Feature or enhancement

Proposal:

When creating actypes.Structure to map data from c/c++ to python, I have been coming up against issues where I have a structure which has an alignment due to a#pragma align.
Currently there is no way to define actypes.Structure which can map to an object like this.

I propose we add an_align_ attribute to thectypes.Structure class which will instruct the code how to align the structure itself in memory.
In the way that the_pack_ attribute indicates themaximum alignment of the fields in the struct, this would indicate theminimum alignment of the struct itself.

An example of such a struct and it's use is as follows:

importctypesclassIDString(ctypes.Structure):_align_=0x10_fields_= [        ("string",ctypes.c_char*0x10),    ]classmain(ctypes.Structure):_fields_= [        ("first",ctypes.c_uint32),        ("second",ctypes.c_ubyte),        ("string",IDString),    ]data=bytearray(b"\x07\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"b"\x68\x65\x6c\x6c\x6f\x20\x77\x6f\x72\x6c\x64\x21\x00\x00\x00\x00")m=main.from_buffer(data)print(f"first:{m.first}")# first: 7print(f"second:{m.second}")# second: 1print(f"string:{m.string.string}")# string: b'hello world!'

Without the_align_ attribute the value ofm.string.string would just be an emptybytes object since it would be reading from 8 bytes into thebytearray.

I have already made a (preliminary) implementation of thishere.

Because the attribute is optional, I believe there are no potential backward compatibility issues as the default alignment will simply be what it was before (ie. 1).

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/add-ability-to-force-alignment-of-ctypes-structure/39109

Linked PRs

• gh-112433: Add optional _align_ attribute to ctypes.Structure #113790
• gh-112433 Docs: Add versionadded value and whatsnew snippet #125087
• [3.13] gh-112433 add versionadded forctypes.Structure._align_ (GH-125087) #125113