[Python-Dev] ints not overflowing into longs?

Derek Shockey derek.shockey at gmail.com
Thu Nov 3 05:37:02 CET 2011

Thank you, I narrowed it down from there and got a properly working
build. I gather the problem is that in Xcode 4.2 the default compiler
was changed to clang, but the version of clang bundled with it has a
bug that breaks overflows in intobject.c.

In case anyone else hits this, I fixed this in MacPorts by forcing it
to use gcc. Edit the portfile (port edit python27) and add this
anywhere after the 5th or so line:
configure.compiler  llvm-gcc-4


On Wed, Nov 2, 2011 at 7:41 PM, Guido van Rossum <guido at python.org> wrote:
> Apparently Macports is still using a buggy compiler. I reported a
> similar issue before and got this reply from Ned Delly:
> """
> Thanks for the pointer.  That looks like a duplicate of Issue11149 (and
> Issue12701).  Another manifestation of this was reported in Issue13061
> which also originated from MacPorts.  I'll remind them that the
> configure change is likely needed for all Pythons.  It's still safest to
> stick with good old gcc-4.2 on OS X at the moment.
> """
> (Those issues are on bugs.python.org.)
> --Guido
> On Wed, Nov 2, 2011 at 7:32 PM, Derek Shockey <derek.shockey at gmail.com> wrote:
>> I just found an unexpected behavior and I'm wondering if it is a bug.
>> In my 2.7.2 interpreter on OS X, built and installed via MacPorts, it
>> appears that integers are not correctly overflowing into longs and
>> instead are yielding bizarre results. I can only reproduce this when
>> using the exponent operator with two ints (declaring either operand
>> explicitly as long prevents the behavior).
>>>>> 2**100
>> 0
>>>>> 2**100L
>> 1267650600228229401496703205376L
>>>>> 20**20
>> -2101438300051996672
>>>>> 20L**20
>> 104857600000000000000000000L
>>>>> 10**20
>> 7766279631452241920
>>>>> 10L**20L
>> 100000000000000000000L
>> To confirm I'm not crazy, I tried in the 2.7.1 and 2.6.7 installations
>> included in OS X 10.7, and also a 2.7.2+ (not sure what the + is) on
>> an Ubuntu machine and didn't see this behavior. This looks like some
>> kind of truncation error, but I don't know much about the internals of
>> Python and have no idea what's going on. I assume since it's only in
>> my MacPorts installation, it must be build configuration issue that is
>> specific to OS X, perhaps only 10.7, or MacPorts.
>> Am I doing something wrong, and is there a way to fix it before I
>> compile? I could find any references to this problem as a known issue.
>> Thanks,
>> Derek
>> _______________________________________________
>> Python-Dev mailing list
>> Python-Dev at 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 (python.org/~guido)

More information about the Python-Dev mailing list