On Tue, Jan 31, 2012 at 6:09 PM, Ian Kelly <ian.g.ke...@gmail.com> wrote: > On Tue, Jan 31, 2012 at 5:53 PM, Chris Angelico <ros...@gmail.com> wrote: >> On Wed, Feb 1, 2012 at 9:03 AM, Duncan Booth >> <duncan.booth@invalid.invalid> wrote: >>> Abitrarily nested tuples of exceptions cannot contain loops so the code >>> simply needs to walk through the tuples until it finds a match. >> >> Is this absolutely guaranteed? The C API for CPython provides: >> (Py2) http://docs.python.org/c-api/tuple.html#PyTuple_SetItem >> (Py3) http://docs.python.org/dev/c-api/tuple.html#PyTuple_SetItem >> >> which doesn't have massive warnings on it saying "USE THIS ONLY TO >> INITIALIZE A TUPLE" (compare, for instance, _PyTuple_Resize which does >> carry a similar warning). Is the assumption then that we're all >> adults, and that mutating a tuple is like passing a null pointer to an >> API function (aka "loaded gun in proximity to foot")? > > I don't know why the docs are written the way that they are, but if > you check the code, you can see that PyTuple_SetItem will raise a > SystemError if the reference count is anything other than 1. So I > think that it is only meant to be used with similar caution and > restraint.
Incidentally, I *think* that any correctly written C code attempting to nest a tuple inside itself would make the reference count of the tuple be at least 2 at the time of the call, and so it would fail. -- http://mail.python.org/mailman/listinfo/python-list
