[Python-Dev] Assertion in _PyManagedBuffer_FromObject()

[Stefan Behnel]

Hi,

I just stumbled over this assertion in _PyManagedBuffer_FromObject() in the
latest Py3.3 branch:

"""
static PyObject *
_PyManagedBuffer_FromObject(PyObject *base)
{
    _PyManagedBufferObject *mbuf;

    mbuf = mbuf_alloc();
    if (mbuf == NULL)
        return NULL;

    if (PyObject_GetBuffer(base, &mbuf->master, PyBUF_FULL_RO) < 0) {
        /* mbuf->master.obj must be NULL. */
        Py_DECREF(mbuf);
        return NULL;
    }

    /* Assume that master.obj is a new reference to base. */
    assert(mbuf->master.obj == base);

    return (PyObject *)mbuf;
}
"""

I'm not saying that this is likely to happen, but I could imagine code that
wants to use a different object for the cleanup than itself, possibly for
keeping a certain kind of state when it delivers more than one buffer, or
for remembering what kind of allocation was used, or ...

Given that the buffer will eventually get released by the object pointed to
by the view->obj field in the Py_buffer struct, is there a reason why it
should be asserted that this is the same as the object that originally
provided the buffer?

Stefan