gh-128715: Expose ctypes.CField, with info attributes #128950
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| # Do not use CField outside ctypes, yet. | ||
| # The constructor is internal API and may change without warning. | ||
| _internal_use=True, |
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I think this is something that pytest does a lot but how about naming it _cpython=True to stress that it's tied to CPython implementation?
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Not really -- if there's another implementation of ctypes I'd prefer that they use _internal_use too :)
| expected_size = (field.bit_size << 16) + offset_for_size | ||
| self.assertEqual(field.size, expected_size) | ||
| else: | ||
| # size == byte_size |
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I don't know if you used === above to not uncomment by mistake, so maybe size === byte_size as well? (or maybe the === was a typo)
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Wow, good eye :)
Above it's not a guard against uncommenting; I meant something like ≡ -- they're always the same. Here, the else case is where they're equal.
(The comments don't communicate that well, but, it doesn't really matter. The next person can make them consistent if they prefer that.)
| "bit field %R size too large, got %zd", | ||
| name, byte_size); | ||
| } | ||
| bitfield_size = PyLong_AsSsize_t(bit_size_obj); |
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Note for myself: because bit_size_obj should be small, we would use a fast path so this call would be efficient. However, if it's too large, then it will be slower, but we don't care as we will raise an exception.
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This is class creation. I'm leaving optimizations to PGO :)
Expose the type of struct/union field descriptors (
_ctypes._CField) asctypes.CField. (This is mainly to make it easier to refer to it -- for typing and documentation. CreatingCFields manually is not supported.)Add attributes for easier introspection:
name&type, as defined in_fields_byte_size&byte_offset, specify the chunk of memory to read/writebit_size&bit_offset, which specify the shift & mask for bitfieldsis_bitfield&is_anonymousbooleansThe existing
offsetremains, as an alias forbyte_offset.The existing
sizeis unchanged. Usually it is the same asbyte_size, but for bitfields, it contains a bit-packed combination ofbit_size&bit_offset.Update the
repr()ofCField.Use the same values internally as well. (Except
bit_size, which might overflowPy_ssize_tfor very large types. Instead, in C usebitfield_size, which is 0 for non-bitfields and thus serves asis_bitfieldflag. Different name used clarity.)Old names are removed from the C implementation to ensure a clean transition.
For simplicity, I keep
byte_sizeinCFieldObjectfor now, even though it's redundant: it's the size of the underlying type.Add a generic test that ensures the values are consistent, and that we don't have overlapping fields in structs. Use this check throughout
test_ctypes, wherever a potentially interesting Structure or Union is created. (Tests for how simple structs behave after they're created don't need the checks, but I erred on the side of adding checks.)Lift the restriction on maximum field size that was temporarily added in GH-126938. The max size is now
Py_ssize_t.This PR does not yet touch
cfield.cgetters & setters: the bit-packed “size” argument is computed and passed to those.📚 Documentation preview 📚: https://cpython-previews--128950.org.readthedocs.build/