ctypes._CData._b_base_ does not point to root ctypes object

Hi, I've been writing some binary interface "decoder" in python using ctypes, and one thing confuses me a bit (and also ruins some of my expectations)

The docs say:

The _b_base_ read-only member is the root ctypes object that owns the memory block.

So with this code:

import ctypes

bindata = bytearray(b"AAAABBBBCCCC")

SomeArray = ctypes.c_int * 3
class SomeData(ctypes.Structure):
    _fields_ = [
        ("asdf", SomeArray),
    ]

class FinalData(ctypes.Structure):
    _fields_ = [
        ("foo", SomeData),
    ]

x = FinalData.from_buffer(bindata)
print(x)
print(hex(ctypes.addressof(x)))
print(x._b_base_)
print()

foo = x.foo
print(foo)
print(hex(ctypes.addressof(foo)))
print(foo._b_base_)
print()

asdf = foo.asdf
print(asdf)
print(hex(ctypes.addressof(asdf)))
print(asdf._b_base_)
print()

I expect foo._b_base_ and asdf._b_base_ to point to the same FinalData object, meanwhile this is the output:

<__main__.FinalData object at 0x7f3bae3fa5d0>
0x7f3bae6985d0
None

<__main__.SomeData object at 0x7f3bae6597b0>
0x7f3bae6985d0
<__main__.FinalData object at 0x7f3bae3fa5d0>

<__main__.c_int_Array_3 object at 0x7f3bae69e450>
0x7f3bae6985d0
<__main__.SomeData object at 0x7f3bae6597b0>

So instead of root ctypes object, this returns the parent ctypes object. Is this an oversight/bug?

Python version: Python 3.14.0b2
OS: NixOS unstable

Linked PRs

• gh-152623
• gh-152706

ctypes._CData.b_base のドキュメントを読み、まず提供された reproducer を実行してください。FinalData、SomeData、SomeArray の親チェーンをたどり、関連付けられた PRs をコンテキストとして使用してください。完了とは、文書化された root-owner の動作と回帰テストのカバレッジが意図されたセマンティクスと一致することを意味します。