Describe the issue:

I am finding that numpy's implementation of the bf_getbuffer function does not match the Python docs. The docs specify that certain fields are request-independent and should always be filled in, regardless of flags (see https://docs.python.org/3/c-api/buffer.html#request-independent-fields). These are obj, buf, len, itemsize, and ndim. I interpret this to mean with flags=PyBUF_SIMPLE that ndim should be set to a value. However this is not the case (as the code example shows). Reading the implementation of array_getbuffer in numpy/_core/src/multiarray/buffer.c shows that only when PyBUF_ND is apart of the flags is ndim filled in, which I believe is incorrect.

Note that the following patch is sufficient to fix the issue, if others agree I am happy to open a PR with it

diff --git a/numpy/_core/src/multiarray/buffer.c b/numpy/_core/src/multiarray/buffer.c
index fcff3ad6ca..a45399cfab 100644
--- a/numpy/_core/src/multiarray/buffer.c
+++ b/numpy/_core/src/multiarray/buffer.c
@@ -820,12 +820,11 @@ array_getbuffer(PyObject *obj, Py_buffer *view, int flags)
     } else {
         view->format = NULL;
     }
+    view->ndim = info->ndim;
     if ((flags & PyBUF_ND) == PyBUF_ND) {
-        view->ndim = info->ndim;
         view->shape = info->shape;
     }
     else {
-        view->ndim = 0;
         view->shape = NULL;
     }
     if ((flags & PyBUF_STRIDES) == PyBUF_STRIDES) {

Reproduce the code example:

#define PY_SSIZE_T_CLEAN
#include <Python.h>

// clang bug.c `python3-config --embed --cflags` `python3-config --embed --ldflags`

PyObject* newList() {
  PyObject* lst = PyList_New(5);
  if (!lst) {
    return NULL;
  }
  PyList_SetItem(lst, 0, PyLong_FromLong(1));
  PyList_SetItem(lst, 1, PyLong_FromLong(2));
  PyList_SetItem(lst, 2, PyLong_FromLong(3));
  PyList_SetItem(lst, 3, PyLong_FromLong(4));
  PyList_SetItem(lst, 4, PyLong_FromLong(5));
  return lst;
}

int main() {
  Py_Initialize();


  PyObject* numpy = PyImport_ImportModule("numpy");
  if (!numpy) {
    PyErr_Print();
    return 1;
  }

  PyObject* numpy_array = PyObject_GetAttrString(numpy, "array");
  if (!numpy_array) {
    PyErr_Print();
    return 1;
  }

  PyObject* lst = newList();
  if (!lst) {
    PyErr_Print();
    return 1;
  }
  PyObject* array = PyObject_CallOneArg(numpy_array, lst);
  if (!array) {
    PyErr_Print();
    return 1;
  }

  PyObject* ndim = PyObject_GetAttrString(array, "ndim");
  if (!ndim) {
    PyErr_Print();
    return 1;
  }
  printf("ndim from numpy: %ld\n", PyLong_AsLong(ndim));

  if (PyObject_CheckBuffer(array)) {
    Py_buffer view;
    PyObject_GetBuffer(array, &view, PyBUF_SIMPLE);
    printf("ndim from buffer: %d\n", view.ndim);
    PyBuffer_Release(&view);
  } else {
    return 1;
  }

  Py_Finalize();

  return 0;
}

Error message:

ndim from numpy: 1
ndim from buffer: 0

Python and NumPy Versions:

numpy 2.2.1
pythom 3.12.7

Runtime Environment:

[{'numpy_version': '2.2.1',
'python': '3.12.7 (main, Oct 1 2024, 02:05:46) [Clang 15.0.0 '
'(clang-1500.1.0.2.5)]',
'uname': uname_result(system='Darwin', node='<>', release='22.6.0', version='Darwin Kernel Version 22.6.0: Wed Jul 5 22:22:05 PDT 2023; root:xnu-8796.141.3~6/RELEASE_ARM64_T6000', machine='arm64')},
{'simd_extensions': {'baseline': ['NEON', 'NEON_FP16', 'NEON_VFPV4', 'ASIMD'],
'found': ['ASIMDHP'],
'not_found': ['ASIMDFHM']}},
{'architecture': 'neoversen1',
'filepath': '.venv/lib/python3.12/site-packages/numpy/.dylibs/libscipy_openblas64_.dylib',
'internal_api': 'openblas',
'num_threads': 10,
'prefix': 'libscipy_openblas',
'threading_layer': 'pthreads',
'user_api': 'blas',
'version': '0.3.28'}]

Context for the issue:

The Chapel language team is working on Python interop support, especially being able to interop closely with numpy arrays. I don't think this issue blocks that work in anyway (passing PyBUF_ND is an suitable workaround), but it would be nice to fix this and match the Python docs