fix accidental removal of singleton dimensions when extracting PyArrayLikeDyn<'_, T, AllowTypeChange> (#496)

Author: jakemoran

CHANGELOG.md

@@ -5,6 +5,7 @@
   - Add support for free-threaded stable abi (abi3t) from Python 3.15t+ ([#556](https://github.com/PyO3/rust-numpy/pull/556))
   - fixed free-threaded builds for 32 bit platforms from Python 3.15+ ([#556](https://github.com/PyO3/rust-numpy/pull/556))
   - Drop support for Python 3.8 ([#567](https://github.com/PyO3/rust-numpy/pull/567))
+  - fix accidental removal of singleton dimensions when extracting `PyArrayLikeDyn<'_, T, AllowTypeChange>` ([#496](https://github.com/PyO3/rust-numpy/pull/496))
 
 - v0.29.0
   - Fix PyArray_DTypeMeta definition when Py_LIMITED_API is disabled ([#532](https://github.com/PyO3/rust-numpy/pull/532))

src/array_like.rs

@@ -87,7 +87,7 @@ impl Coerce for AllowTypeChange {
 ///     let np = get_array_module(py).unwrap();
 ///     let sum_up = wrap_pyfunction!(sum_up)(py).unwrap();
 ///
-///     py_run!(py, np sum_up, r"assert sum_up((1., 2., 3.)) == 6");
+///     py_run!(py, np sum_up, r"assert sum_up(np.array([1., 2., 3.])) == 6");
 /// });
 /// ```
 ///
@@ -107,6 +107,7 @@ impl Coerce for AllowTypeChange {
 ///     let np = get_array_module(py).unwrap();
 ///     let sum_up = wrap_pyfunction!(sum_up)(py).unwrap();
 ///
+///     py_run!(py, np sum_up, r"assert sum_up(np.array([1.5, 2.5])) == 3");
 ///     py_run!(py, np sum_up, r"assert sum_up((1.5, 2.5)) == 3");
 /// });
 /// ```
@@ -150,7 +151,7 @@ where
         // If the input is already an ndarray and `TypeMustMatch` is used then no type conversion
         // should be performed.
         if (C::ALLOW_TYPE_CHANGE || ob.cast::<PyUntypedArray>().is_err())
-            && matches!(D::NDIM, None | Some(1))
+            && matches!(D::NDIM, Some(1))
         {
             if let Ok(vec) = ob.extract::<Vec<T>>() {
                 let array = Array1::from(vec)
@@ -162,7 +163,7 @@ where
             }
         }
 
-        let (dtype, flags) = if C::ALLOW_TYPE_CHANGE {
+        let (dtype, flags) = if C::ALLOW_TYPE_CHANGE || ob.cast::<PyUntypedArray>().is_err() {
             (Some(T::get_dtype(py)), NPY_ARRAY_FORCECAST)
         } else {
             (None, 0)

tests/array_like.rs

@@ -1,5 +1,8 @@
 use ndarray::array;
-use numpy::{get_array_module, AllowTypeChange, PyArrayLike1, PyArrayLike2, PyArrayLikeDyn};
+use numpy::{
+    get_array_module, AllowTypeChange, PyArrayLike1, PyArrayLike2, PyArrayLikeDyn,
+    PyUntypedArrayMethods as _,
+};
 use pyo3::{
     ffi::c_str,
     types::{IntoPyDict, PyAnyMethods, PyDict},
@@ -115,6 +118,25 @@ fn convert_1d_list_on_extract() {
     });
 }
 
+#[test]
+fn preserve_trailing_singleton_dims() {
+    Python::attach(|py| {
+        let locals = get_np_locals(py);
+        let py_array = py
+            .eval(
+                c_str!("np.array([[1], [2], [3]], dtype='int32')"),
+                Some(&locals),
+                None,
+            )
+            .unwrap();
+        let extracted_array = py_array
+            .extract::<PyArrayLikeDyn<'_, f64, AllowTypeChange>>()
+            .unwrap();
+
+        assert_eq!(extracted_array.shape(), &[3, 1]);
+    })
+}
+
 #[test]
 fn unsafe_cast_shall_fail() {
     Python::attach(|py| {