[New-bugs-announce] [issue24859] ctypes.Structure bit order is reversed - counts from right

[zeero]

New submission from zeero:

I'm implementing a CAN SAEJ1939 stack in Python and convert CAN message ids in between integers and structures, tunneling them through a Union object with 4 bytes like what i would do in C.

I was checking that particular function and the 3 priority bits were at the wrong position. Some trials later i concluded the bits are reversed and inverted the order in my structure. Now it works fine.

I'm not sure if it's a bug but i would expect ctypes.Structure to
store the fields in the order i provide and not the other way around.
On the other hand the bytes are in the order i provided.

The System I'm running on is 64Bit Ubuntu AMD A1046 but it shows the same behaviour an a 64bit Windows 7 Intel I5

----------
components: ctypes
files: test_structure.py
messages: 248536
nosy: zeero
priority: normal
severity: normal
status: open
title: ctypes.Structure bit order is reversed - counts from right
type: behavior
versions: Python 3.4
Added file: http://bugs.python.org/file40174/test_structure.py

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue24859>
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