Merge pull request numpy#27434 from ngoldbaum/fix-dtype-new-dtype

ENH: make np.dtype(scalar_type) return the default dtype instance

Author: ngoldbaum

numpy/_core/src/multiarray/array_coercion.c

@@ -247,13 +247,17 @@ npy_discover_dtype_from_pytype(PyTypeObject *pytype)
 }
 
 /*
- * Note: This function never fails, but will return `NULL` for unknown scalars
- *       and `None` for known array-likes (e.g. tuple, list, ndarray).
+ * Note: This function never fails, but will return `NULL` for unknown scalars or
+ *       known array-likes (e.g. tuple, list, ndarray).
  */
 NPY_NO_EXPORT PyObject *
 PyArray_DiscoverDTypeFromScalarType(PyTypeObject *pytype)
 {
-    return (PyObject *)npy_discover_dtype_from_pytype(pytype);
+    PyObject *DType = (PyObject *)npy_discover_dtype_from_pytype(pytype);
+    if (DType == NULL || DType == Py_None) {
+        return NULL;
+    }
+    return DType;
 }
 
 

numpy/_core/src/multiarray/descriptor.c

@@ -29,6 +29,7 @@
 #include "npy_buffer.h"
 #include "dtypemeta.h"
 #include "stringdtype/dtype.h"
+#include "array_coercion.h"
 
 #ifndef PyDictProxy_Check
 #define PyDictProxy_Check(obj) (Py_TYPE(obj) == &PyDictProxy_Type)
@@ -1600,6 +1601,10 @@ _convert_from_type(PyObject *obj) {
         return PyArray_DescrFromType(NPY_OBJECT);
     }
     else {
+        PyObject *DType = PyArray_DiscoverDTypeFromScalarType(typ);
+        if (DType != NULL) {
+            return PyArray_GetDefaultDescr((PyArray_DTypeMeta *)DType);
+        }
         PyArray_Descr *ret = _try_convert_from_dtype_attr(obj);
         if ((PyObject *)ret != Py_NotImplemented) {
             return ret;

numpy/_core/src/multiarray/scalarapi.c

@@ -390,6 +390,12 @@ PyArray_DescrFromTypeObject(PyObject *type)
         Py_INCREF(type);
         return (PyArray_Descr *)new;
     }
+
+    PyObject *DType = PyArray_DiscoverDTypeFromScalarType((PyTypeObject *)type);
+    if (DType != NULL) {
+        return PyArray_GetDefaultDescr((PyArray_DTypeMeta *)DType);
+    }
+
     return _descr_from_subtype(type);
 }