gh-155819: Add const qualifier to Py_buffer.format

Author: hpkfft

Include/pybuffer.h

@@ -25,7 +25,7 @@ typedef struct {
                              pointed to by strides in simple case.*/
     int readonly;
     int ndim;
-    char *format;
+    const char *format;
     Py_ssize_t *shape;
     Py_ssize_t *strides;
     Py_ssize_t *suboffsets;

Misc/NEWS.d/next/C_API/2026-08-14-20-39-52.gh-issue-155819.rnxJf1.rst

@@ -0,0 +1,3 @@
+The member ``format`` of ``Py_buffer`` is now of type ``const char *``
+rather than of type ``char *``.  Contributed by High Performance Kernels
+LLC.

Modules/arraymodule.c

@@ -2907,7 +2907,7 @@ array_buffer_getbuf(PyObject *op, Py_buffer *view, int flags)
     view->format = NULL;
     view->internal = NULL;
     if ((flags & PyBUF_FORMAT) == PyBUF_FORMAT) {
-        view->format = (char *)self->ob_descr->typecode;
+        view->format = self->ob_descr->typecode;
     }
 
     self->ob_exports++;

Objects/memoryobject.c

@@ -1340,7 +1340,7 @@ cast_to_1D(PyMemoryViewObject *mv, PyObject *format)
         goto out;
     }
 
-    view->format = (char *)get_native_fmtstr(PyBytes_AS_STRING(asciifmt));
+    view->format = get_native_fmtstr(PyBytes_AS_STRING(asciifmt));
     if (view->format == NULL) {
         /* NOT_REACHED: get_native_fmtchar() already validates the format. */
         PyErr_SetString(PyExc_RuntimeError,