[New-bugs-announce] [issue10538] PyArg_ParseTuple("s*") does not always incref object

Kristján Valur Jónsson report at bugs.python.org
Fri Nov 26 09:07:33 CET 2010

New submission from Kristján Valur Jónsson <kristjan at ccpgames.com>:

The new "s*" code for PyArg_ParseTuple is used to fill a Py_buffer object from the arguments.  This object must be relased using PyBuffer_Release() after use.

However, if the object in the tuple does not support the new buffer interface, the old buffer interface is queried and the Py_buffer object is manually filled in.  For this case, the source object is _not_ increfed and buffer.obj remains set to 0.

This causes different semantics in the function for objects that are passed in:  If the Py_buffer interface is supported directly, then it is safe for the function to store this and release this at a later time.  If it isn't supported, then no extra reference to the object is got and the function cannot safely keep the Py_buffer object around.

The Fix is as follows:  Change line 1402 of getargs.c from:
PyBuffer_FillInfo(view, NULL, buf, count, 1, 0);
PyBuffer_FillInfo(view, arg, buf, count, 1, 0);

messages: 122445
nosy: krisvale
priority: normal
severity: normal
status: open
title: PyArg_ParseTuple("s*") does not always incref object
type: behavior
versions: Python 2.7, Python 3.2

Python tracker <report at bugs.python.org>

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