[GitHub] [arrow-rs] kszucs commented on a change in pull request #691: PyO3 bridge for pyarrow interoperability

[GitBox <gi...@apache.org>]

kszucs commented on a change in pull request #691:
URL: https://github.com/apache/arrow-rs/pull/691#discussion_r691324674



##########
File path: arrow/src/pyarrow.rs
##########
@@ -0,0 +1,223 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+//! This library demonstrates a minimal usage of Rust's C data interface to pass
+//! arrays from and to Python.
+
+use std::convert::{From, TryFrom};
+use std::sync::Arc;
+
+use libc::uintptr_t;
+use pyo3::import_exception;
+use pyo3::prelude::*;
+use pyo3::types::PyList;
+
+use crate::array::{make_array, Array, ArrayData, ArrayRef};
+use crate::datatypes::{DataType, Field, Schema};
+use crate::error::ArrowError;
+use crate::ffi;
+use crate::ffi::FFI_ArrowSchema;
+use crate::record_batch::RecordBatch;
+
+import_exception!(pyarrow, ArrowException);
+pub type PyArrowException = ArrowException;
+
+impl From<ArrowError> for PyErr {
+    fn from(err: ArrowError) -> PyErr {
+        PyArrowException::new_err(err.to_string())
+    }
+}
+
+pub trait PyArrowConvert: Sized {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self>;
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject>;
+}
+
+impl PyArrowConvert for DataType {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        let c_schema = FFI_ArrowSchema::empty();
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        value.call_method1("_export_to_c", (c_schema_ptr as uintptr_t,))?;
+        let dtype = DataType::try_from(&c_schema)?;
+        Ok(dtype)
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        let c_schema = FFI_ArrowSchema::try_from(self)?;
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        let module = py.import("pyarrow")?;
+        let class = module.getattr("DataType")?;
+        let dtype = class.call_method1("_import_from_c", (c_schema_ptr as uintptr_t,))?;
+        Ok(dtype.into())
+    }
+}
+
+impl PyArrowConvert for Field {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        let c_schema = FFI_ArrowSchema::empty();
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        value.call_method1("_export_to_c", (c_schema_ptr as uintptr_t,))?;
+        let field = Field::try_from(&c_schema)?;
+        Ok(field)
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        let c_schema = FFI_ArrowSchema::try_from(self)?;
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        let module = py.import("pyarrow")?;
+        let class = module.getattr("Field")?;
+        let dtype = class.call_method1("_import_from_c", (c_schema_ptr as uintptr_t,))?;
+        Ok(dtype.into())
+    }
+}
+
+impl PyArrowConvert for Schema {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        let c_schema = FFI_ArrowSchema::empty();
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        value.call_method1("_export_to_c", (c_schema_ptr as uintptr_t,))?;
+        let schema = Schema::try_from(&c_schema)?;
+        Ok(schema)
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        let c_schema = FFI_ArrowSchema::try_from(self)?;
+        let c_schema_ptr = &c_schema as *const FFI_ArrowSchema;
+        let module = py.import("pyarrow")?;
+        let class = module.getattr("Schema")?;
+        let schema =
+            class.call_method1("_import_from_c", (c_schema_ptr as uintptr_t,))?;
+        Ok(schema.into())
+    }
+}
+
+impl PyArrowConvert for ArrayData {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        // prepare a pointer to receive the Array struct
+        let (array_pointer, schema_pointer) =
+            ffi::ArrowArray::into_raw(unsafe { ffi::ArrowArray::empty() });
+
+        // make the conversion through PyArrow's private API
+        // this changes the pointer's memory and is thus unsafe.
+        // In particular, `_export_to_c` can go out of bounds
+        value.call_method1(
+            "_export_to_c",
+            (array_pointer as uintptr_t, schema_pointer as uintptr_t),
+        )?;
+
+        let ffi_array =
+            unsafe { ffi::ArrowArray::try_from_raw(array_pointer, schema_pointer)? };
+        let data = ArrayData::try_from(ffi_array)?;
+
+        Ok(data)
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        let array = ffi::ArrowArray::try_from(self.clone())?;
+        let (array_pointer, schema_pointer) = ffi::ArrowArray::into_raw(array);
+
+        let module = py.import("pyarrow")?;
+        let class = module.getattr("Array")?;
+        let array = class.call_method1(
+            "_import_from_c",
+            (array_pointer as uintptr_t, schema_pointer as uintptr_t),
+        )?;
+        Ok(array.to_object(py))
+    }
+}
+
+impl PyArrowConvert for ArrayRef {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        Ok(make_array(ArrayData::from_pyarrow(value)?))
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        self.data().to_pyarrow(py)
+    }
+}
+
+impl<T> PyArrowConvert for T
+where
+    T: Array + From<ArrayData>,
+{
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        Ok(ArrayData::from_pyarrow(value)?.into())
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        self.data().to_pyarrow(py)
+    }
+}
+
+impl PyArrowConvert for RecordBatch {
+    fn from_pyarrow(value: &PyAny) -> PyResult<Self> {
+        // TODO(kszucs): implement the FFI conversions in arrow-rs for RecordBatches
+        let schema = value.getattr("schema")?;
+        let schema = Arc::new(Schema::from_pyarrow(schema)?);
+
+        let arrays = value.getattr("columns")?.downcast::<PyList>()?;
+        let arrays = arrays
+            .iter()
+            .map(ArrayRef::from_pyarrow)
+            .collect::<PyResult<_>>()?;
+
+        let batch = RecordBatch::try_new(schema, arrays)?;
+        Ok(batch)
+    }
+
+    fn to_pyarrow(&self, py: Python) -> PyResult<PyObject> {
+        let mut py_arrays = vec![];
+        let mut py_names = vec![];
+
+        let schema = self.schema();
+        let fields = schema.fields().iter();
+        let columns = self.columns().iter();
+
+        for (array, field) in columns.zip(fields) {
+            py_arrays.push(array.to_pyarrow(py)?);
+            py_names.push(field.name());
+        }
+
+        let module = py.import("pyarrow")?;
+        let class = module.getattr("RecordBatch")?;
+        let record = class.call_method1("from_arrays", (py_arrays, py_names))?;
+
+        Ok(PyObject::from(record))
+    }
+}
+
+macro_rules! add_conversion {
+    ($typ:ty) => {
+        impl<'source> FromPyObject<'source> for $typ {
+            fn extract(value: &'source PyAny) -> PyResult<Self> {
+                Self::from_pyarrow(value)
+            }
+        }
+
+        impl<'a> IntoPy<PyObject> for $typ {
+            fn into_py(self, py: Python) -> PyObject {
+                self.to_pyarrow(py).unwrap()

Review comment:
       We need to unwrap here because `IntoPy` is infallible, see https://github.com/PyO3/pyo3/issues/1813




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