Richard Oudkerk <report@bugs.python.org> wrote:
>     PyObject_GetBuffer(b, &buf, PyBUF_WRITABLE);
>     view = PyMemoryView_FromBuffer(&buf);
>     // readinto view
>     PyBuffer_Release(&buf);
> 
> Would attempts to access a "leaked" reference to view now result in ValueError("operation forbidden on released memoryview object")?  If so then I think this would be safe.

You would need to call memory_release(). Perhaps we can just expose it on the
C-API level as PyMemoryView_Release().

IMO the use of PyObject_GetBuffer() should be discouraged. The semantics
aren't clear (see #15821). I'd suggest using:

  1) A buffer provider is involved (the case here):

        PyMemoryView_From Object()

  2) A piece of memory needs to be wrapped temporarily and no references
     to the memoryview are "leaked" on the Python level:

        PyMemoryView_FromMemory()

  3) A piece of memory needs to be packaged as a memoryview with automatic
     cleanup in mbuf_dealloc():

        PyMemoryView_FromBufferWithCleanup() (proposed in msg169613)

So I think the combination of PyMemoryView_FromObject() with a call to
PyMemoryView_Release() should indeed work here.