Re: [Numpy-discussion] Missing NULL return checks?

12 Jul 2008

      On Sat, Jul 12, 2008 at 10:13 AM, Charles R Harris <
charlesr.harris@gmail.com> wrote:
...
On Sat, Jul 12, 2008 at 8:42 AM, Michael Abbott 
wrote:
...
...
PyArray_DescrFromType can return NULL
Yah, you noticed ;)
...
Yet it is unchecked in several places:
Pity about that.  Easy enough to fix though -- just don't lose track of
ref counts.  In fact, I've already submitted a patch to this function (but
not addressing this issue).
...
static int
PyArray_CanCastSafely(int fromtype, int totype)
{
    PyArray_Descr *from, *to;
    register int felsize, telsize;
if (fromtype == totype) return 1;
    if (fromtype == PyArray_BOOL) return 1;
    if (totype == PyArray_BOOL) return 0;
    if (totype == PyArray_OBJECT || totype == PyArray_VOID) return 1;
    if (fromtype == PyArray_OBJECT || fromtype == PyArray_VOID) return
0;
from = PyArray_DescrFromType(fromtype);
      if (from == NULL)  return 0;
...
/*
     * cancastto is a PyArray_NOTYPE terminated C-int-array of types
that
...
* the data-type can be cast to safely.
     */
    if (from->f->cancastto) {
        int *curtype;
        curtype = from->f->cancastto;
        while (*curtype != PyArray_NOTYPE) {
            if (*curtype++ == totype) return 1;
        }
    }
    if (PyTypeNum_ISUSERDEF(totype)) return 0;
to = PyArray_DescrFromType(totype);
if (to == NULL)  { Py_DECREF(from); return 0; }
...
telsize = to->elsize;
    felsize = from->elsize;
    Py_DECREF(from);
    Py_DECREF(to);
      ...
}
Furthermore, the last function can fail, but doesn't seem to have an
error
...
return. What is the best way to go about cleaning this up?
Given the question the function is asking, returning false seems good
enough for "failure".
Good point, but  a memory error may have been set by PyArray_DescrNew. My
impression is that the routine was originally intended to return references
to static singleton instances, in which case it couldn't fail.  I think we
need a separate static instance for PyArray_CHARLTR instead of making a
copy of a string type and fudging a few members so that it too can't fail.
The array indexing for user defined types probably needs bounds checking
also, but I'm not sure what to do there.
This bit looks hinky, too:

    else {
        int num = PyArray_NTYPES;
        if (type < _MAX_LETTER) {
            num = (int) _letter_to_num[type];
        }
        if (num >= PyArray_NTYPES) {
            ret = NULL;
        }
        else {
            ret = _builtin_descrs[num];
        }

Type shouldn't have alternate meanings. Maybe this is a backwards
compatibility thing.  We could write a new function that doesn't set any
Python errors, leaving that to higher level routines.

Chuck