[Python-Dev] Use of PyObject_NEW
Martin v. Loewis
martin@v.loewis.de
2002年3月15日 08:29:50 +0100
I tried to understand the various memory allocation function and
macros in Python, and found that there is probably a misunderstanding
in what PyObject_NEW does.
For example, PyRange_New says
rangeobject *obj = PyObject_NEW(rangeobject, &PyRange_Type);
if (obj == NULL)
return NULL;
The assumption apparently is that somebody will raise a MemoryError
and return NULL when allocation fails. However, this code expands to
rangeobject *obj = ((rangeobject*)PyObject_Init(
(PyObject *) malloc(((&PyRange_Type)->tp_basicsize)),
(&PyRange_Type)));
if (obj == ((void *)0) )
return ((void *)0) ;
malloc will just return NULL in case of failure, and PyObject_Init
starts with
if (op == NULL) {
PyErr_SetString(PyExc_SystemError,
"NULL object passed to PyObject_Init");
return op;
}
So instead of a MemoryError, you will get a SystemError if the system
runs out of memory. Is that intentional?
The documentation says
Macro version of \cfunction{PyObject_New()}, to gain performance at
the expense of safety. This does not check \var{type} for a \NULL{}
value.
This is incorrect: It does check for NULL. It also does not help to
gain performance - PyObject_New has three calls (_PyObject_New, malloc,
_Py_NewReference), and so does PyObject_NEW (malloc, PyObject_Init,
_Py_NewReference).
I recommend to deprecate PyObject_NEW (and correspondingly
PyObject_NEW_VAR, PyObject_DEL).
Regards,
Martin