[Python-Dev] Py_buffer.obj documentation (original) (raw)

Stefan Krah stefan at bytereef.org
Thu Aug 30 10:53:25 CEST 2012

Alexander Belopolsky <alexander.belopolsky at gmail.com> wrote:

/* info->obj is either NULL or a borrowed reference. This reference should not be decremented in PyBufferRelease(). */

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

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