[Numpy-discussion] Missing NULL return checks?

[Charles R Harris]

On Sat, Jul 12, 2008 at 8:42 AM, Michael Abbott <michael at araneidae.co.uk>
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 copyof 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.

Chuck
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