[Python-Dev] Undocumented view==NULL argument in PyObject_GetBuffer() (original) (raw)

Stefan Krah stefan at bytereef.org
Tue Mar 6 11:34:59 CET 2012

Hello,

PyObject_GetBuffer() had an undocumented variant that was used internally:

PyObject_GetBuffer(obj, NULL, flags)

view==NULL has never been allowed by either PEP-3118 or the documentation:

PEP: "The first variable is the "exporting" object. The second argument is the address to a bufferinfo structure. Both arguments must never be NULL."

3.2 docs: "view must point to an existing Py_buffer structure allocated by the caller."

The internal use was to bump up the export count of e.g. a bytearray without bothering to have it fill in a complete Py_buffer. The increased export count would then prevent the bytearray from being resized.

However, this feature appears to be unused in the source tree. The last traces of a middle NULL argument that I found are here:

http://hg.python.org/cpython/file/df3b2b5db900/Modules/posixmodule.c#l561

So, currently the checks for NULL just slow down bytearray_getbuffer() and a couple of other getbufferprocs. Also, due to the absence of a use case it takes some VCS history digging to find out why the feature was there in the first place.

The obvious question is: Will anyone need view==NULL in the future or can we remove the special case?

Stefan Krah

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