Merge pull request #194 from PyO3/intopyarray-pointer-fix

Fix IntoPyArray for arrays of which the starting pointer is not equal…

Author: kngwyu

src/array.rs

@@ -415,14 +415,15 @@ impl<T: Element, D: Dimension> PyArray<T, D> {
         py: Python<'py>,
         dims: ID,
         strides: *const npy_intp,
-        slice: Box<[T]>,
+        boxed_slice: Box<[T]>,
+        data_ptr: Option<*const T>,
     ) -> &'py Self
     where
         ID: IntoDimension<Dim = D>,
     {
         let dims = dims.into_dimension();
-        let container = SliceBox::new(slice);
-        let data_ptr = container.data.as_ptr();
+        let container = SliceBox::new(boxed_slice);
+        let data_ptr = data_ptr.unwrap_or_else(|| container.data.as_ptr());
         let cell = pyo3::PyClassInitializer::from(container)
             .create_cell(py)
             .expect("Object creation failed.");

src/convert.rs

@@ -39,7 +39,7 @@ impl<T: Element> IntoPyArray for Box<[T]> {
     fn into_pyarray<'py>(self, py: Python<'py>) -> &'py PyArray<Self::Item, Self::Dim> {
         let len = self.len();
         let strides = [mem::size_of::<T>() as npy_intp];
-        unsafe { PyArray::from_boxed_slice(py, [len], strides.as_ptr(), self) }
+        unsafe { PyArray::from_boxed_slice(py, [len], strides.as_ptr(), self, None) }
     }
 }
 
@@ -59,10 +59,20 @@ where
     type Item = A;
     type Dim = D;
     fn into_pyarray<'py>(self, py: Python<'py>) -> &'py PyArray<Self::Item, Self::Dim> {
-        let strides = self.npy_strides();
-        let dim = self.raw_dim();
-        let boxed = self.into_raw_vec().into_boxed_slice();
-        unsafe { PyArray::from_boxed_slice(py, dim, strides.as_ptr(), boxed) }
+        let (strides, dim) = (self.npy_strides(), self.raw_dim());
+        let orig_ptr = self.as_ptr();
+        let is_empty_or_size0 = self.is_empty() || std::mem::size_of::<Self>() == 0;
+        let vec = self.into_raw_vec();
+        let offset = if is_empty_or_size0 {
+            0
+        } else {
+            unsafe { orig_ptr.offset_from(vec.as_ptr()) as usize }
+        };
+        let mut boxed_slice = vec.into_boxed_slice();
+        // data_ptr is not always the pointer to the 1st element.
+        // See https://github.com/PyO3/rust-numpy/issues/182 for the detail.
+        let data_ptr = unsafe { boxed_slice.as_mut_ptr().add(offset) };
+        unsafe { PyArray::from_boxed_slice(py, dim, strides.as_ptr(), boxed_slice, Some(data_ptr)) }
     }
 }
 

tests/to_py.rs

@@ -115,6 +115,19 @@ fn into_pyarray_cant_resize() {
     })
 }
 
+/// Check that into_pyarray works for ndarray of which the pointer of the first element is
+/// not at the start. See https://github.com/PyO3/rust-numpy/issues/182 for more
+#[test]
+fn into_pyarray_collapsed() {
+    let mut arr = Array2::<f64>::from_shape_fn([3, 4], |(i, j)| (i * 10 + j) as f64);
+    arr.slice_collapse(s![1.., ..]);
+    let copy = arr.clone();
+    pyo3::Python::with_gil(|py| {
+        let py_arr = arr.into_pyarray(py);
+        assert_eq!(py_arr.readonly().as_array(), copy);
+    })
+}
+
 #[test]
 fn forder_to_pyarray() {
     pyo3::Python::with_gil(|py| {