[Python-Dev] Py_buffer.obj documentation

[Stefan Krah]

Alexander Belopolsky <alexander.belopolsky at gmail.com> wrote:
>  /* info->obj is either NULL or a borrowed reference. This
>     reference should not be decremented in PyBuffer_Release(). */

The semantics of PyMemoryView_FromBuffer() are problematic. This function
is the odd one in memoryobject.c since it's the only function that breaks
the link in consumer -> exporter chains. This has several consequences:

   1) One can't rely on the fact that 'info' has PyBUF_FULL information.
      This is a major inconvenience and the reason for *a lot* of code
      in memoryobject.c that reconstructs PyBUF_FULL information.

   2) One has to make a decision whether PyMemoryView_FromBuffer() steals
      the reference to view.obj or treats it as a borrowed reference.



My view on this is that it's safer to treat it as a borrowed reference.


Additionally, I can't see a scenario where PyMemoryView_FromBuffer(info)
could be used for creating a non-temporary memoryview with automatic
decref of info.obj: If 'info' is allocated on the stack, then the
memoryview shouldn't be returned from a function. If 'info' is allocated
on the heap, then who frees 'info' when the memoryview is deallocated?


Permanent memoryviews can now be safely created with PyMemoryView_FromMemory().
PyMemoryView_FromBuffer() isn't really that useful any more.


It's hard to document all this in a few lines. Perhaps you can open an
issue for this?



Stefan Krah