paleolimbot commented on code in PR #378:
URL: https://github.com/apache/arrow-nanoarrow/pull/378#discussion_r1483607901
##########
python/src/nanoarrow/_lib.pyx:
##########
@@ -176,6 +178,188 @@ cdef object alloc_c_array_shallow_copy(object base, const
ArrowArray* c_array) n
return array_capsule
+cdef void pycapsule_buffer_deleter(object stream_capsule) noexcept:
+ cdef ArrowBuffer* buffer = <ArrowBuffer*>PyCapsule_GetPointer(
+ stream_capsule, 'nanoarrow_buffer'
+ )
+
+ ArrowBufferReset(buffer)
+ ArrowFree(buffer)
+
+
+cdef object alloc_c_buffer(ArrowBuffer** c_buffer) noexcept:
+ c_buffer[0] = <ArrowBuffer*> ArrowMalloc(sizeof(ArrowBuffer))
+ ArrowBufferInit(c_buffer[0])
+ return PyCapsule_New(c_buffer[0], 'nanoarrow_buffer',
&pycapsule_buffer_deleter)
+
+cdef void c_deallocate_pybuffer(ArrowBufferAllocator* allocator, uint8_t* ptr,
int64_t size) noexcept with gil:
+ cdef Py_buffer* buffer = <Py_buffer*>allocator.private_data
+ PyBuffer_Release(buffer)
+ ArrowFree(buffer)
+
+
+cdef ArrowBufferAllocator c_pybuffer_deallocator(Py_buffer* buffer):
+ # This should probably be changed in nanoarrow C; however, currently, the
deallocator
+ # won't get called if buffer.buf is NULL.
+ if buffer.buf == NULL:
+ PyBuffer_Release(buffer)
+ return ArrowBufferAllocatorDefault()
+
+ cdef Py_buffer* allocator_private =
<Py_buffer*>ArrowMalloc(sizeof(Py_buffer))
+ if allocator_private == NULL:
+ PyBuffer_Release(buffer)
+ raise MemoryError()
+
+ memcpy(allocator_private, buffer, sizeof(Py_buffer))
+ return
ArrowBufferDeallocator(<ArrowBufferDeallocatorCallback>&c_deallocate_pybuffer,
allocator_private)
+
+
+cdef c_arrow_type_from_format(format):
+ # PyBuffer_SizeFromFormat() was added in Python 3.9 (potentially faster)
+ item_size = calcsize(format)
+
+ # Don't allow non-native endian values
+ if sys_byteorder == "little" and (">" in format or "!" in format):
+ raise ValueError(f"Can't convert format '{format}' to Arrow type")
+ elif sys_byteorder == "big" and "<" in format:
+ raise ValueError(f"Can't convert format '{format}' to Arrow type")
+
+ # Strip system endian specifiers
+ format = format.strip("=@")
+
+ if format == "c":
+ return 0, NANOARROW_TYPE_STRING
Review Comment:
I stole this from how numpy deals with `np.array("abcdefg")`. This
particular mapping allows `np.array("abc")` to roundtrip through a `c_buffer()`
but I don't really have any strong feelings about it.
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