c_bool type not supported for BigEndianStructure on little-endian machine

[HassanElKarouni]

BPO	30510
Nosy	@terryjreedy, @iritkatriel
Files	c_bool_bug.py: example of bug init.py: patched file solving problem

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-05-30.10:35:54.469>
labels = ['ctypes', 'build', '3.11']
title = 'c_bool type not supported for BigEndianStructure on little-endian machine'
updated_at = <Date 2022-01-23.18:29:53.273>
user = 'https://bugs.python.org/HassanElKarouni'

bugs.python.org fields:

activity = <Date 2022-01-23.18:29:53.273>
actor = 'iritkatriel'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['ctypes']
creation = <Date 2017-05-30.10:35:54.469>
creator = 'Hassan El Karouni'
dependencies = []
files = ['46926', '46927']
hgrepos = []
issue_num = 30510
keywords = []
message_count = 3.0
messages = ['294747', '295063', '411394']
nosy_count = 3.0
nosy_names = ['terry.reedy', 'Hassan El Karouni', 'iritkatriel']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'compile error'
url = 'https://bugs.python.org/issue30510'
versions = ['Python 3.11']

Linked PRs

• gh-74695: Add support for ctypes.c_bool on opposite endian systems #127280

[HassanElKarouni]

When trying to create a BigEndianStructure containing a c_bool field (on a windows machine), i get the following traceback:

File "/home/elkarouh/anaconda2/lib/python2.7/ctypes/_endian.py", line 24, in _other_endian
raise TypeError("This type does not support other endian: %s" % typ)
TypeError: This type does not support other endian: <class 'ctypes.c_bool'>

I fixed the problem by patching __init__.py under the ctypes directory by adding the following two lines:

c_bool.__ctype_le__ = c_bool.__ctype_be__ = c_bool
_check_size(c_bool)

[terryjreedy]

Please post or upload minimal code that reproduces the problem for you.

[iritkatriel]

Reproduced on 3.11:

>>> from ctypes import *
>>> class r( BigEndianStructure ):
...     _fields_ = [( "d0", c_uint32),
...                 ( "d1", c_bool )
...                      ]
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/iritkatriel/src/cpython-654/Lib/ctypes/_endian.py", line 31, in __setattr__
    fields.append((name, _other_endian(typ)) + rest)
                         ^^^^^^^^^^^^^^^^^^
  File "/Users/iritkatriel/src/cpython-654/Lib/ctypes/_endian.py", line 21, in _other_endian
    raise TypeError("This type does not support other endian: %s" % typ)
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: This type does not support other endian: <class 'ctypes.c_bool'>

[encukou]

The problem with bool is that its size and the memory representations of its states are implementation-defined. For example, 0x01 might be true on one platform, but another platform might not only use 0x8000 instead, but also consider the 0x01 bit to be irrelevant padding.

For ctypes.c_bool we can assume the native representation. But for the byte-swapped version, we know it's not the native bool, and I don't think we can assume much about what it is.

If you're writing code for a specific platform, use a platform-specific type in your Structure definition -- for example, ctypes.c_ubyte if your sizeof(c_bool) == 1, which seems to be the assumption for setting c_bool.__ctype_le__ = c_bool.__ctype_be__ = c_bool.