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[3.11] gh-105102: Fix nested unions in structures when the system byteorder is the opposite (GH-105106) #114205

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Merged
merged 1 commit into from
Jan 17, 2024
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[3.11] gh-105102: Fix nested unions in structures when the system byteorder is the opposite (GH-105106) #114205

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4 changes: 2 additions & 2 deletions Lib/ctypes/_endian.py
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Original file line number Diff line number Diff line change
Expand Up @@ -15,8 +15,8 @@ def _other_endian(typ):
# if typ is array
if isinstance(typ, _array_type):
return _other_endian(typ._type_) * typ._length_
# if typ is structure
if issubclass(typ, Structure):
# if typ is structure or union
if issubclass(typ, (Structure, Union)):
return typ
raise TypeError("This type does not support other endian: %s" % typ)

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19 changes: 19 additions & 0 deletions Lib/ctypes/test/test_byteswap.py
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Expand Up @@ -352,5 +352,24 @@ class TestUnion(parent):
self.assertEqual(s.point.x, 1)
self.assertEqual(s.point.y, 2)

def test_build_struct_union_opposite_system_byteorder(self):
# gh-105102
if sys.byteorder == "little":
_Structure = BigEndianStructure
_Union = BigEndianUnion
else:
_Structure = LittleEndianStructure
_Union = LittleEndianUnion

class S1(_Structure):
_fields_ = [("a", c_byte), ("b", c_byte)]

class U1(_Union):
_fields_ = [("s1", S1), ("ab", c_short)]

class S2(_Structure):
_fields_ = [("u1", U1), ("c", c_byte)]


if __name__ == "__main__":
unittest.main()
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2023-05-30-18-30-11.gh-issue-105102.SnpK04.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Allow :class:`ctypes.Union` to be nested in :class:`ctypes.Structure` when
the system endianness is the opposite of the classes.