[Python-Dev] Re: [Bug #121013] Bug in <stringobject>.join(<unicodestring>)
Tue, 28 Nov 2000 10:19:14 +0000 (GMT)
On Mon, 27 Nov 2000, M.-A. Lemburg wrote:
> Michael Hudson wrote:
> > > I still think that the PySequence_Fast_GETITEM() macro should at
> > > least include a fall-back type check which causes some exception in
> > > case the used object was not "fixed" using PySequence_Fast() (which
> > > I only noticed in string_join() just now).
> > It's hard to see how; you're not going to check each invocation of
> > PySequence_Fast_GETITEM for a NULL return, are you? It's possible
> > that PySequence_Fast should raise an exception on being passed a
> > string or Unicode object... but probably not.
> Since not using PySequence_Fast() to initialize the protocol,
> I'd suggest doing a Py_FatalError() with some explanatory
> text which gets printed to stderr -- still better than a
> segfault at some later point due to some dangling pointers...
So you'd want PySequence_Fast_GETITEM to look like
#define PySequence_Fast_GETITEM(s,i) \
(PyList_Check((s)) ? PyList_GET_ITEM((s),(i)) : \
(PyTuple_Check((s))? PyTuple_GET_ITEM((s),(i)) : \
? That'd probably be fair - you'd want to check any performance hit, but
I wouldn't be surprised if it was neglible.
> > > Fredrik's PySequence_Fast_* APIs look interesting, BTW. Should be
> > > used more often :-)
> > Yes. But they're pretty new, aren't they?
> Yep. Fredrik added them quite late in the 2.0 release process.
> > I find them a bit
> > unsatisfactory that it's not possible to hoist the type check out of
> > the inner loop. Still, it seems my PII's branch predictor nails that
> > one... (i.e. changing it so that it didn't check inside the loop made
> > naff-all difference to the running time).
> I think Fredrik speculated on having the compiler optimizers
> taking care of the check...
gcc 2.95.1 doesn't seem to - even with -O9 you get stuff like
... but I'm no expert in assembly reading.
> hmm, it would probably also help
> to somehow declare PyTypeObject slots "const" -- is this possible
> in a struct definition ?
I have no idea!