Argh. I also find it a bug.
I also feel responsible because I reviewed the patch. :-( In my recollection I tried to avoid this exact behavior. I wanted __index__() to just return the unclipped int or long value, but have a C API that clipped it for use in slice operations. It looks like I failed (the patch went through so many revisions that at some point I must've stopped caring). --Guido On 7/28/06, Nick Coghlan <[EMAIL PROTECTED]> wrote: > David Hopwood wrote: > > Armin Rigo wrote: > >> Hi, > >> > >> There is an oversight in the design of __index__() that only just > >> surfaced :-( It is responsible for the following behavior, on a 32-bit > >> machine with >= 2GB of RAM: > >> > >> >>> s = 'x' * (2**100) # works! > >> >>> len(s) > >> 2147483647 > >> > >> This is because PySequence_Repeat(v, w) works by applying w.__index__ in > >> order to call v->sq_repeat. However, __index__ is defined to clip the > >> result to fit in a Py_ssize_t. > > > > Clipping the result sounds like it would *never* be a good idea. What was > > the rationale for that? It should throw an exception. > > A simple demonstration of the clipping behaviour that works on machines with > limited memory: > > >>> (2**100).__index__() > 2147483647 > >>> (-2**100).__index__() > -2147483648 > > PEP 357 doesn't even mention the issue, and the comment on long_index in the > code doesn't give a rationale - it just notes that the function clips the > result. > > Neither the PyNumber_AsIndex nor the __index__ documentation mention anything > about the possibility of clipping, and there's no test case to verify this > behaviour. > > I'm inclined to call it a bug, too, but I've cc'ed Travis to see if he can > shed some light on the question - the implementation of long_index explicitly > suppresses the overflow error generated by _long_as_ssize_t, so the current > behaviour appears to be deliberate. > > Cheers, > Nick. > > -- > Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia > --------------------------------------------------------------- > http://www.boredomandlaziness.org > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/guido%40python.org > -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
