gh-112015: Implement ctypes.memoryview_at() (GH-112018)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Co-authored-by: Petr Viktorin <encukou@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>

Doc/library/ctypes.rst

@@ -2182,6 +2182,28 @@ Utility functions
    .. audit-event:: ctypes.wstring_at ptr,size ctypes.wstring_at
 
 
+.. function:: memoryview_at(ptr, size, readonly=False)
+
+   Return a :class:`memoryview` object of length *size* that references memory
+   starting at *void \*ptr*.
+
+   If *readonly* is true, the returned :class:`!memoryview` object can
+   not be used to modify the underlying memory.
+   (Changes made by other means will still be reflected in the returned
+   object.)
+
+   This function is similar to :func:`string_at` with the key
+   difference of not making a copy of the specified memory.
+   It is a semantically equivalent (but more efficient) alternative to
+   ``memoryview((c_byte * size).from_address(ptr))``.
+   (While :meth:`~_CData.from_address` only takes integers, *ptr* can also
+   be given as a :class:`ctypes.POINTER` or a :func:`~ctypes.byref` object.)
+
+   .. audit-event:: ctypes.memoryview_at address,size,readonly
+
+   .. versionadded:: next
+
+
 .. _ctypes-data-types:
 
 Data types

Doc/whatsnew/3.14.rst

@@ -343,6 +343,14 @@ ctypes
 * On Windows, the :func:`~ctypes.CopyComPointer` function is now public.
   (Contributed by Jun Komoda in :gh:`127275`.)
 
+* :func:`ctypes.memoryview_at` now exists to create a
+  :class:`memoryview` object that refers to the supplied pointer and
+  length. This works like :func:`ctypes.string_at` except it avoids a
+  buffer copy, and is typically useful when implementing pure Python
+  callback functions that are passed dynamically-sized buffers.
+  (Contributed by Rian Hunter in :gh:`112018`.)
+
+
 datetime
 --------