expected '\x01\x00\x01\x00\x00\x00'
or
'\x01\x00' and '\x01\x00\x00\x00' respectively

Error:
Length is 8 where it should be 6
This is as well true for "hl", "hL" and "Hl".

Free description:
I could not find another error regarding that, nor any information using
popular search.
Further no explanation found why that might be valid behaviour.

Regards,
Dominique

@dparolin dparolin mannequin added stdlib Python modules in the Lib dir type-bug An unexpected behavior, bug, or error labels Aug 1, 2008
@amauryfa
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amauryfa commented Aug 1, 2008

The struct module is correct.
You see here the result of "alignment": the address of a long is always
a multiple of the size of a long.

The struct module mimics the C compiler: a "struct { short x; long y;
}", will actually occupy 8 bytes in memory (on a 32bit processor).
There are two padding bytes, that are not used.

@amauryfa amauryfa closed this as completed Aug 1, 2008
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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