kylebarron commented on issue #5067:
URL: https://github.com/apache/arrow-rs/issues/5067#issuecomment-1807204531
I took a quick stab at this but got stuck. In particular, I tried:
```rs
use arrow::array::ArrayData;
use arrow::ffi;
use pyo3::exceptions::{PyTypeError, PyValueError};
use pyo3::prelude::*;
use pyo3::types::{PyCapsule, PyTuple};
use pyo3::{PyAny, PyResult};
pub fn pyobj_to_array(ob: &'_ PyAny) -> PyResult<ArrayData> {
if ob.hasattr("__arrow_c_array__")? {
let tuple = ob.getattr("__arrow_c_array__")?.call0()?;
if !tuple.is_instance_of::<PyTuple>() {
return Err(PyTypeError::new_err(
"Expected __arrow_c_array__ to return a tuple.",
));
}
let schema_capsule = tuple.get_item(0)?;
if !schema_capsule.is_instance_of::<PyCapsule>() {
return Err(PyTypeError::new_err(
"Expected __arrow_c_array__ first element to be PyCapsule.",
));
}
let schema_capsule: &PyCapsule =
PyTryInto::try_into(schema_capsule)?;
let schema_capsule_name = schema_capsule.name()?;
if schema_capsule_name.is_none() {
return Err(PyValueError::new_err(
"Expected PyCapsule to have name set.",
));
}
let schema_capsule_name = schema_capsule_name.unwrap().to_str()?;
if schema_capsule_name != "arrow_schema" {
return Err(PyValueError::new_err(
"Expected name 'arrow_schema' in PyCapsule.",
));
}
let array_capsule = tuple.get_item(1)?;
if !array_capsule.is_instance_of::<PyCapsule>() {
return Err(PyTypeError::new_err(
"Expected __arrow_c_array__ second element to be PyCapsule.",
));
}
let array_capsule: &PyCapsule = PyTryInto::try_into(array_capsule)?;
let array_capsule_name = array_capsule.name()?;
if array_capsule_name.is_none() {
return Err(PyValueError::new_err(
"Expected PyCapsule to have name set.",
));
}
let array_capsule_name = array_capsule_name.unwrap().to_str()?;
if array_capsule_name != "arrow_array" {
return Err(PyValueError::new_err(
"Expected name 'arrow_array' in PyCapsule.",
));
}
let arr = unsafe {
ffi::from_ffi(
*array_capsule.reference::<ffi::FFI_ArrowArray>(),
schema_capsule.reference::<ffi::FFI_ArrowSchema>(),
)
.unwrap()
};
return Ok(arr);
}
Err(PyValueError::new_err(
"Expected an object with dunder __arrow_c_array__",
))
}
```
but this doesn't work because of
```
error[E0507]: cannot move out of a shared reference
--> src/ffi2.rs:60:17
|
60 | *array_capsule.reference::<ffi::FFI_ArrowArray>(),
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ move
occurs because value has type `arrow::ffi::FFI_ArrowArray`, which does not
implement the `Copy` trait
```
This has a different setup because instead of provisioning FFI structs
ourselves for python to export into, python exports its _own_ ffi structs
inside the capsule. Maybe I'm missing something in the pyo3 api to get an owned
pointer, but I assume that's not possible.
I figure here that the arrow-rs ffi code would need to be changed to allow a
reference to a `FFI_ArrowArray` struct, just like it does with the schema? It
would then just have to check that `released` on the struct is not `true`
before importing..?
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