gh-76961: Fix the PEP3118 format string for ctypes.Structure by eric-wieser · Pull Request #5561 · python/cpython (original) (raw)

This LGTM, and behaves as expected in my manual testing; the code looks good. I left a couple of nitpick-level comments / suggestions.

@abalkin This is still assigned to you; is there anything you're aware of that would mean this shouldn't be merged?

The issue is marked as a "bug" (which makes some sense), but I think this is sufficiently new-feature'y that the changes shouldn't be backported to Python <3.12. @abalkin: thoughts?

The way we build up the format string doesn't seem ideal - it looks as though it would take time quadratic in the number of fields of the struct. But AFAICT that's a pre-existing issue, not introduced in this PR. Presumably for the sort of things for which this is used in practice this hasn't yet been a real issue.

Observation: it seems there's no documentation of the "data format description" language outside PEP 3118 itself, unless I'm missing something. I'd expect the ctypes documentation to at least have a pointer to PEP 3118 (though it would be better to have a description in the docs themselves at some point, since PEPs are historical documents that shouldn't generally by relied upon to be up to date with implementations.) Anyway, that's off-topic for this PR.