Add PyArrayDescr::new()

CHANGELOG.md

@@ -8,22 +8,23 @@
   - `PyArray::from_exact_iter` does not unsoundly trust `ExactSizeIterator::len` any more ([#262](https://github.com/PyO3/rust-numpy/pull/262))
   - `PyArray::as_cell_slice` was removed as it unsoundly interacts with `PyReadonlyArray` allowing safe code to violate aliasing rules ([#260](https://github.com/PyO3/rust-numpy/pull/260))
   - `rayon` feature is now removed, and directly specifying the feature via `ndarray` dependency is recommended ([#250](https://github.com/PyO3/rust-numpy/pull/250))
-  - Descriptors rework and related changes ([#256](https://github.com/PyO3/rust-numpy/pull/256)):
-    - Remove `DataType`
-    - Add the top-level `dtype` function for easy access to registered dtypes
-    - Add `PyArrayDescr::of`, `PyArrayDescr::into_dtype_ptr` and `PyArrayDescr::is_equiv_to`
-    - `Element` trait has been simplified to just `IS_COPY` const and `get_dtype` method
+  - `Element` trait and `PyArrayDescr` changes ([#256](https://github.com/PyO3/rust-numpy/pull/256)):
+    - `Element` trait has been simplified to `get_dtype()` and `IS_COPY`
+    - New `PyArrayDescr` methods: `of`, `into_dtype_ptr`, `is_equiv_to`
+    - Added `numpy::dtype` function
     - `Element` is now implemented for `isize`
-    - `c32` and `c64` aliases have been replaced with `Complex32` and `Complex64`
+    - `c32` / `c64` have been renamed with `Complex32` / `Complex64`
     - `ShapeError` has been split into `TypeError` and `DimensionalityError`
-    - `i32`, `i64`, `u32` and `u64` are now guaranteed to map to
-      `np.int32`, `np.int64`, `np.uint32` and `np.uint64` respectively
-    - Remove `cfg_if` dependency
-  - New methods in `PyArrayDescr`, catching up with `np.dtype`:
+    - `i32`, `i64`, `u32`, `u64` are now guaranteed to map to `np.u?int{32,64}`.
+    - Removed `cfg_if` dependency
+    - Removed `DataType` enum
+  - Added `PyArrayDescr::new` constructor
+    ([#266](https://github.com/PyO3/rust-numpy/pull/266))
+  - New `PyArrayDescr` methods
+    ([#266](https://github.com/PyO3/rust-numpy/pull/261)):
     - `num`, `base`, `ndim`, `shape`, `byteorder`, `char`, `kind`, `itemsize`,
-      `alignment`, `flags`, `has_object`, `is_aligned_struct`, `names`
-    - Added `get_field` to query fields of structured dtypes
-    - Additional helper methods: `has_subarray`, `has_fields`, `is_native_byteorder`
+      `alignment`, `flags`, `has_object`, `is_aligned_struct`, `names`,
+      `get_field`, `has_subarray`, `has_fields`, `is_native_byteorder`
     - Renamed `get_type` to `typeobj`
 
 - v0.15.1

src/dtype.rs

@@ -2,6 +2,7 @@ use std::mem::size_of;
 use std::os::raw::{
     c_char, c_int, c_long, c_longlong, c_short, c_uint, c_ulong, c_ulonglong, c_ushort,
 };
+use std::ptr;
 
 use num_traits::{Bounded, Zero};
 use pyo3::{
@@ -57,6 +58,23 @@ pub fn dtype<T: Element>(py: Python) -> &PyArrayDescr {
 }
 
 impl PyArrayDescr {
+    /// Creates a new dtype object from an arbitrary object.
+    ///
+    /// Equivalent to invoking the constructor of `np.dtype`.
+    #[inline]
+    pub fn new<'py, T: ToPyObject + ?Sized>(py: Python<'py>, obj: &T) -> PyResult<&'py Self> {
+        Self::new_impl(py, obj.to_object(py))
+    }
+
+    fn new_impl<'py>(py: Python<'py>, obj: PyObject) -> PyResult<&'py Self> {
+        let mut descr: *mut PyArray_Descr = ptr::null_mut();
+        unsafe {
+            // None is an invalid input here and is not converted to NPY_DEFAULT_TYPE
+            PY_ARRAY_API.PyArray_DescrConverter2(obj.as_ptr(), &mut descr as *mut _);
+            py.from_owned_ptr_or_err(descr as _)
+        }
+    }
+
     /// Returns `self` as `*mut PyArray_Descr`.
     pub fn as_dtype_ptr(&self) -> *mut PyArray_Descr {
         self.as_ptr() as _
@@ -423,6 +441,19 @@ mod tests {
     use super::{dtype, Complex32, Complex64, Element, PyArrayDescr};
     use crate::npyffi::{NPY_ALIGNED_STRUCT, NPY_ITEM_HASOBJECT, NPY_NEEDS_PYAPI, NPY_TYPES};
 
+    #[test]
+    fn test_dtype_new() {
+        pyo3::Python::with_gil(|py| {
+            assert_eq!(PyArrayDescr::new(py, "float64").unwrap(), dtype::<f64>(py));
+            let d = PyArrayDescr::new(py, [("a", "O"), ("b", "?")].as_ref()).unwrap();
+            assert_eq!(d.names(), Some(vec!["a", "b"]));
+            assert!(d.has_object());
+            assert_eq!(d.get_field("a").unwrap().0, dtype::<PyObject>(py));
+            assert_eq!(d.get_field("b").unwrap().0, dtype::<bool>(py));
+            assert!(PyArrayDescr::new(py, &123_usize).is_err());
+        });
+    }
+
     #[test]
     fn test_dtype_names() {
         fn type_name<T: Element>(py: pyo3::Python) -> &str {